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VALGRIND(1) valgrind VALGRIND(1)

NAME
valgrind - a suite of tools for debugging and profiling programs

SYNOPSIS
valgrind [valgrind-options] [your-program] [your-program-options]

DESCRIPTION
Valgrind is a flexible program for debugging and profiling Linux executa-
bles. It consists of a core, which provides a synthetic CPU in software,
and a series of debugging and profiling tools. The architecture is modular,
so that new tools can be created easily and without disturbing the existing
structure.

Some of the options described below work with all Valgrind tools, and some
only work with a few or one. The section MEMCHECK OPTIONS and those below
it describe tool-specific options.

This manual page covers only basic usage and options. For more comprehen-
sive information, please see the HTML documentation on your system: $IN-
STALL/share/doc/valgrind/html/index.html, or online: http://www.val-
grind.org/docs/manual/index.html.

TOOL SELECTION OPTIONS
The single most important option.

--tool=<toolname> [default: memcheck]
Run the Valgrind tool called toolname, e.g. memcheck, cachegrind, call-
grind, helgrind, drd, massif, dhat, lackey, none, exp-bbv, etc.

BASIC OPTIONS
These options work with all tools.

-h --help
Show help for all options, both for the core and for the selected tool.
If the option is repeated it is equivalent to giving --help-debug.

--help-debug
Same as --help, but also lists debugging options which usually are only
of use to Valgrind's developers.

--version
Show the version number of the Valgrind core. Tools can have their own
version numbers. There is a scheme in place to ensure that tools only
execute when the core version is one they are known to work with. This
was done to minimise the chances of strange problems arising from
tool-vs-core version incompatibilities.

-q, --quiet
Run silently, and only print error messages. Useful if you are running
regression tests or have some other automated test machinery.

-v, --verbose
Be more verbose. Gives extra information on various aspects of your
program, such as: the shared objects loaded, the suppressions used, the
progress of the instrumentation and execution engines, and warnings
about unusual behaviour. Repeating the option increases the verbosity
level.

--trace-children=<yes|no> [default: no]
When enabled, Valgrind will trace into sub-processes initiated via the
exec system call. This is necessary for multi-process programs.

Note that Valgrind does trace into the child of a fork (it would be
difficult not to, since fork makes an identical copy of a process), so
this option is arguably badly named. However, most children of fork
calls immediately call exec anyway.

--trace-children-skip=patt1,patt2,...
This option only has an effect when --trace-children=yes is specified.
It allows for some children to be skipped. The option takes a comma
separated list of patterns for the names of child executables that Val-
grind should not trace into. Patterns may include the metacharacters ?
and *, which have the usual meaning.

This can be useful for pruning uninteresting branches from a tree of
processes being run on Valgrind. But you should be careful when using
it. When Valgrind skips tracing into an executable, it doesn't just
skip tracing that executable, it also skips tracing any of that exe-
cutable's child processes. In other words, the flag doesn't merely
cause tracing to stop at the specified executables -- it skips tracing
of entire process subtrees rooted at any of the specified executables.

--trace-children-skip-by-arg=patt1,patt2,...
This is the same as --trace-children-skip, with one difference: the de-
cision as to whether to trace into a child process is made by examining
the arguments to the child process, rather than the name of its exe-
cutable.

--child-silent-after-fork=<yes|no> [default: no]
When enabled, Valgrind will not show any debugging or logging output
for the child process resulting from a fork call. This can make the
output less confusing (although more misleading) when dealing with
processes that create children. It is particularly useful in conjunc-
tion with --trace-children=. Use of this option is also strongly recom-
mended if you are requesting XML output (--xml=yes), since otherwise
the XML from child and parent may become mixed up, which usually makes
it useless.

--vgdb=<no|yes|full> [default: yes]
Valgrind will provide "gdbserver" functionality when --vgdb=yes or
--vgdb=full is specified. This allows an external GNU GDB debugger to
control and debug your program when it runs on Valgrind. --vgdb=full
incurs significant performance overheads, but provides more precise
breakpoints and watchpoints. See Debugging your program using Val-
grind's gdbserver and GDB for a detailed description.

If the embedded gdbserver is enabled but no gdb is currently being
used, the vgdb command line utility can send "monitor commands" to Val-
grind from a shell. The Valgrind core provides a set of Valgrind moni-
tor commands. A tool can optionally provide tool specific monitor com-
mands, which are documented in the tool specific chapter.

--vgdb-error=<number> [default: 999999999]
Use this option when the Valgrind gdbserver is enabled with --vgdb=yes
or --vgdb=full. Tools that report errors will wait for "number" errors
to be reported before freezing the program and waiting for you to con-
nect with GDB. It follows that a value of zero will cause the gdbserver
to be started before your program is executed. This is typically used
to insert GDB breakpoints before execution, and also works with tools
that do not report errors, such as Massif.

--vgdb-stop-at=<set> [default: none]
Use this option when the Valgrind gdbserver is enabled with --vgdb=yes
or --vgdb=full. The Valgrind gdbserver will be invoked for each error
after --vgdb-error have been reported. You can additionally ask the
Valgrind gdbserver to be invoked for other events, specified in one of
the following ways:

* a comma separated list of one or more of startup exit abexit val-
grindabexit.

The values startup exit valgrindabexit respectively indicate to in-
voke gdbserver before your program is executed, after the last in-
struction of your program, on Valgrind abnormal exit (e.g. internal
error, out of memory, ...).

The option abexit is similar to exit but tells to invoke gdbserver
only when your application exits abnormally (i.e. with an exit code
different of 0).

Note: startup and --vgdb-error=0 will both cause Valgrind gdbserver
to be invoked before your program is executed. The --vgdb-error=0
will in addition cause your program to stop on all subsequent er-
rors.

* all to specify the complete set. It is equivalent to
--vgdb-stop-at=startup,exit,abexit,valgrindabexit.

* none for the empty set.

--track-fds=<yes|no|all|bad> [default: no]
When enabled, Valgrind will track all file descriptor usage. It will
produce errors for bad file descriptor usage like closing a file de-
scriptor twice, using a file descriptor (number) that was never cre-
ated, or passing an already closed file descriptor to a system call. It
will also print out a list of open file descriptors on exit. Or on re-
quest, via the gdbserver monitor command v.info open_fds.

When an error is generated, or when listing the still open file de-
scriptors at exit, a stack backtrace of where the file was opened is
printed. If the file descriptor has already been closed, it will also
include a backtrace of where it was previously closed. Any error will
include details relating to the file descriptor such as the file name
or socket details.

Use all to also include reporting on stdin, stdout and stderr (or other
inherited file descriptors) at exit. If bad option is used, then ex-
clude reporting on leaked file descriptors at exit and only produce er-
rors about bad file decriptors usage.

--modify-fds=<no|yes|high> [default: no]
When enabled, when the program opens a new file descriptor, the highest
available file descriptor is returned instead of the lowest one. Use
yes to restrict the feature from the 0/1/2 file descriptors as they're
often used for stdout/stderr redirection.

--time-stamp=<yes|no> [default: no]
When enabled, each message is preceded with an indication of the
elapsed wallclock time since startup, expressed as days, hours, min-
utes, seconds and milliseconds.

--log-fd=<number> [default: 2, stderr]
Specifies that Valgrind should send all of its messages to the speci-
fied file descriptor. The default, 2, is the standard error channel
(stderr). Note that this may interfere with the client's own use of
stderr, as Valgrind's output will be interleaved with any output that
the client sends to stderr.

--log-file=<filename>
Specifies that Valgrind should send all of its messages to the speci-
fied file. If the file name is empty, it causes an abort. There are
three special format specifiers that can be used in the file name.

%p is replaced with the current process ID. This is very useful for
program that invoke multiple processes. WARNING: If you use
--trace-children=yes and your program invokes multiple processes OR
your program forks without calling exec afterwards, and you don't use
this specifier (or the %q specifier below), the Valgrind output from
all those processes will go into one file, possibly jumbled up, and
possibly incomplete. Note: If the program forks and calls exec after-
wards, Valgrind output of the child from the period between fork and
exec will be lost. Fortunately this gap is really tiny for most pro-
grams; and modern programs use posix_spawn anyway.

%n is replaced with a file sequence number unique for this process.
This is useful for processes that produces several files from the same
filename template.

%q{FOO} is replaced with the contents of the environment variable FOO.
If the {FOO} part is malformed, it causes an abort. This specifier is
rarely needed, but very useful in certain circumstances (eg. when run-
ning MPI programs). The idea is that you specify a variable which will
be set differently for each process in the job, for example BPROC_RANK
or whatever is applicable in your MPI setup. If the named environment
variable is not set, it causes an abort. Note that in some shells, the
{ and } characters may need to be escaped with a backslash.

%% is replaced with %.

If an % is followed by any other character, it causes an abort.

If the file name specifies a relative file name, it is put in the pro-
gram's initial working directory: this is the current directory when
the program started its execution after the fork or after the exec. If
it specifies an absolute file name (ie. starts with '/') then it is put
there.

--log-socket=<ip-address:port-number>
Specifies that Valgrind should send all of its messages to the speci-
fied port at the specified IP address. The port may be omitted, in
which case port 1500 is used. If a connection cannot be made to the
specified socket, Valgrind falls back to writing output to the standard
error (stderr). This option is intended to be used in conjunction with
the valgrind-listener program. For further details, see the commentary
in the manual.

--enable-debuginfod=<no|yes> [default: yes]
When enabled Valgrind will attempt to download missing debuginfo from
debuginfod servers if space-separated server URLs are present in the
$DEBUGINFOD_URLS environment variable. This option is supported on
Linux only.

ERROR-RELATED OPTIONS
These options are used by all tools that can report errors, e.g. Memcheck,
but not Cachegrind.

--xml=<yes|no> [default: no]
When enabled, the important parts of the output (e.g. tool error mes-
sages) will be in XML format rather than plain text. Furthermore, the
XML output will be sent to a different output channel than the plain
text output. Therefore, you also must use one of --xml-fd, --xml-file
or --xml-socket to specify where the XML is to be sent.

Less important messages will still be printed in plain text, but be-
cause the XML output and plain text output are sent to different output
channels (the destination of the plain text output is still controlled
by --log-fd, --log-file and --log-socket) this should not cause prob-
lems.

This option is aimed at making life easier for tools that consume Val-
grind's output as input, such as GUI front ends. Currently this option
works with Memcheck, Helgrind and DRD. The output format is specified
in the file docs/internals/xml-output-protocol4.txt in the source tree
for Valgrind 3.5.0 or later.

The recommended options for a GUI to pass, when requesting XML output,
are: --xml=yes to enable XML output, --xml-file to send the XML output
to a (presumably GUI-selected) file, --log-file to send the plain text
output to a second GUI-selected file, --child-silent-after-fork=yes,
and -q to restrict the plain text output to critical error messages
created by Valgrind itself. For example, failure to read a specified
suppressions file counts as a critical error message. In this way, for
a successful run the text output file will be empty. But if it isn't
empty, then it will contain important information which the GUI user
should be made aware of.

--xml-fd=<number> [default: -1, disabled]
Specifies that Valgrind should send its XML output to the specified
file descriptor. It must be used in conjunction with --xml=yes.

--xml-file=<filename>
Specifies that Valgrind should send its XML output to the specified
file. It must be used in conjunction with --xml=yes. Any %p or %q se-
quences appearing in the filename are expanded in exactly the same way
as they are for --log-file. See the description of --log-file for de-
tails.

--xml-socket=<ip-address:port-number>
Specifies that Valgrind should send its XML output the specified port
at the specified IP address. It must be used in conjunction with
--xml=yes. The form of the argument is the same as that used by
--log-socket. See the description of --log-socket for further details.

--xml-user-comment=<string>
Embeds an extra user comment string at the start of the XML output.
Only works when --xml=yes is specified; ignored otherwise.

--demangle=<yes|no> [default: yes]
Enable/disable automatic demangling (decoding) of C++, D, Rust, Java,
Ada names. Enabled by default. When enabled, Valgrind will attempt to
translate encoded names in the listed languages back to something ap-
proaching the original. Note that the callgrind tool always disables
Ada demangling in order to differentiate overloaded functions and pro-
cedures in the callgraph. The demangler handles symbols mangled by g++
versions 2.X, 3.X and 4.X.

An important fact about demangling is that function names mentioned in
suppressions files should be in their mangled form. Valgrind does not
demangle function names when searching for applicable suppressions, be-
cause to do otherwise would make suppression file contents dependent on
the state of Valgrind's demangling machinery, and also slow down sup-
pression matching.

--num-callers=<number> [default: 12]
Specifies the maximum number of entries shown in stack traces that
identify program locations. Note that errors are commoned up using only
the top four function locations (the place in the current function, and
that of its three immediate callers). So this doesn't affect the total
number of errors reported.

The maximum value for this is 500. Note that higher settings will make
Valgrind run a bit more slowly and take a bit more memory, but can be
useful when working with programs with deeply-nested call chains.

--unw-stack-scan-thresh=<number> [default: 0] ,
--unw-stack-scan-frames=<number> [default: 5]
Stack-scanning support is available only on ARM targets.

These flags enable and control stack unwinding by stack scanning. When
the normal stack unwinding mechanisms -- usage of Dwarf CFI records,
and frame-pointer following -- fail, stack scanning may be able to re-
cover a stack trace.

Note that stack scanning is an imprecise, heuristic mechanism that may
give very misleading results, or none at all. It should be used only in
emergencies, when normal unwinding fails, and it is important to never-
theless have stack traces.

Stack scanning is a simple technique: the unwinder reads words from the
stack, and tries to guess which of them might be return addresses, by
checking to see if they point just after ARM or Thumb call instruc-
tions. If so, the word is added to the backtrace.

The main danger occurs when a function call returns, leaving its return
address exposed, and a new function is called, but the new function
does not overwrite the old address. The result of this is that the
backtrace may contain entries for functions which have already re-
turned, and so be very confusing.

A second limitation of this implementation is that it will scan only
the page (4KB, normally) containing the starting stack pointer. If the
stack frames are large, this may result in only a few (or not even any)
being present in the trace. Also, if you are unlucky and have an ini-
tial stack pointer near the end of its containing page, the scan may
miss all interesting frames.

By default stack scanning is disabled. The normal use case is to ask
for it when a stack trace would otherwise be very short. So, to enable
it, use --unw-stack-scan-thresh=number. This requests Valgrind to try
using stack scanning to "extend" stack traces which contain fewer than
number frames.

If stack scanning does take place, it will only generate at most the
number of frames specified by --unw-stack-scan-frames. Typically, stack
scanning generates so many garbage entries that this value is set to a
low value (5) by default. In no case will a stack trace larger than the
value specified by --num-callers be created.

--error-limit=<yes|no> [default: yes]
When enabled, Valgrind stops reporting errors after 10,000,000 in to-
tal, or 1,000 different ones, have been seen. This is to stop the error
tracking machinery from becoming a huge performance overhead in pro-
grams with many errors.

--error-exitcode=<number> [default: 0]
Specifies an alternative exit code to return if Valgrind reported any
errors in the run. When set to the default value (zero), the return
value from Valgrind will always be the return value of the process be-
ing simulated. When set to a nonzero value, that value is returned in-
stead, if Valgrind detects any errors. This is useful for using Val-
grind as part of an automated test suite, since it makes it easy to de-
tect test cases for which Valgrind has reported errors, just by in-
specting return codes. When set to a nonzero value and Valgrind detects
no error, the return value of Valgrind will be the return value of the
program being simulated.

--exit-on-first-error=<yes|no> [default: no]
If this option is enabled, Valgrind exits on the first error. A nonzero
exit value must be defined using --error-exitcode option. Useful if you
are running regression tests or have some other automated test machin-
ery.

--error-markers=<begin>,<end> [default: none]
When errors are output as plain text (i.e. XML not used), --error-mark-
ers instructs to output a line containing the begin (end) string before
(after) each error.

Such marker lines facilitate searching for errors and/or extracting er-
rors in an output file that contain valgrind errors mixed with the pro-
gram output.

Note that empty markers are accepted. So, only using a begin (or an
end) marker is possible.

--show-error-list=no|yes|all [default: no]
If this option is yes, for tools that report errors, valgrind will show
the list of detected errors and the list of used suppressions at exit.
The value all indicates to also show the list of suppressed errors.

Note that at verbosity 2 and above, valgrind automatically shows the
list of detected errors and the list of used suppressions at exit, un-
less --show-error-list=no is selected.

-s
Specifying -s is equivalent to --show-error-list=yes.

--sigill-diagnostics=<yes|no> [default: yes]
Enable/disable printing of illegal instruction diagnostics. Enabled by
default, but defaults to disabled when --quiet is given. The default
can always be explicitly overridden by giving this option.

When enabled, a warning message will be printed, along with some diag-
nostics, whenever an instruction is encountered that Valgrind cannot
decode or translate, before the program is given a SIGILL signal. Often
an illegal instruction indicates a bug in the program or missing sup-
port for the particular instruction in Valgrind. But some programs do
deliberately try to execute an instruction that might be missing and
trap the SIGILL signal to detect processor features. Using this flag
makes it possible to avoid the diagnostic output that you would other-
wise get in such cases.

--keep-debuginfo=<yes|no> [default: no]
When enabled, keep ("archive") symbols and all other debuginfo for un-
loaded code. This allows saved stack traces to include file/line info
for code that has been dlclose'd (or similar). Be careful with this,
since it can lead to unbounded memory use for programs which repeatedly
load and unload shared objects.

Some tools and some functionalities have only limited support for
archived debug info. Memcheck fully supports it. Generally, tools that
report errors can use archived debug info to show the error stack
traces. The known limitations are: Helgrind's past access stack trace
of a race condition is does not use archived debug info. Massif (and
more generally the xtree Massif output format) does not make use of
archived debug info. Only Memcheck has been (somewhat) tested with
--keep-debuginfo=yes, so other tools may have unknown limitations.

--show-below-main=<yes|no> [default: no]
By default, stack traces for errors do not show any functions that ap-
pear beneath main because most of the time it's uninteresting C library
stuff and/or gobbledygook. Alternatively, if main is not present in the
stack trace, stack traces will not show any functions below main-like
functions such as glibc's __libc_start_main. Furthermore, if main-like
functions are present in the trace, they are normalised as (below
main), in order to make the output more deterministic.

If this option is enabled, all stack trace entries will be shown and
main-like functions will not be normalised.

--fullpath-after=<string> [default: don't show source paths]
By default Valgrind only shows the filenames in stack traces, but not
full paths to source files. When using Valgrind in large projects where
the sources reside in multiple different directories, this can be in-
convenient. --fullpath-after provides a flexible solution to this
problem. When this option is present, the path to each source file is
shown, with the following all-important caveat: if string is found in
the path, then the path up to and including string is omitted, else the
path is shown unmodified. Note that string is not required to be a pre-
fix of the path.

For example, consider a file named /home/jane-
doe/blah/src/foo/bar/xyzzy.c. Specifying --fullpath-after=/home/jane-
doe/blah/src/ will cause Valgrind to show the name as foo/bar/xyzzy.c.

Because the string is not required to be a prefix, --fullpath-af-
ter=src/ will produce the same output. This is useful when the path
contains arbitrary machine-generated characters. For example, the path
/my/build/dir/C32A1B47/blah/src/foo/xyzzy can be pruned to foo/xyzzy
using --fullpath-after=/blah/src/.

If you simply want to see the full path, just specify an empty string:
--fullpath-after=. This isn't a special case, merely a logical conse-
quence of the above rules.

Finally, you can use --fullpath-after multiple times. Any appearance of
it causes Valgrind to switch to producing full paths and applying the
above filtering rule. Each produced path is compared against all the
--fullpath-after-specified strings, in the order specified. The first
string to match causes the path to be truncated as described above. If
none match, the full path is shown. This facilitates chopping off pre-
fixes when the sources are drawn from a number of unrelated directo-
ries.

--extra-debuginfo-path=<path> [default: undefined and unused]
By default Valgrind searches in several well-known paths for debug ob-
jects, such as /usr/lib/debug/.

However, there may be scenarios where you may wish to put debug objects
at an arbitrary location, such as external storage when running Val-
grind on a mobile device with limited local storage. Another example
might be a situation where you do not have permission to install debug
object packages on the system where you are running Valgrind.

In these scenarios, you may provide an absolute path as an extra, final
place for Valgrind to search for debug objects by specifying --ex-
tra-debuginfo-path=/path/to/debug/objects. The given path will be
prepended to the absolute path name of the searched-for object. For ex-
ample, if Valgrind is looking for the debuginfo for /w/x/y/zz.so and
--extra-debuginfo-path=/a/b/c is specified, it will look for a debug
object at /a/b/c/w/x/y/zz.so.

This flag should only be specified once. If it is specified multiple
times, only the last instance is honoured.

--debuginfo-server=ipaddr:port [default: undefined and unused]
This is a new, experimental, feature introduced in version 3.9.0.

In some scenarios it may be convenient to read debuginfo from objects
stored on a different machine. With this flag, Valgrind will query a
debuginfo server running on ipaddr and listening on port port, if it
cannot find the debuginfo object in the local filesystem.

The debuginfo server must accept TCP connections on port port. The de-
buginfo server is contained in the source file auxprogs/val-
grind-di-server.c. It will only serve from the directory it is started
in. port defaults to 1500 in both client and server if not specified.

If Valgrind looks for the debuginfo for /w/x/y/zz.so by using the de-
buginfo server, it will strip the pathname components and merely re-
quest zz.so on the server. That in turn will look only in its current
working directory for a matching debuginfo object.

The debuginfo data is transmitted in small fragments (8 KB) as re-
quested by Valgrind. Each block is compressed using LZO to reduce
transmission time. The implementation has been tuned for best perfor-
mance over a single-stage 802.11g (WiFi) network link.

Note that checks for matching primary vs debug objects, using GNU de-
buglink CRC scheme, are performed even when using the debuginfo server.
To disable such checking, you need to also specify --allow-mis-
matched-debuginfo=yes.

By default the Valgrind build system will build valgrind-di-server for
the target platform, which is almost certainly not what you want. So
far we have been unable to find out how to get automake/autoconf to
build it for the build platform. If you want to use it, you will have
to recompile it by hand using the command shown at the top of aux-
progs/valgrind-di-server.c.

Valgrind can also download debuginfo via debuginfod. See the DEBUGINFOD
section for more information.

--allow-mismatched-debuginfo=no|yes [no]
When reading debuginfo from separate debuginfo objects, Valgrind will
by default check that the main and debuginfo objects match, using the
GNU debuglink mechanism. This guarantees that it does not read debug-
info from out of date debuginfo objects, and also ensures that Valgrind
can't crash as a result of mismatches.

This check can be overridden using --allow-mismatched-debuginfo=yes.
This may be useful when the debuginfo and main objects have not been
split in the proper way. Be careful when using this, though: it dis-
ables all consistency checking, and Valgrind has been observed to crash
when the main and debuginfo objects don't match.

--suppressions=<filename> [default: $PREFIX/lib/valgrind/default.supp]
Specifies an extra file from which to read descriptions of errors to
suppress. You may use up to 100 extra suppression files.

--gen-suppressions=<yes|no|all> [default: no]
When set to yes, Valgrind will pause after every error shown and print
the line:

---- Print suppression ? --- [Return/N/n/Y/y/C/c] ----

Pressing Ret, or N Ret or n Ret, causes Valgrind continue execution
without printing a suppression for this error.

Pressing Y Ret or y Ret causes Valgrind to write a suppression for this
error. You can then cut and paste it into a suppression file if you
don't want to hear about the error in the future.

When set to all, Valgrind will print a suppression for every reported
error, without querying the user.

This option is particularly useful with C++ programs, as it prints out
the suppressions with mangled names, as required.

Note that the suppressions printed are as specific as possible. You may
want to common up similar ones, by adding wildcards to function names,
and by using frame-level wildcards. The wildcarding facilities are pow-
erful yet flexible, and with a bit of careful editing, you may be able
to suppress a whole family of related errors with only a few suppres-
sions.

Sometimes two different errors are suppressed by the same suppression,
in which case Valgrind will output the suppression more than once, but
you only need to have one copy in your suppression file (but having
more than one won't cause problems). Also, the suppression name is
given as <insert a suppression name here>; the name doesn't really mat-
ter, it's only used with the -v option which prints out all used sup-
pression records.

--input-fd=<number> [default: 0, stdin]
When using --gen-suppressions=yes, Valgrind will stop so as to read
keyboard input from you when each error occurs. By default it reads
from the standard input (stdin), which is problematic for programs
which close stdin. This option allows you to specify an alternative
file descriptor from which to read input.

--dsymutil=no|yes [yes]
This option is only relevant when running Valgrind on macOS.

macOS uses a deferred debug information (debuginfo) linking scheme.
When object files containing debuginfo are linked into a .dylib or an
executable, the debuginfo is not copied into the final file. Instead,
the debuginfo must be linked manually by running dsymutil, a sys-
tem-provided utility, on the executable or .dylib. The resulting com-
bined debuginfo is placed in a directory alongside the executable or
.dylib, but with the extension .dSYM.

With --dsymutil=no, Valgrind will detect cases where the .dSYM direc-
tory is either missing, or is present but does not appear to match the
associated executable or .dylib, most likely because it is out of date.
In these cases, Valgrind will print a warning message but take no fur-
ther action.

With --dsymutil=yes, Valgrind will, in such cases, automatically run
dsymutil as necessary to bring the debuginfo up to date. For all prac-
tical purposes, if you always use --dsymutil=yes, then there is never
any need to run dsymutil manually or as part of your applications's
build system, since Valgrind will run it as necessary.

Valgrind will not attempt to run dsymutil on any executable or library
in /usr/, /bin/, /sbin/, /opt/, /sw/, /System/, /Library/ or /Applica-
tions/ since dsymutil will always fail in such situations. It fails
both because the debuginfo for such pre-installed system components is
not available anywhere, and also because it would require write privi-
leges in those directories.

Be careful when using --dsymutil=yes, since it will cause pre-existing
.dSYM directories to be silently deleted and re-created. Also note that
dsymutil is quite slow, sometimes excessively so.

--max-stackframe=<number> [default: 2000000]
The maximum size of a stack frame. If the stack pointer moves by more
than this amount then Valgrind will assume that the program is switch-
ing to a different stack.

You may need to use this option if your program has large stack-allo-
cated arrays. Valgrind keeps track of your program's stack pointer. If
it changes by more than the threshold amount, Valgrind assumes your
program is switching to a different stack, and Memcheck behaves differ-
ently than it would for a stack pointer change smaller than the thresh-
old. Usually this heuristic works well. However, if your program allo-
cates large structures on the stack, this heuristic will be fooled, and
Memcheck will subsequently report large numbers of invalid stack ac-
cesses. This option allows you to change the threshold to a different
value.

You should only consider use of this option if Valgrind's debug output
directs you to do so. In that case it will tell you the new threshold
you should specify.

In general, allocating large structures on the stack is a bad idea, be-
cause you can easily run out of stack space, especially on systems with
limited memory or which expect to support large numbers of threads each
with a small stack, and also because the error checking performed by
Memcheck is more effective for heap-allocated data than for stack-allo-
cated data. If you have to use this option, you may wish to consider
rewriting your code to allocate on the heap rather than on the stack.

--main-stacksize=<number> [default: use current 'ulimit' value]
Specifies the size of the main thread's stack.

To simplify its memory management, Valgrind reserves all required space
for the main thread's stack at startup. That means it needs to know the
required stack size at startup.

By default, Valgrind uses the current "ulimit" value for the stack
size, or 16 MB, whichever is lower. In many cases this gives a stack
size in the range 8 to 16 MB, which almost never overflows for most ap-
plications.

If you need a larger total stack size, use --main-stacksize to specify
it. Only set it as high as you need, since reserving far more space
than you need (that is, hundreds of megabytes more than you need) con-
strains Valgrind's memory allocators and may reduce the total amount of
memory that Valgrind can use. This is only really of significance on
32-bit machines.

On Linux, you may request a stack of size up to 2GB. Valgrind will stop
with a diagnostic message if the stack cannot be allocated.

--main-stacksize only affects the stack size for the program's initial
thread. It has no bearing on the size of thread stacks, as Valgrind
does not allocate those.

You may need to use both --main-stacksize and --max-stackframe to-
gether. It is important to understand that --main-stacksize sets the
maximum total stack size, whilst --max-stackframe specifies the largest
size of any one stack frame. You will have to work out the
--main-stacksize value for yourself (usually, if your applications seg-
faults). But Valgrind will tell you the needed --max-stackframe size,
if necessary.

As discussed further in the description of --max-stackframe, a require-
ment for a large stack is a sign of potential portability problems. You
are best advised to place all large data in heap-allocated memory.

--max-threads=<number> [default: 500]
By default, Valgrind can handle to up to 500 threads. Occasionally,
that number is too small. Use this option to provide a different limit.
E.g. --max-threads=3000.

--realloc-zero-bytes-frees=yes|no [default: yes for glibc no otherwise]
The behaviour of realloc() with a size of zero is implementation de-
fined in C17 and undefined in C23. Valgrind tries to work in the same
way as the underlying system and C runtime library that it was config-
ured and built on. However, if you use a different C runtime library
then this default may be wrong. If the value is yes then realloc will
deallocate the memory and return NULL. If the value is no then realloc
will not deallocate the memory and the size will be handled as though
it were one byte.

As an example, if you use Valgrind installed via a package on a Linux
distro using GNU libc but link your test executable with musl libc or
the JEMalloc library then consider using --realloc-zero-bytes-frees=no.

Address Sanitizer has a similar and even wordier option alloca-
tor_frees_and_returns_null_on_realloc_zero.

MALLOC()-RELATED OPTIONS
For tools that use their own version of malloc (e.g. Memcheck, Massif, Hel-
grind, DRD), the following options apply.

--alignment=<number> [default: 8 or 16, depending on the platform]
By default Valgrind's malloc, realloc, etc, return a block whose start-
ing address is 8-byte aligned or 16-byte aligned (the value depends on
the platform and matches the platform default). This option allows you
to specify a different alignment. The supplied value must be greater
than or equal to the default, less than or equal to 4096, and must be a
power of two.

--redzone-size=<number> [default: depends on the tool]
Valgrind's malloc, realloc, etc, add padding blocks before and after
each heap block allocated by the program being run. Such padding blocks
are called redzones. The default value for the redzone size depends on
the tool. For example, Memcheck adds and protects a minimum of 16 bytes
before and after each block allocated by the client. This allows it to
detect block underruns or overruns of up to 16 bytes.

Increasing the redzone size makes it possible to detect overruns of
larger distances, but increases the amount of memory used by Valgrind.
Decreasing the redzone size will reduce the memory needed by Valgrind
but also reduces the chances of detecting over/underruns, so is not
recommended.

--xtree-memory=none|allocs|full [none]
Tools replacing Valgrind's malloc, realloc, etc, can optionally produce
an execution tree detailing which piece of code is responsible for heap
memory usage. See Execution Trees for a detailed explanation about exe-
cution trees.

When set to none, no memory execution tree is produced.

When set to allocs, the memory execution tree gives the current number
of allocated bytes and the current number of allocated blocks.

When set to full, the memory execution tree gives 6 different measure-
ments : the current number of allocated bytes and blocks (same values
as for allocs), the total number of allocated bytes and blocks, the to-
tal number of freed bytes and blocks.

Note that the overhead in cpu and memory to produce an xtree depends on
the tool. The overhead in cpu is small for the value allocs, as the in-
formation needed to produce this report is maintained in any case by
the tool. For massif and helgrind, specifying full implies to capture a
stack trace for each free operation, while normally these tools only
capture an allocation stack trace. For Memcheck, the cpu overhead for
the value full is small, as this can only be used in combination with
--keep-stacktraces=alloc-and-free or --keep-stacktraces=al-
loc-then-free, which already records a stack trace for each free opera-
tion. The memory overhead varies between 5 and 10 words per unique
stacktrace in the xtree, plus the memory needed to record the stack
trace for the free operations, if needed specifically for the xtree.

--xtree-memory-file=<filename> [default: xtmemory.kcg.%p]
Specifies that Valgrind should produce the xtree memory report in the
specified file. Any %p or %q sequences appearing in the filename are
expanded in exactly the same way as they are for --log-file. See the
description of --log-file for details.

If the filename contains the extension .ms, then the produced file for-
mat will be a massif output file format. If the filename contains the
extension .kcg or no extension is provided or recognised, then the pro-
duced file format will be a callgrind output format.

See Execution Trees for a detailed explanation about execution trees
formats.

UNCOMMON OPTIONS
These options apply to all tools, as they affect certain obscure workings
of the Valgrind core. Most people won't need to use them.

--smc-check=<none|stack|all|all-non-file> [default: all-non-file for
x86/amd64/s390x, stack for other archs]
This option controls Valgrind's detection of self-modifying code. If no
checking is done, when a program executes some code, then overwrites it
with new code, and executes the new code, Valgrind will continue to ex-
ecute the translations it made for the old code. This will likely lead
to incorrect behaviour and/or crashes.

For "modern" architectures -- anything that's not x86, amd64 or s390x
-- the default is stack. This is because a correct program must take
explicit action to reestablish D-I cache coherence following code modi-
fication. Valgrind observes and honours such actions, with the result
that self-modifying code is transparently handled with zero extra cost.

For x86, amd64 and s390x, the program is not required to notify the
hardware of required D-I coherence syncing. Hence the default is
all-non-file, which covers the normal case of generating code into an
anonymous (non-file-backed) mmap'd area.

The meanings of the four available settings are as follows. No detec-
tion (none), detect self-modifying code on the stack (which is used by
GCC to implement nested functions) (stack), detect self-modifying code
everywhere (all), and detect self-modifying code everywhere except in
file-backed mappings (all-non-file).

Running with all will slow Valgrind down noticeably. Running with none
will rarely speed things up, since very little code gets dynamically
generated in most programs. The VALGRIND_DISCARD_TRANSLATIONS client
request is an alternative to --smc-check=all and
--smc-check=all-non-file that requires more programmer effort but al-
lows Valgrind to run your program faster, by telling it precisely when
translations need to be re-made.

--smc-check=all-non-file provides a cheaper but more limited version of
--smc-check=all. It adds checks to any translations that do not origi-
nate from file-backed memory mappings. Typical applications that gener-
ate code, for example JITs in web browsers, generate code into anony-
mous mmaped areas, whereas the "fixed" code of the browser always lives
in file-backed mappings. --smc-check=all-non-file takes advantage of
this observation, limiting the overhead of checking to code which is
likely to be JIT generated.

--read-inline-info=<yes|no> [default: see below]
When enabled, Valgrind will read information about inlined function
calls from DWARF3 debug info. This slows Valgrind startup and makes it
use more memory (typically for each inlined piece of code, 6 words and
space for the function name), but it results in more descriptive stack-
traces. Currently, this functionality is enabled by default only for
Linux, FreeBSD, Android and Solaris targets and only for the tools Mem-
check, Massif, Helgrind and DRD. Here is an example of some stacktraces
with --read-inline-info=no:

==15380== Conditional jump or move depends on uninitialised value(s)
==15380== at 0x80484EA: main (inlinfo.c:6)
==15380==
==15380== Conditional jump or move depends on uninitialised value(s)
==15380== at 0x8048550: fun_noninline (inlinfo.c:6)
==15380== by 0x804850E: main (inlinfo.c:34)
==15380==
==15380== Conditional jump or move depends on uninitialised value(s)
==15380== at 0x8048520: main (inlinfo.c:6)

And here are the same errors with --read-inline-info=yes:

==15377== Conditional jump or move depends on uninitialised value(s)
==15377== at 0x80484EA: fun_d (inlinfo.c:6)
==15377== by 0x80484EA: fun_c (inlinfo.c:14)
==15377== by 0x80484EA: fun_b (inlinfo.c:20)
==15377== by 0x80484EA: fun_a (inlinfo.c:26)
==15377== by 0x80484EA: main (inlinfo.c:33)
==15377==
==15377== Conditional jump or move depends on uninitialised value(s)
==15377== at 0x8048550: fun_d (inlinfo.c:6)
==15377== by 0x8048550: fun_noninline (inlinfo.c:41)
==15377== by 0x804850E: main (inlinfo.c:34)
==15377==
==15377== Conditional jump or move depends on uninitialised value(s)
==15377== at 0x8048520: fun_d (inlinfo.c:6)
==15377== by 0x8048520: main (inlinfo.c:35)

--read-var-info=<yes|no> [default: no]
When enabled, Valgrind will read information about variable types and
locations from DWARF3 debug info. This slows Valgrind startup signifi-
cantly and makes it use significantly more memory, but for the tools
that can take advantage of it (Memcheck, Helgrind, DRD) it can result
in more precise error messages. For example, here are some standard er-
rors issued by Memcheck:

==15363== Uninitialised byte(s) found during client check request
==15363== at 0x80484A9: croak (varinfo1.c:28)
==15363== by 0x8048544: main (varinfo1.c:55)
==15363== Address 0x80497f7 is 7 bytes inside data symbol "global_i2"
==15363==
==15363== Uninitialised byte(s) found during client check request
==15363== at 0x80484A9: croak (varinfo1.c:28)
==15363== by 0x8048550: main (varinfo1.c:56)
==15363== Address 0xbea0d0cc is on thread 1's stack
==15363== in frame #1, created by main (varinfo1.c:45)

And here are the same errors with --read-var-info=yes:

==15370== Uninitialised byte(s) found during client check request
==15370== at 0x80484A9: croak (varinfo1.c:28)
==15370== by 0x8048544: main (varinfo1.c:55)
==15370== Location 0x80497f7 is 0 bytes inside global_i2[7],
==15370== a global variable declared at varinfo1.c:41
==15370==
==15370== Uninitialised byte(s) found during client check request
==15370== at 0x80484A9: croak (varinfo1.c:28)
==15370== by 0x8048550: main (varinfo1.c:56)
==15370== Location 0xbeb4a0cc is 0 bytes inside local var "local"
==15370== declared at varinfo1.c:46, in frame #1 of thread 1

--vgdb-poll=<number> [default: 5000]
As part of its main loop, the Valgrind scheduler will poll to check if
some activity (such as an external command or some input from a gdb)
has to be handled by gdbserver. This activity poll will be done after
having run the given number of basic blocks (or slightly more than the
given number of basic blocks). This poll is quite cheap so the default
value is set relatively low. You might further decrease this value if
vgdb cannot use ptrace system call to interrupt Valgrind if all threads
are (most of the time) blocked in a system call.

--vgdb-shadow-registers=no|yes [default: no]
When activated, gdbserver will expose the Valgrind shadow registers to
GDB. With this, the value of the Valgrind shadow registers can be exam-
ined or changed using GDB. Exposing shadow registers only works with
GDB version 7.1 or later.

--vgdb-prefix=<prefix> [default: /tmp/vgdb-pipe]
To communicate with gdb/vgdb, the Valgrind gdbserver creates 3 files (2
named FIFOs and a mmap shared memory file). The prefix option controls
the directory and prefix for the creation of these files.

--run-libc-freeres=<yes|no> [default: yes]
This option is only relevant when running Valgrind on Linux with GNU
libc.

The GNU C library (libc.so), which is used by all programs, may allo-
cate memory for its own uses. Usually it doesn't bother to free that
memory when the program ends--there would be no point, since the Linux
kernel reclaims all process resources when a process exits anyway, so
it would just slow things down.

The glibc authors realised that this behaviour causes leak checkers,
such as Valgrind, to falsely report leaks in glibc, when a leak check
is done at exit. In order to avoid this, they provided a routine called
__libc_freeres specifically to make glibc release all memory it has al-
located. Memcheck therefore tries to run __libc_freeres at exit.

Unfortunately, in some very old versions of glibc, __libc_freeres is
sufficiently buggy to cause segmentation faults. This was particularly
noticeable on Red Hat 7.1. So this option is provided in order to in-
hibit the run of __libc_freeres. If your program seems to run fine on
Valgrind, but segfaults at exit, you may find that
--run-libc-freeres=no fixes that, although at the cost of possibly
falsely reporting space leaks in libc.so.

--run-cxx-freeres=<yes|no> [default: yes]
This option is only relevant when running Valgrind on Linux, FreeBSD or
Solaris C++ programs using libstdc++.

The GNU Standard C++ library (libstdc++.so), which is used by all C++
programs compiled with g++, may allocate memory for its own uses. Usu-
ally it doesn't bother to free that memory when the program ends--there
would be no point, since the kernel reclaims all process resources when
a process exits anyway, so it would just slow things down.

The gcc authors realised that this behaviour causes leak checkers, such
as Valgrind, to falsely report leaks in libstdc++, when a leak check is
done at exit. In order to avoid this, they provided a routine called
__gnu_cxx::__freeres specifically to make libstdc++ release all memory
it has allocated. Memcheck therefore tries to run __gnu_cxx::__freeres
at exit.

For the sake of flexibility and unforeseen problems with
__gnu_cxx::__freeres, option --run-cxx-freeres=no exists, although at
the cost of possibly falsely reporting space leaks in libstdc++.so.

--sim-hints=hint1,hint2,...
Pass miscellaneous hints to Valgrind which slightly modify the simu-
lated behaviour in nonstandard or dangerous ways, possibly to help the
simulation of strange features. By default no hints are enabled. Use
with caution! Currently known hints are:

* lax-ioctls: Be very lax about ioctl handling; the only assumption
is that the size is correct. Doesn't require the full buffer to be
initialised when writing. Without this, using some device drivers
with a large number of strange ioctl commands becomes very tire-
some.

* fuse-compatible: Enable special handling for certain system calls
that may block in a FUSE file-system. This may be necessary when
running Valgrind on a multi-threaded program that uses one thread
to manage a FUSE file-system and another thread to access that
file-system.

* enable-outer: Enable some special magic needed when the program be-
ing run is itself Valgrind.

* no-inner-prefix: Disable printing a prefix > in front of each std-
out or stderr output line in an inner Valgrind being run by an
outer Valgrind. This is useful when running Valgrind regression
tests in an outer/inner setup. Note that the prefix > will always
be printed in front of the inner debug logging lines.

* no-nptl-pthread-stackcache: This hint is only relevant when running
Valgrind on Linux; it is ignored on FreeBSD, Solaris and macOS.

The GNU glibc pthread library (libpthread.so), which is used by
pthread programs, maintains a cache of pthread stacks. When a
pthread terminates, the memory used for the pthread stack and some
thread local storage related data structure are not always directly
released. This memory is kept in a cache (up to a certain size),
and is re-used if a new thread is started.

This cache causes the helgrind tool to report some false positive
race condition errors on this cached memory, as helgrind does not
understand the internal glibc cache synchronisation primitives. So,
when using helgrind, disabling the cache helps to avoid false posi-
tive race conditions, in particular when using thread local storage
variables (e.g. variables using the __thread qualifier).

When using the memcheck tool, disabling the cache ensures the mem-
ory used by glibc to handle __thread variables is directly released
when a thread terminates.

Note: Valgrind disables the cache using some internal knowledge of
the glibc stack cache implementation and by examining the debug in-
formation of the pthread library. This technique is thus somewhat
fragile and might not work for all glibc versions. This has been
successfully tested with various glibc versions (e.g. 2.11, 2.16,
2.18) on various platforms.

* lax-doors: (Solaris only) Be very lax about door syscall handling
over unrecognised door file descriptors. Does not require that full
buffer is initialised when writing. Without this, programs using
libdoor(3LIB) functionality with completely proprietary semantics
may report large number of false positives.

* fallback-llsc: (MIPS and ARM64 only): Enables an alternative imple-
mentation of Load-Linked (LL) and Store-Conditional (SC) instruc-
tions. The standard implementation gives more correct behaviour,
but can cause indefinite looping on certain processor implementa-
tions that are intolerant of extra memory references between LL and
SC. So far this is known only to happen on Cavium 3 cores. You
should not need to use this flag, since the relevant cores are de-
tected at startup and the alternative implementation is automati-
cally enabled if necessary. There is no equivalent anti-flag: you
cannot force-disable the alternative implementation, if it is auto-
matically enabled. The underlying problem exists because the "stan-
dard" implementation of LL and SC is done by copying through LL and
SC instructions into the instrumented code. However, tools may in-
sert extra instrumentation memory references in between the LL and
SC instructions. These memory references are not present in the
original uninstrumented code, and their presence in the instru-
mented code can cause the SC instructions to persistently fail,
leading to indefinite looping in LL-SC blocks. The alternative im-
plementation gives correct behaviour of LL and SC instructions be-
tween threads in a process, up to and including the ABA scenario.
It also gives correct behaviour between a Valgrinded thread and a
non-Valgrinded thread running in a different process, that communi-
cate via shared memory, but only up to and including correct CAS
behaviour -- in this case the ABA scenario may not be correctly
handled.

--scheduling-quantum=<number> [default: 100000]
The --scheduling-quantum option controls the maximum number of basic
blocks executed by a thread before releasing the lock used by Valgrind
to serialise thread execution. Smaller values give finer interleaving
but increases the scheduling overhead. Finer interleaving can be useful
to reproduce race conditions with helgrind or DRD. For more details
about the Valgrind thread serialisation scheme and its impact on per-
formance and thread scheduling, see Scheduling and Multi-Thread Perfor-
mance.

--fair-sched=<no|yes|try> [default: no]
The --fair-sched option controls the locking mechanism used by Valgrind
to serialise thread execution. The locking mechanism controls the way
the threads are scheduled, and different settings give different
trade-offs between fairness and performance. For more details about the
Valgrind thread serialisation scheme and its impact on performance and
thread scheduling, see Scheduling and Multi-Thread Performance.

* The value --fair-sched=yes activates a fair scheduler. In short, if
multiple threads are ready to run, the threads will be scheduled in
a round robin fashion. This mechanism is not available on all plat-
forms or Linux versions. If not available, using --fair-sched=yes
will cause Valgrind to terminate with an error.

You may find this setting improves overall responsiveness if you
are running an interactive multithreaded program, for example a web
browser, on Valgrind.

* The value --fair-sched=try activates fair scheduling if available
on the platform. Otherwise, it will automatically fall back to
--fair-sched=no.

* The value --fair-sched=no activates a scheduler which does not
guarantee fairness between threads ready to run, but which in gen-
eral gives the highest performance.

--kernel-variant=variant1,variant2,...
Handle system calls and ioctls arising from minor variants of the de-
fault kernel for this platform. This is useful for running on hacked
kernels or with kernel modules which support nonstandard ioctls, for
example. Use with caution. If you don't understand what this option
does then you almost certainly don't need it. Currently known variants
are:

* bproc: support the sys_broc system call on x86. This is for running
on BProc, which is a minor variant of standard Linux which is some-
times used for building clusters.

* android-no-hw-tls: some versions of the Android emulator for ARM do
not provide a hardware TLS (thread-local state) register, and Val-
grind crashes at startup. Use this variant to select software sup-
port for TLS.

* android-gpu-sgx5xx: use this to support handling of proprietary
ioctls for the PowerVR SGX 5XX series of GPUs on Android devices.
Failure to select this does not cause stability problems, but may
cause Memcheck to report false errors after the program performs
GPU-specific ioctls.

* android-gpu-adreno3xx: similarly, use this to support handling of
proprietary ioctls for the Qualcomm Adreno 3XX series of GPUs on
Android devices.

--merge-recursive-frames=<number> [default: 0]
Some recursive algorithms, for example balanced binary tree implementa-
tions, create many different stack traces, each containing cycles of
calls. A cycle is defined as two identical program counter values sepa-
rated by zero or more other program counter values. Valgrind may then
use a lot of memory to store all these stack traces. This is a poor use
of memory considering that such stack traces contain repeated uninter-
esting recursive calls instead of more interesting information such as
the function that has initiated the recursive call.

The option --merge-recursive-frames=<number> instructs Valgrind to de-
tect and merge recursive call cycles having a size of up to <number>
frames. When such a cycle is detected, Valgrind records the cycle in
the stack trace as a unique program counter.

The value 0 (the default) causes no recursive call merging. A value of
1 will cause stack traces of simple recursive algorithms (for example,
a factorial implementation) to be collapsed. A value of 2 will usually
be needed to collapse stack traces produced by recursive algorithms
such as binary trees, quick sort, etc. Higher values might be needed
for more complex recursive algorithms.

Note: recursive calls are detected by analysis of program counter val-
ues. They are not detected by looking at function names.

--num-transtab-sectors=<number> [default: 6 for Android platforms, 16 for
all others]
Valgrind translates and instruments your program's machine code in
small fragments (basic blocks). The translations are stored in a trans-
lation cache that is divided into a number of sections (sectors). If
the cache is full, the sector containing the oldest translations is
emptied and reused. If these old translations are needed again, Val-
grind must re-translate and re-instrument the corresponding machine
code, which is expensive. If the "executed instructions" working set of
a program is big, increasing the number of sectors may improve perfor-
mance by reducing the number of re-translations needed. Sectors are al-
located on demand. Once allocated, a sector can never be freed, and oc-
cupies considerable space, depending on the tool and the value of
--avg-transtab-entry-size (about 40 MB per sector for Memcheck). Use
the option --stats=yes to obtain precise information about the memory
used by a sector and the allocation and recycling of sectors.

--avg-transtab-entry-size=<number> [default: 0, meaning use tool provided
default]
Average size of translated basic block. This average size is used to
dimension the size of a sector. Each tool provides a default value to
be used. If this default value is too small, the translation sectors
will become full too quickly. If this default value is too big, a sig-
nificant part of the translation sector memory will be unused. Note
that the average size of a basic block translation depends on the tool,
and might depend on tool options. For example, the memcheck option
--track-origins=yes increases the size of the basic block translations.
Use --avg-transtab-entry-size to tune the size of the sectors, either
to gain memory or to avoid too many retranslations.

--aspace-minaddr=<address> [default: depends on the platform]
To avoid potential conflicts with some system libraries, Valgrind does
not use the address space below --aspace-minaddr value, keeping it re-
served in case a library specifically requests memory in this region.
So, some "pessimistic" value is guessed by Valgrind depending on the
platform. On linux, by default, Valgrind avoids using the first 64MB
even if typically there is no conflict in this complete zone. You can
use the option --aspace-minaddr to have your memory hungry application
benefitting from more of this lower memory. On the other hand, if you
encounter a conflict, increasing aspace-minaddr value might solve it.
Conflicts will typically manifest themselves with mmap failures in the
low range of the address space. The provided address must be page
aligned and must be equal or bigger to 0x1000 (4KB). To find the de-
fault value on your platform, do something such as valgrind -d -d date
2>&1 | grep -i minaddr. Values lower than 0x10000 (64KB) are known to
create problems on some distributions.

--valgrind-stacksize=<number> [default: 1MB]
For each thread, Valgrind needs its own 'private' stack. The default
size for these stacks is largely dimensioned, and so should be suffi-
cient in most cases. In case the size is too small, Valgrind will seg-
fault. Before segfaulting, a warning might be produced by Valgrind when
approaching the limit.

Use the option --valgrind-stacksize if such an (unlikely) warning is
produced, or Valgrind dies due to a segmentation violation. Such seg-
mentation violations have been seen when demangling huge C++ symbols.

If your application uses many threads and needs a lot of memory, you
can gain some memory by reducing the size of these Valgrind stacks us-
ing the option --valgrind-stacksize.

--show-emwarns=<yes|no> [default: no]
When enabled, Valgrind will emit warnings about its CPU emulation in
certain cases. These are usually not interesting.

--require-text-symbol=:sonamepatt:fnnamepatt
When a shared object whose soname matches sonamepatt is loaded into the
process, examine all the text symbols it exports. If none of those
match fnnamepatt, print an error message and abandon the run. This
makes it possible to ensure that the run does not continue unless a
given shared object contains a particular function name.

Both sonamepatt and fnnamepatt can be written using the usual ? and *
wildcards. For example: ":*libc.so*:foo?bar". You may use characters
other than a colon to separate the two patterns. It is only important
that the first character and the separator character are the same. For
example, the above example could also be written "Q*libc.so*Qfoo?bar".
Multiple
--require-text-symbol flags are allowed, in which case shared objects
that are loaded into the process will be checked against all of them.

The purpose of this is to support reliable usage of marked-up li-
braries. For example, suppose we have a version of GCC's libgomp.so
which has been marked up with annotations to support Helgrind. It is
only too easy and confusing to load the wrong, un-annotated libgomp.so
into the application. So the idea is: add a text symbol in the
marked-up library, for example annotated_for_helgrind_3_6, and then
give the flag --require-text-symbol=:*libgomp*so*:annotated_for_hel-
grind_3_6 so that when libgomp.so is loaded, Valgrind scans its symbol
table, and if the symbol isn't present the run is aborted, rather than
continuing silently with the un-marked-up library. Note that you should
put the entire flag in quotes to stop shells expanding up the * and ?
wildcards.

--soname-synonyms=syn1=pattern1,syn2=pattern2,...
When a shared library is loaded, Valgrind checks for functions in the
library that must be replaced or wrapped. For example, Memcheck re-
places some string and memory functions (strchr, strlen, strcpy, mem-
chr, memcpy, memmove, etc.) with its own versions. Such replacements
are normally done only in shared libraries whose soname matches a pre-
defined soname pattern (e.g. libc.so* on linux). By default, no re-
placement is done for a statically linked binary or for alternative li-
braries, except for the allocation functions (malloc, free, calloc,
memalign, realloc, operator new, operator delete, etc.) Such allocation
functions are intercepted by default in any shared library or in the
executable if they are exported as global symbols. This means that if a
replacement allocation library such as tcmalloc is found, its functions
are also intercepted by default. In some cases, the replacements allow
--soname-synonyms to specify one additional synonym pattern, giving
flexibility in the replacement. Or to prevent interception of all pub-
lic allocation symbols.

Currently, this flexibility is only allowed for the malloc related
functions, using the synonym somalloc. This synonym is usable for all
tools doing standard replacement of malloc related functions (e.g. mem-
check, helgrind, drd, massif, dhat).

* Alternate malloc library: to replace the malloc related functions
in a specific alternate library with soname mymalloclib.so (and not
in any others), give the option --soname-synonyms=somalloc=mymallo-
clib.so. A pattern can be used to match multiple libraries sonames.
For example, --soname-synonyms=somalloc=*tcmalloc* will match the
soname of all variants of the tcmalloc library (native, debug, pro-
filed, ... tcmalloc variants).

Note: the soname of a elf shared library can be retrieved using the
readelf utility.

* Replacements in a statically linked library are done by using the
NONE pattern. For example, if you link with libtcmalloc.a, and only
want to intercept the malloc related functions in the executable
(and standard libraries) themselves, but not any other shared li-
braries, you can give the option --soname-synonyms=somalloc=NONE.
Note that a NONE pattern will match the main executable and any
shared library having no soname.

* To only intercept allocation symbols in the default system li-
braries, but not in any other shared library or the executable
defining public malloc or operator new related functions use a
non-existing library name like --soname-synonyms=somalloc=nouserin-
tercepts (where nouserintercepts can be any non-existing library
name).

* Shared library of the dynamic (runtime) linker is excluded from
searching for global public symbols, such as those for the malloc
related functions (identified by somalloc synonym).

--progress-interval=<number> [default: 0, meaning 'disabled']
This is an enhancement to Valgrind's debugging output. It is unlikely
to be of interest to end users.

When number is set to a non-zero value, Valgrind will print a one-line
progress summary every number seconds. Valid settings for number are
between 0 and 3600 inclusive. Here's some example output with number
set to 10:

PROGRESS: U 110s, W 113s, 97.3% CPU, EvC 414.79M, TIn 616.7k, TOut 0.5k, #thr 67
PROGRESS: U 120s, W 124s, 96.8% CPU, EvC 505.27M, TIn 636.6k, TOut 3.0k, #thr 64
PROGRESS: U 130s, W 134s, 97.0% CPU, EvC 574.90M, TIn 657.5k, TOut 3.0k, #thr 63

Each line shows:

* U: total user time

* W: total wallclock time

* CPU: overall average cpu use

* EvC: number of event checks. An event check is a backwards branch
in the simulated program, so this is a measure of forward progress
of the program

* TIn: number of code blocks instrumented by the JIT

* TOut: number of instrumented code blocks that have been thrown away

* #thr: number of threads in the program

From the progress of these, it is possible to observe:

* when the program is compute bound (TIn rises slowly, EvC rises
rapidly)

* when the program is in a spinloop (TIn/TOut fixed, EvC rises
rapidly)

* when the program is JIT-bound (TIn rises rapidly)

* when the program is rapidly discarding code (TOut rises rapidly)

* when the program is about to achieve some expected state (EvC ar-
rives at some value you expect)

* when the program is idling (U rises more slowly than W)

DEBUGGING VALGRIND OPTIONS
There are also some options for debugging Valgrind itself. You shouldn't
need to use them in the normal run of things. If you wish to see the list,
use the --help-debug option.

MEMCHECK OPTIONS
--leak-check=<no|summary|yes|full> [default: summary]
When enabled, search for memory leaks when the client program finishes.
If set to summary, it says how many leaks occurred. If set to full or
yes, each individual leak will be shown in detail and/or counted as an
error, as specified by the options --show-leak-kinds and --er-
rors-for-leak-kinds.

If --xml=yes is given, memcheck will automatically use the value
--leak-check=full. You can use --show-leak-kinds=none to reduce the
size of the xml output if you are not interested in the leak results.

--leak-resolution=<low|med|high> [default: high]
When doing leak checking, determines how willing Memcheck is to con-
sider different backtraces to be the same for the purposes of merging
multiple leaks into a single leak report. When set to low, only the
first two entries need match. When med, four entries have to match.
When high, all entries need to match.

For hardcore leak debugging, you probably want to use --leak-resolu-
tion=high together with --num-callers=40 or some such large number.

Note that the --leak-resolution setting does not affect Memcheck's
ability to find leaks. It only changes how the results are presented.

--show-leak-kinds=<set> [default: definite,possible]
Specifies the leak kinds to show in a full leak search, in one of the
following ways:

* a comma separated list of one or more of definite indirect possible
reachable.

* all to specify the complete set (all leak kinds). It is equivalent
to --show-leak-kinds=definite,indirect,possible,reachable.

* none for the empty set.

--errors-for-leak-kinds=<set> [default: definite,possible]
Specifies the leak kinds to count as errors in a full leak search. The
<set> is specified similarly to --show-leak-kinds

--leak-check-heuristics=<set> [default: all]
Specifies the set of leak check heuristics to be used during leak
searches. The heuristics control which interior pointers to a block
cause it to be considered as reachable. The heuristic set is specified
in one of the following ways:

* a comma separated list of one or more of stdstring length64 newar-
ray multipleinheritance.

* all to activate the complete set of heuristics. It is equivalent to
--leak-check-heuristics=stdstring,length64,newarray,multipleinheri-
tance.

* none for the empty set.

Note that these heuristics are dependent on the layout of the objects
produced by the C++ compiler. They have been tested with some gcc ver-
sions (e.g. 4.4 and 4.7). They might not work properly with other C++
compilers.

--show-reachable=<yes|no> , --show-possibly-lost=<yes|no>
These options provide an alternative way to specify the leak kinds to
show:

* --show-reachable=no --show-possibly-lost=yes is equivalent to
--show-leak-kinds=definite,possible.

* --show-reachable=no --show-possibly-lost=no is equivalent to
--show-leak-kinds=definite.

* --show-reachable=yes is equivalent to --show-leak-kinds=all.

Note that --show-possibly-lost=no has no effect if --show-reachable=yes
is specified.

--xtree-leak=<no|yes> [no]
If set to yes, the results for the leak search done at exit will be
output in a 'Callgrind Format' execution tree file. Note that this au-
tomatically sets the options --leak-check=full and
--show-leak-kinds=all, to allow xtree visualisation tools such as
kcachegrind to select what kind to leak to visualize. The produced file
will contain the following events:

* RB : Reachable Bytes

* PB : Possibly lost Bytes

* IB : Indirectly lost Bytes

* DB : Definitely lost Bytes (direct plus indirect)

* DIB : Definitely Indirectly lost Bytes (subset of DB)

* RBk : reachable Blocks

* PBk : Possibly lost Blocks

* IBk : Indirectly lost Blocks

* DBk : Definitely lost Blocks

The increase or decrease for all events above will also be output in
the file to provide the delta (increase or decrease) between 2 succes-
sive leak searches. For example, iRB is the increase of the RB event,
dPBk is the decrease of PBk event. The values for the increase and de-
crease events will be zero for the first leak search done.

See Execution Trees for a detailed explanation about execution trees.

--xtree-leak-file=<filename> [default: xtleak.kcg.%p]
Specifies that Valgrind should produce the xtree leak report in the
specified file. Any %p, %q or %n sequences appearing in the filename
are expanded in exactly the same way as they are for --log-file. See
the description of --log-file for details.

See Execution Trees for a detailed explanation about execution trees
formats.

--undef-value-errors=<yes|no> [default: yes]
Controls whether Memcheck reports uses of undefined value errors. Set
this to no if you don't want to see undefined value errors. It also has
the side effect of speeding up Memcheck somewhat. AddrCheck (removed in
Valgrind 3.1.0) functioned like Memcheck with --undef-value-errors=no.

--track-origins=<yes|no> [default: no]
Controls whether Memcheck tracks the origin of uninitialised values. By
default, it does not, which means that although it can tell you that an
uninitialised value is being used in a dangerous way, it cannot tell
you where the uninitialised value came from. This often makes it diffi-
cult to track down the root problem.

When set to yes, Memcheck keeps track of the origins of all unini-
tialised values. Then, when an uninitialised value error is reported,
Memcheck will try to show the origin of the value. An origin can be one
of the following four places: a heap block, a stack allocation, a
client request, or miscellaneous other sources (eg, a call to brk).

For uninitialised values originating from a heap block, Memcheck shows
where the block was allocated. For uninitialised values originating
from a stack allocation, Memcheck can tell you which function allocated
the value, but no more than that -- typically it shows you the source
location of the opening brace of the function. So you should carefully
check that all of the function's local variables are initialised prop-
erly.

Performance overhead: origin tracking is expensive. It halves Mem-
check's speed and increases memory use by a minimum of 100MB, and pos-
sibly more. Nevertheless it can drastically reduce the effort required
to identify the root cause of uninitialised value errors, and so is of-
ten a programmer productivity win, despite running more slowly.

Accuracy: Memcheck tracks origins quite accurately. To avoid very large
space and time overheads, some approximations are made. It is possible,
although unlikely, that Memcheck will report an incorrect origin, or
not be able to identify any origin.

Note that the combination --track-origins=yes and --undef-value-er-
rors=no is nonsensical. Memcheck checks for and rejects this combina-
tion at startup.

--partial-loads-ok=<yes|no> [default: yes]
Controls how Memcheck handles 32-, 64-, 128- and 256-bit naturally
aligned loads from addresses for which some bytes are addressable and
others are not. When yes, such loads do not produce an address error.
Instead, loaded bytes originating from illegal addresses are marked as
uninitialised, and those corresponding to legal addresses are handled
in the normal way.

When no, loads from partially invalid addresses are treated the same as
loads from completely invalid addresses: an illegal-address error is
issued, and the resulting bytes are marked as initialised.

Note that code that behaves in this way is in violation of the ISO
C/C++ standards, and should be considered broken. If at all possible,
such code should be fixed.

--expensive-definedness-checks=<no|auto|yes> [default: auto]
Controls whether Memcheck should employ more precise but also more ex-
pensive (time consuming) instrumentation when checking the definedness
of certain values. In particular, this affects the instrumentation of
integer adds, subtracts and equality comparisons.

Selecting --expensive-definedness-checks=yes causes Memcheck to use the
most accurate analysis possible. This minimises false error rates but
can cause up to 30% performance degradation.

Selecting --expensive-definedness-checks=no causes Memcheck to use the
cheapest instrumentation possible. This maximises performance but will
normally give an unusably high false error rate.

The default setting, --expensive-definedness-checks=auto, is strongly
recommended. This causes Memcheck to use the minimum of expensive in-
strumentation needed to achieve the same false error rate as --expen-
sive-definedness-checks=yes. It also enables an instrumentation-time
analysis pass which aims to further reduce the costs of accurate in-
strumentation. Overall, the performance loss is generally around 5%
relative to --expensive-definedness-checks=no, although this is
strongly workload dependent. Note that the exact instrumentation set-
tings in this mode are architecture dependent.

--keep-stacktraces=alloc|free|alloc-and-free|alloc-then-free|none [default:
alloc-and-free]
Controls which stack trace(s) to keep for malloc'd and/or free'd
blocks.

With alloc-then-free, a stack trace is recorded at allocation time, and
is associated with the block. When the block is freed, a second stack
trace is recorded, and this replaces the allocation stack trace. As a
result, any "use after free" errors relating to this block can only
show a stack trace for where the block was freed.

With alloc-and-free, both allocation and the deallocation stack traces
for the block are stored. Hence a "use after free" error will show
both, which may make the error easier to diagnose. Compared to al-
loc-then-free, this setting slightly increases Valgrind's memory use as
the block contains two references instead of one.

With alloc, only the allocation stack trace is recorded (and reported).
With free, only the deallocation stack trace is recorded (and re-
ported). These values somewhat decrease Valgrind's memory and cpu us-
age. They can be useful depending on the error types you are searching
for and the level of detail you need to analyse them. For example, if
you are only interested in memory leak errors, it is sufficient to
record the allocation stack traces.

With none, no stack traces are recorded for malloc and free operations.
If your program allocates a lot of blocks and/or allocates/frees from
many different stack traces, this can significantly decrease cpu and/or
memory required. Of course, few details will be reported for errors re-
lated to heap blocks.

Note that once a stack trace is recorded, Valgrind keeps the stack
trace in memory even if it is not referenced by any block. Some pro-
grams (for example, recursive algorithms) can generate a huge number of
stack traces. If Valgrind uses too much memory in such circumstances,
you can reduce the memory required with the options --keep-stacktraces
and/or by using a smaller value for the option --num-callers.

If you want to use --xtree-memory=full memory profiling (see Execution
Trees), then you cannot specify --keep-stacktraces=free or
--keep-stacktraces=none.

--freelist-vol=<number> [default: 20000000]
When the client program releases memory using free (in C) or delete
(C++), that memory is not immediately made available for re-allocation.
Instead, it is marked inaccessible and placed in a queue of freed
blocks. The purpose is to defer as long as possible the point at which
freed-up memory comes back into circulation. This increases the chance
that Memcheck will be able to detect invalid accesses to blocks for
some significant period of time after they have been freed.

This option specifies the maximum total size, in bytes, of the blocks
in the queue. The default value is twenty million bytes. Increasing
this increases the total amount of memory used by Memcheck but may de-
tect invalid uses of freed blocks which would otherwise go undetected.

--freelist-big-blocks=<number> [default: 1000000]
When making blocks from the queue of freed blocks available for re-al-
location, Memcheck will in priority re-circulate the blocks with a size
greater or equal to --freelist-big-blocks. This ensures that freeing
big blocks (in particular freeing blocks bigger than --freelist-vol)
does not immediately lead to a re-circulation of all (or a lot of) the
small blocks in the free list. In other words, this option increases
the likelihood to discover dangling pointers for the "small" blocks,
even when big blocks are freed.

Setting a value of 0 means that all the blocks are re-circulated in a
FIFO order.

--workaround-gcc296-bugs=<yes|no> [default: no]
When enabled, assume that reads and writes some small distance below
the stack pointer are due to bugs in GCC 2.96, and does not report
them. The "small distance" is 256 bytes by default. Note that GCC 2.96
is the default compiler on some ancient Linux distributions (RedHat
7.X) and so you may need to use this option. Do not use it if you do
not have to, as it can cause real errors to be overlooked. A better al-
ternative is to use a more recent GCC in which this bug is fixed.

You may also need to use this option when working with GCC 3.X or 4.X
on 32-bit PowerPC Linux. This is because GCC generates code which occa-
sionally accesses below the stack pointer, particularly for float-
ing-point to/from integer conversions. This is in violation of the
32-bit PowerPC ELF specification, which makes no provision for loca-
tions below the stack pointer to be accessible.

This option is deprecated as of version 3.12 and may be removed from
future versions. You should instead use --ignore-range-below-sp to
specify the exact range of offsets below the stack pointer that should
be ignored. A suitable equivalent is --ignore-range-below-sp=1024-1.

--ignore-range-below-sp=<number>-<number>
This is a more general replacement for the deprecated
--workaround-gcc296-bugs option. When specified, it causes Memcheck not
to report errors for accesses at the specified offsets below the stack
pointer. The two offsets must be positive decimal numbers and -- some-
what counterintuitively -- the first one must be larger, in order to
imply a non-wraparound address range to ignore. For example, to ignore
4 byte accesses at 8192 bytes below the stack pointer, use --ig-
nore-range-below-sp=8192-8189. Only one range may be specified.

--show-mismatched-frees=<yes|no> [default: yes]
When enabled, Memcheck checks that heap blocks are deallocated using a
function that matches the allocating function. That is, it expects free
to be used to deallocate blocks allocated by malloc, delete for blocks
allocated by new, and delete[] for blocks allocated by new[]. If a mis-
match is detected, an error is reported. This is in general important
because in some environments, freeing with a non-matching function can
cause crashes.

There is however a scenario where such mismatches cannot be avoided.
That is when the user provides implementations of new/new[] that call
malloc and of delete/delete[] that call free, and these functions are
asymmetrically inlined. For example, imagine that delete[] is inlined
but new[] is not. The result is that Memcheck "sees" all delete[] calls
as direct calls to free, even when the program source contains no mis-
matched calls.

This causes a lot of confusing and irrelevant error reports.
--show-mismatched-frees=no disables these checks. It is not generally
advisable to disable them, though, because you may miss real errors as
a result.

--show-realloc-size-zero=<yes|no> [default: yes]
When enabled, Memcheck checks for uses of realloc with a size of zero.
This usage of realloc is unsafe since it is not portable. On some sys-
tems it will behave like free. On other systems it will either do noth-
ing or else behave like a call to free followed by a call to malloc
with a size of zero.

--ignore-ranges=0xPP-0xQQ[,0xRR-0xSS]
Any ranges listed in this option (and multiple ranges can be specified,
separated by commas) will be ignored by Memcheck's addressability
checking.

--malloc-fill=<hexnumber>
Fills blocks allocated by malloc, new, etc, but not by calloc, with the
specified byte. This can be useful when trying to shake out obscure
memory corruption problems. The allocated area is still regarded by
Memcheck as undefined -- this option only affects its contents. Note
that --malloc-fill does not affect a block of memory when it is used as
argument to client requests VALGRIND_MEMPOOL_ALLOC or VALGRIND_MALLO-
CLIKE_BLOCK.

--free-fill=<hexnumber>
Fills blocks freed by free, delete, etc, with the specified byte value.
This can be useful when trying to shake out obscure memory corruption
problems. The freed area is still regarded by Memcheck as not valid for
access -- this option only affects its contents. Note that --free-fill
does not affect a block of memory when it is used as argument to client
requests VALGRIND_MEMPOOL_FREE or VALGRIND_FREELIKE_BLOCK.

CACHEGRIND OPTIONS
--cachegrind-out-file=<file>
Write the Cachegrind output file to file rather than to the default
output file, cachegrind.out.<pid>. The %p and %q format specifiers can
be used to embed the process ID and/or the contents of an environment
variable in the name, as is the case for the core option --log-file.

--cache-sim=no|yes [no]
Enables or disables collection of cache access and miss counts.

--branch-sim=no|yes [no]
Enables or disables collection of branch instruction and misprediction
counts.

--instr-at-start=no|yes [yes]
Enables or disables instrumentation at the start of execution. Use this
in combination with CACHEGRIND_START_INSTRUMENTATION and
CACHEGRIND_STOP_INSTRUMENTATION to measure only part of a client pro-
gram's execution.

--I1=<size>,<associativity>,<line size>
Specify the size, associativity and line size of the level 1 instruc-
tion cache. Only useful with --cache-sim=yes.

--D1=<size>,<associativity>,<line size>
Specify the size, associativity and line size of the level 1 data
cache. Only useful with --cache-sim=yes.

--LL=<size>,<associativity>,<line size>
Specify the size, associativity and line size of the last-level cache.
Only useful with --cache-sim=yes.

CALLGRIND OPTIONS
--callgrind-out-file=<file>
Write the profile data to file rather than to the default output file,
callgrind.out.<pid>. The %p and %q format specifiers can be used to em-
bed the process ID and/or the contents of an environment variable in
the name, as is the case for the core option --log-file. When multiple
dumps are made, the file name is modified further; see below.

--dump-line=<no|yes> [default: yes]
This specifies that event counting should be performed at source line
granularity. This allows source annotation for sources which are com-
piled with debug information (-g).

--dump-instr=<no|yes> [default: no]
This specifies that event counting should be performed at per-instruc-
tion granularity. This allows for assembly code annotation. Currently
the results can only be displayed by KCachegrind.

--compress-strings=<no|yes> [default: yes]
This option influences the output format of the profile data. It speci-
fies whether strings (file and function names) should be identified by
numbers. This shrinks the file, but makes it more difficult for humans
to read (which is not recommended in any case).

--compress-pos=<no|yes> [default: yes]
This option influences the output format of the profile data. It speci-
fies whether numerical positions are always specified as absolute val-
ues or are allowed to be relative to previous numbers. This shrinks the
file size.

--combine-dumps=<no|yes> [default: no]
When enabled, when multiple profile data parts are to be generated
these parts are appended to the same output file. Not recommended.

--dump-every-bb=<count> [default: 0, never]
Dump profile data every count basic blocks. Whether a dump is needed is
only checked when Valgrind's internal scheduler is run. Therefore, the
minimum setting useful is about 100000. The count is a 64-bit value to
make long dump periods possible.

--dump-before=<function>
Dump when entering function.

--zero-before=<function>
Zero all costs when entering function.

--dump-after=<function>
Dump when leaving function.

--instr-atstart=<yes|no> [default: yes]
Specify if you want Callgrind to start simulation and profiling from
the beginning of the program. When set to no, Callgrind will not be
able to collect any information, including calls, but it will have at
most a slowdown of around 4, which is the minimum Valgrind overhead.
Instrumentation can be interactively enabled via callgrind_control -i
on.

Note that the resulting call graph will most probably not contain main,
but will contain all the functions executed after instrumentation was
enabled. Instrumentation can also be programmatically enabled/disabled.
See the Callgrind include file callgrind.h for the macro you have to
use in your source code.

For cache simulation, results will be less accurate when switching on
instrumentation later in the program run, as the simulator starts with
an empty cache at that moment. Switch on event collection later to cope
with this error.

--collect-atstart=<yes|no> [default: yes]
Specify whether event collection is enabled at beginning of the profile
run.

To only look at parts of your program, you have two possibilities:

1. Zero event counters before entering the program part you want to
profile, and dump the event counters to a file after leaving that
program part.

2. Switch on/off collection state as needed to only see event counters
happening while inside of the program part you want to profile.

The second option can be used if the program part you want to profile
is called many times. Option 1, i.e. creating a lot of dumps is not
practical here.

Collection state can be toggled at entry and exit of a given function
with the option --toggle-collect. If you use this option, collection
state should be disabled at the beginning. Note that the specification
of --toggle-collect implicitly sets --collect-state=no.

Collection state can be toggled also by inserting the client request
CALLGRIND_TOGGLE_COLLECT ; at the needed code positions.

--toggle-collect=<function>
Toggle collection on entry/exit of function.

--collect-jumps=<no|yes> [default: no]
This specifies whether information for (conditional) jumps should be
collected. As above, callgrind_annotate currently is not able to show
you the data. You have to use KCachegrind to get jump arrows in the an-
notated code.

--collect-systime=<no|yes|msec|usec|nsec> [default: no]
This specifies whether information for system call times should be col-
lected.

The value no indicates to record no system call information.

The other values indicate to record the number of system calls done
(sysCount event) and the elapsed time (sysTime event) spent in system
calls. The --collect-systime value gives the unit used for sysTime :
milli seconds, micro seconds or nano seconds. With the value nsec,
callgrind also records the cpu time spent during system calls
(sysCpuTime).

The value yes is a synonym of msec. The value nsec is not supported on
Darwin.

--collect-bus=<no|yes> [default: no]
This specifies whether the number of global bus events executed should
be collected. The event type "Ge" is used for these events.

--cache-sim=<yes|no> [default: no]
Specify if you want to do full cache simulation. By default, only in-
struction read accesses will be counted ("Ir"). With cache simulation,
further event counters are enabled: Cache misses on instruction reads
("I1mr"/"ILmr"), data read accesses ("Dr") and related cache misses
("D1mr"/"DLmr"), data write accesses ("Dw") and related cache misses
("D1mw"/"DLmw"). For more information, see Cachegrind: a cache and
branch-prediction profiler.

--branch-sim=<yes|no> [default: no]
Specify if you want to do branch prediction simulation. Further event
counters are enabled: Number of executed conditional branches and re-
lated predictor misses ("Bc"/"Bcm"), executed indirect jumps and re-
lated misses of the jump address predictor ("Bi"/"Bim").

HELGRIND OPTIONS
--free-is-write=no|yes [default: no]
When enabled (not the default), Helgrind treats freeing of heap memory
as if the memory was written immediately before the free. This exposes
races where memory is referenced by one thread, and freed by another,
but there is no observable synchronisation event to ensure that the
reference happens before the free.

This functionality is new in Valgrind 3.7.0, and is regarded as experi-
mental. It is not enabled by default because its interaction with cus-
tom memory allocators is not well understood at present. User feedback
is welcomed.

--track-lockorders=no|yes [default: yes]
When enabled (the default), Helgrind performs lock order consistency
checking. For some buggy programs, the large number of lock order er-
rors reported can become annoying, particularly if you're only inter-
ested in race errors. You may therefore find it helpful to disable lock
order checking.

--history-level=none|approx|full [default: full]
--history-level=full (the default) causes Helgrind collects enough in-
formation about "old" accesses that it can produce two stack traces in
a race report -- both the stack trace for the current access, and the
trace for the older, conflicting access. To limit memory usage, "old"
accesses stack traces are limited to a maximum of --history-back-
trace-size entries (default 8) or to --num-callers value if this value
is smaller.

Collecting such information is expensive in both speed and memory, par-
ticularly for programs that do many inter-thread synchronisation events
(locks, unlocks, etc). Without such information, it is more difficult
to track down the root causes of races. Nonetheless, you may not need
it in situations where you just want to check for the presence or ab-
sence of races, for example, when doing regression testing of a previ-
ously race-free program.

--history-level=none is the opposite extreme. It causes Helgrind not to
collect any information about previous accesses. This can be dramati-
cally faster than --history-level=full.

--history-level=approx provides a compromise between these two ex-
tremes. It causes Helgrind to show a full trace for the later access,
and approximate information regarding the earlier access. This approxi-
mate information consists of two stacks, and the earlier access is
guaranteed to have occurred somewhere between program points denoted by
the two stacks. This is not as useful as showing the exact stack for
the previous access (as --history-level=full does), but it is better
than nothing, and it is almost as fast as --history-level=none.

--history-backtrace-size=<number> [default: 8]
When --history-level=full is selected, --history-backtrace-size=number
indicates how many entries to record in "old" accesses stack traces.

--delta-stacktrace=no|yes [default: yes on linux amd64/x86]
This flag only has any effect at --history-level=full.

--delta-stacktrace configures the way Helgrind captures the stacktraces
for the option --history-level=full. Such a stacktrace is typically
needed each time a new piece of memory is read or written in a basic
block of instructions.

--delta-stacktrace=no causes Helgrind to compute a full history stack-
trace from the unwind info each time a stacktrace is needed.

--delta-stacktrace=yes indicates to Helgrind to derive a new stacktrace
from the previous stacktrace, as long as there was no call instruction,
no return instruction, or any other instruction changing the call stack
since the previous stacktrace was captured. If no such instruction was
executed, the new stacktrace can be derived from the previous stack-
trace by just changing the top frame to the current program counter.
This option can speed up Helgrind by 25% when using --his-
tory-level=full.

The following aspects have to be considered when using --delta-stack-
trace=yes :

* In some cases (for example in a function prologue), the valgrind
unwinder might not properly unwind the stack, due to some limita-
tions and/or due to wrong unwind info. When using --delta-stack-
trace=yes, the wrong stack trace captured in the function prologue
will be kept till the next call or return.

* On the other hand, --delta-stacktrace=yes sometimes helps to obtain
a correct stacktrace, for example when the unwind info allows a
correct stacktrace to be done in the beginning of the sequence, but
not later on in the instruction sequence.

* Determining which instructions are changing the callstack is par-
tially based on platform dependent heuristics, which have to be
tuned/validated specifically for the platform. Also, unwinding in a
function prologue must be good enough to allow using --delta-stack-
trace=yes. Currently, the option --delta-stacktrace=yes has been
reasonably validated only on linux x86 32 bits and linux amd64 64
bits. For more details about how to validate --delta-stack-
trace=yes, see debug option --hg-sanity-flags and the function
check_cached_rcec_ok in libhb_core.c.

--conflict-cache-size=N [default: 1000000]
This flag only has any effect at --history-level=full.

Information about "old" conflicting accesses is stored in a cache of
limited size, with LRU-style management. This is necessary because it
isn't practical to store a stack trace for every single memory access
made by the program. Historical information on not recently accessed
locations is periodically discarded, to free up space in the cache.

This option controls the size of the cache, in terms of the number of
different memory addresses for which conflicting access information is
stored. If you find that Helgrind is showing race errors with only one
stack instead of the expected two stacks, try increasing this value.

The minimum value is 10,000 and the maximum is 30,000,000 (thirty times
the default value). Increasing the value by 1 increases Helgrind's mem-
ory requirement by very roughly 100 bytes, so the maximum value will
easily eat up three extra gigabytes or so of memory.

--check-stack-refs=no|yes [default: yes]
By default Helgrind checks all data memory accesses made by your pro-
gram. This flag enables you to skip checking for accesses to thread
stacks (local variables). This can improve performance, but comes at
the cost of missing races on stack-allocated data.

--ignore-thread-creation=<yes|no> [default: no]
Controls whether all activities during thread creation should be ig-
nored. By default enabled only on Solaris. Solaris provides higher
throughput, parallelism and scalability than other operating systems,
at the cost of more fine-grained locking activity. This means for exam-
ple that when a thread is created under glibc, just one big lock is
used for all thread setup. Solaris libc uses several fine-grained locks
and the creator thread resumes its activities as soon as possible,
leaving for example stack and TLS setup sequence to the created thread.
This situation confuses Helgrind as it assumes there is some false or-
dering in place between creator and created thread; and therefore many
types of race conditions in the application would not be reported. To
prevent such false ordering, this command line option is set to yes by
default on Solaris. All activity (loads, stores, client requests) is
therefore ignored during:

* pthread_create() call in the creator thread

* thread creation phase (stack and TLS setup) in the created thread

Also new memory allocated during thread creation is untracked, that is
race reporting is suppressed there. DRD does the same thing implicitly.
This is necessary because Solaris libc caches many objects and reuses
them for different threads and that confuses Helgrind.

DRD OPTIONS
--check-stack-var=<yes|no> [default: no]
Controls whether DRD detects data races on stack variables. Verifying
stack variables is disabled by default because most programs do not
share stack variables over threads.

--exclusive-threshold=<n> [default: off]
Print an error message if any mutex or writer lock has been held longer
than the time specified in milliseconds. This option enables the detec-
tion of lock contention.

--join-list-vol=<n> [default: 10]
Data races that occur between a statement at the end of one thread and
another thread can be missed if memory access information is discarded
immediately after a thread has been joined. This option allows one to
specify for how many joined threads memory access information should be
retained.

--first-race-only=<yes|no> [default: no]
Whether to report only the first data race that has been detected on a
memory location or all data races that have been detected on a memory
location.

--free-is-write=<yes|no> [default: no]
Whether to report races between accessing memory and freeing memory.
Enabling this option may cause DRD to run slightly slower. Notes:

* Don't enable this option when using custom memory allocators that
use the VG_USERREQ__MALLOCLIKE_BLOCK and VG_USERREQ__FREELIKE_BLOCK
because that would result in false positives.

* Don't enable this option when using reference-counted objects be-
cause that will result in false positives, even when that code has
been annotated properly with ANNOTATE_HAPPENS_BEFORE and ANNO-
TATE_HAPPENS_AFTER. See e.g. the output of the following command
for an example: valgrind --tool=drd --free-is-write=yes
drd/tests/annotate_smart_pointer.

--report-signal-unlocked=<yes|no> [default: yes]
Whether to report calls to pthread_cond_signal and pthread_cond_broad-
cast where the mutex associated with the signal through
pthread_cond_wait or pthread_cond_timed_waitis not locked at the time
the signal is sent. Sending a signal without holding a lock on the as-
sociated mutex is a common programming error which can cause subtle
race conditions and unpredictable behavior. There exist some uncommon
synchronization patterns however where it is safe to send a signal
without holding a lock on the associated mutex.

--segment-merging=<yes|no> [default: yes]
Controls segment merging. Segment merging is an algorithm to limit mem-
ory usage of the data race detection algorithm. Disabling segment merg-
ing may improve the accuracy of the so-called 'other segments' dis-
played in race reports but can also trigger an out of memory error.

--segment-merging-interval=<n> [default: 10]
Perform segment merging only after the specified number of new segments
have been created. This is an advanced configuration option that allows
one to choose whether to minimize DRD's memory usage by choosing a low
value or to let DRD run faster by choosing a slightly higher value. The
optimal value for this parameter depends on the program being analyzed.
The default value works well for most programs.

--shared-threshold=<n> [default: off]
Print an error message if a reader lock has been held longer than the
specified time (in milliseconds). This option enables the detection of
lock contention.

--show-confl-seg=<yes|no> [default: yes]
Show conflicting segments in race reports. Since this information can
help to find the cause of a data race, this option is enabled by de-
fault. Disabling this option makes the output of DRD more compact.

--show-stack-usage=<yes|no> [default: no]
Print stack usage at thread exit time. When a program creates a large
number of threads it becomes important to limit the amount of virtual
memory allocated for thread stacks. This option makes it possible to
observe how much stack memory has been used by each thread of the
client program. Note: the DRD tool itself allocates some temporary data
on the client thread stack. The space necessary for this temporary data
must be allocated by the client program when it allocates stack memory,
but is not included in stack usage reported by DRD.

--ignore-thread-creation=<yes|no> [default: no]
Controls whether all activities during thread creation should be ig-
nored. By default enabled only on Solaris. Solaris provides higher
throughput, parallelism and scalability than other operating systems,
at the cost of more fine-grained locking activity. This means for exam-
ple that when a thread is created under glibc, just one big lock is
used for all thread setup. Solaris libc uses several fine-grained locks
and the creator thread resumes its activities as soon as possible,
leaving for example stack and TLS setup sequence to the created thread.
This situation confuses DRD as it assumes there is some false ordering
in place between creator and created thread; and therefore many types
of race conditions in the application would not be reported. To prevent
such false ordering, this command line option is set to yes by default
on Solaris. All activity (loads, stores, client requests) is therefore
ignored during:

* pthread_create() call in the creator thread

* thread creation phase (stack and TLS setup) in the created thread

--trace-addr=<address> [default: none]
Trace all load and store activity for the specified address. This op-
tion may be specified more than once.

--ptrace-addr=<address> [default: none]
Trace all load and store activity for the specified address and keep
doing that even after the memory at that address has been freed and re-
allocated.

--trace-alloc=<yes|no> [default: no]
Trace all memory allocations and deallocations. May produce a huge
amount of output.

--trace-barrier=<yes|no> [default: no]
Trace all barrier activity.

--trace-cond=<yes|no> [default: no]
Trace all condition variable activity.

--trace-fork-join=<yes|no> [default: no]
Trace all thread creation and all thread termination events.

--trace-hb=<yes|no> [default: no]
Trace execution of the ANNOTATE_HAPPENS_BEFORE(), ANNOTATE_HAPPENS_AF-
TER() and ANNOTATE_HAPPENS_DONE() client requests.

--trace-mutex=<yes|no> [default: no]
Trace all mutex activity.

--trace-rwlock=<yes|no> [default: no]
Trace all reader-writer lock activity.

--trace-semaphore=<yes|no> [default: no]
Trace all semaphore activity.

MASSIF OPTIONS
--heap=<yes|no> [default: yes]
Specifies whether heap profiling should be done.

--heap-admin=<size> [default: 8]
If heap profiling is enabled, gives the number of administrative bytes
per block to use. This should be an estimate of the average, since it
may vary. For example, the allocator used by glibc on Linux requires
somewhere between 4 to 15 bytes per block, depending on various fac-
tors. That allocator also requires admin space for freed blocks, but
Massif cannot account for this.

--stacks=<yes|no> [default: no]
Specifies whether stack profiling should be done. This option slows
Massif down greatly, and so is off by default. Note that Massif assumes
that the main stack has size zero at start-up. This is not true, but
doing otherwise accurately is difficult. Furthermore, starting at zero
better indicates the size of the part of the main stack that a user
program actually has control over.

If you give at least 4 -v verbosity arguments, then massif produces a
trace for each stack increase and decrease. The stack increase trace
contains the IP address that increased the stack. Note that to get
fully precise IP address, you must specify the options -px-default=un-
windregs-at-mem-access --px-file-backed=unwindregs-at-mem-access.

--pages-as-heap=<yes|no> [default: no]
Tells Massif to profile memory at the page level rather than at the
malloc'd block level. See above for details.

--depth=<number> [default: 30]
Maximum depth of the allocation trees recorded for detailed snapshots.
Increasing it will make Massif run somewhat more slowly, use more mem-
ory, and produce bigger output files.

--alloc-fn=<name>
Functions specified with this option will be treated as though they
were a heap allocation function such as malloc. This is useful for
functions that are wrappers to malloc or new, which can fill up the al-
location trees with uninteresting information. This option can be spec-
ified multiple times on the command line, to name multiple functions.

Note that the named function will only be treated this way if it is the
top entry in a stack trace, or just below another function treated this
way. For example, if you have a function malloc1 that wraps malloc, and
malloc2 that wraps malloc1, just specifying --alloc-fn=malloc2 will
have no effect. You need to specify --alloc-fn=malloc1 as well. This is
a little inconvenient, but the reason is that checking for allocation
functions is slow, and it saves a lot of time if Massif can stop look-
ing through the stack trace entries as soon as it finds one that
doesn't match rather than having to continue through all the entries.

Note that C++ names are demangled. Note also that overloaded C++ names
must be written in full. Single quotes may be necessary to prevent the
shell from breaking them up. For example:

--alloc-fn='operator new(unsigned, std::nothrow_t const&)'

Arguments of type size_t need to be replaced with unsigned long on
64bit platforms and unsigned on 32bit platforms.

--alloc-fn will work with inline functions. Inline function names are
not mangled, which means that you only need to provide the function
name and not the argument list.

--alloc-fn does not support wildcards.

--ignore-fn=<name>
Any direct heap allocation (i.e. a call to malloc, new, etc, or a call
to a function named by an --alloc-fn option) that occurs in a function
specified by this option will be ignored. This is mostly useful for
testing purposes. This option can be specified multiple times on the
command line, to name multiple functions.

Any realloc of an ignored block will also be ignored, even if the real-
loc call does not occur in an ignored function. This avoids the possi-
bility of negative heap sizes if ignored blocks are shrunk with real-
loc.

The rules for writing C++ function names are the same as for --alloc-fn
above.

--threshold=<m.n> [default: 1.0]
The significance threshold for heap allocations, as a percentage of to-
tal memory size. Allocation tree entries that account for less than
this will be aggregated. Note that this should be specified in tandem
with ms_print's option of the same name.

--peak-inaccuracy=<m.n> [default: 1.0]
Massif does not necessarily record the actual global memory allocation
peak; by default it records a peak only when the global memory alloca-
tion size exceeds the previous peak by at least 1.0%. This is because
there can be many local allocation peaks along the way, and doing a de-
tailed snapshot for every one would be expensive and wasteful, as all
but one of them will be later discarded. This inaccuracy can be changed
(even to 0.0%) via this option, but Massif will run drastically slower
as the number approaches zero.

--time-unit=<i|ms|B> [default: i]
The time unit used for the profiling. There are three possibilities:
instructions executed (i), which is good for most cases; real (wall-
clock) time (ms, i.e. milliseconds), which is sometimes useful; and
bytes allocated/deallocated on the heap and/or stack (B), which is use-
ful for very short-run programs, and for testing purposes, because it
is the most reproducible across different machines.

--detailed-freq=<n> [default: 10]
Frequency of detailed snapshots. With --detailed-freq=1, every snapshot
is detailed.

--max-snapshots=<n> [default: 100]
The maximum number of snapshots recorded. If set to N, for all programs
except very short-running ones, the final number of snapshots will be
between N/2 and N.

--massif-out-file=<file> [default: massif.out.%p]
Write the profile data to file rather than to the default output file,
massif.out.<pid>. The %p and %q format specifiers can be used to embed
the process ID and/or the contents of an environment variable in the
name, as is the case for the core option --log-file.

BBV OPTIONS
--bb-out-file=<name> [default: bb.out.%p]
This option selects the name of the basic block vector file. The %p and
%q format specifiers can be used to embed the process ID and/or the
contents of an environment variable in the name, as is the case for the
core option --log-file.

--pc-out-file=<name> [default: pc.out.%p]
This option selects the name of the PC file. This file holds program
counter addresses and function name info for the various basic blocks.
This can be used in conjunction with the basic block vector file to
fast-forward via function names instead of just instruction counts. The
%p and %q format specifiers can be used to embed the process ID and/or
the contents of an environment variable in the name, as is the case for
the core option --log-file.

--interval-size=<number> [default: 100000000]
This option selects the size of the interval to use. The default is 100
million instructions, which is a commonly used value. Other sizes can
be used; smaller intervals can help programs with finer-grained phases.
However smaller interval size can lead to accuracy issues due to
warm-up effects (When fast-forwarding the various architectural fea-
tures will be un-initialized, and it will take some number of instruc-
tions before they "warm up" to the state a full simulation would be at
without the fast-forwarding. Large interval sizes tend to mitigate
this.)

--instr-count-only [default: no]
This option tells the tool to only display instruction count totals,
and to not generate the actual basic block vector file. This is useful
for debugging, and for gathering instruction count info without gener-
ating the large basic block vector files.

LACKEY OPTIONS
--basic-counts=<no|yes> [default: yes]
When enabled, Lackey prints the following statistics and information
about the execution of the client program:

1. The number of calls to the function specified by the --fnname op-
tion (the default is main). If the program has had its symbols
stripped, the count will always be zero.

2. The number of conditional branches encountered and the number and
proportion of those taken.

3. The number of superblocks entered and completed by the program.
Note that due to optimisations done by the JIT, this is not at all
an accurate value.

4. The number of guest (x86, amd64, ppc, etc.) instructions and IR
statements executed. IR is Valgrind's RISC-like intermediate repre-
sentation via which all instrumentation is done.

5. Ratios between some of these counts.

6. The exit code of the client program.

--detailed-counts=<no|yes> [default: no]
When enabled, Lackey prints a table containing counts of loads, stores
and ALU operations, differentiated by their IR types. The IR types are
identified by their IR name ("I1", "I8", ... "I128", "F32", "F64", and
"V128").

--trace-mem=<no|yes> [default: no]
When enabled, Lackey prints the size and address of almost every memory
access made by the program. See the comments at the top of the file
lackey/lk_main.c for details about the output format, how it works, and
inaccuracies in the address trace. Note that this option produces im-
mense amounts of output.

--trace-superblocks=<no|yes> [default: no]
When enabled, Lackey prints out the address of every superblock (a sin-
gle entry, multiple exit, linear chunk of code) executed by the pro-
gram. This is primarily of interest to Valgrind developers. See the
comments at the top of the file lackey/lk_main.c for details about the
output format. Note that this option produces large amounts of output.

--fnname=<name> [default: main]
Changes the function for which calls are counted when --ba-
sic-counts=yes is specified.

DEBUGINFOD
Valgrind supports the downloading of debuginfo files via debuginfod, an
HTTP server for distributing ELF/DWARF debugging information. When a debug-
info file cannot be found locally, Valgrind is able to query debuginfod
servers for the file using the file's build-id.

In order to use this feature debuginfod-find must be installed and the $DE-
BUGINFOD_URLS environment variable must contain space-separated URLs of de-
buginfod servers. Valgrind does not support debuginfod-find verbose output
that is normally enabled with $DEBUGINFOD_PROGRESS and $DEBUGINFOD_VERBOSE.
These environment variables will be ignored. This feature is supported on
Linux only.

For more information regarding debuginfod, see Elfutils Debuginfod[1] .

SEE ALSO
cg_annotate(1), callgrind_annotate(1), callgrind_control(1), ms_print(1),
$INSTALL/share/doc/valgrind/html/index.html or http://www.val-
grind.org/docs/manual/index.html, Debugging your program using Valgrind's
gdbserver and GDB[2] vgdb[3], Valgrind monitor commands[4], The
Commentary[5], Scheduling and Multi-Thread Performance[6], Cachegrind: a
cache and branch-prediction profiler[7]. Execution Trees[8]

AUTHOR
See the AUTHORS file in the valgrind distribution for a comprehensive list
of authors.

This manpage was written by Andres Roldan <aroldan@debian.org> and the Val-
grind developers.

NOTES
1. Elfutils Debuginfod
https://sourceware.org/elfutils/Debuginfod.html

2. Debugging your program using Valgrind's gdbserver and GDB
http://www.valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.gdbserver

3. vgdb
http://www.valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.vgdb

4. Valgrind monitor commands
http://www.valgrind.org/docs/manual/manual-core-adv.html#manual-core-adv.valgrind-monitor-commands

5. The Commentary
http://www.valgrind.org/docs/manual/manual-core.html#manual-core.comment

6. Scheduling and Multi-Thread Performance
http://www.valgrind.org/docs/manual/manual-core.html#manual-core.pthreads_perf_sched

7. Cachegrind: a cache and branch-prediction profiler
http://www.valgrind.org/docs/manual/cg-manual.html

8. Execution Trees
http://www.valgrind.org/docs/manual/manual-core.html#manual-core.xtree

Release 3.26.0.GIT 08/01/2026 VALGRIND(1)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=valgrind&sektion=1&manpath=FreeBSD+Ports+15.1.quarterly>

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