Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
CLANG(1)			     Clang			      CLANG(1)

       clang - the Clang C, C++, and Objective-C compiler

       clang [options] filename	...

       clang  is  a C, C++, and	Objective-C compiler which encompasses prepro-
       cessing,	parsing, optimization, code generation,	assembly, and linking.
       Depending  on  which high-level mode setting is passed, Clang will stop
       before doing a full link.  While	Clang is highly	integrated, it is  im-
       portant	to  understand the stages of compilation, to understand	how to
       invoke it.  These stages	are:

       Driver The clang	executable is actually a small driver  which  controls
	      the  overall  execution of other tools such as the compiler, as-
	      sembler and linker.  Typically you do not	need to	interact  with
	      the driver, but you transparently	use it to run the other	tools.

	      This  stage handles tokenization of the input source file, macro
	      expansion, #include expansion and	handling of other preprocessor
	      directives.  The output of this stage is typically called	a ".i"
	      (for C), ".ii" (for C++),	".mi"  (for  Objective-C),  or	".mii"
	      (for Objective-C++) file.

       Parsing and Semantic Analysis
	      This  stage  parses the input file, translating preprocessor to-
	      kens into	a parse	tree.  Once in the form	of a  parse  tree,  it
	      applies  semantic	 analysis  to compute types for	expressions as
	      well and determine whether the code is well formed.  This	 stage
	      is  responsible  for generating most of the compiler warnings as
	      well as parse errors. The	output of this stage is	 an  "Abstract
	      Syntax Tree" (AST).

       Code Generation and Optimization
	      This  stage  translates  an AST into low-level intermediate code
	      (known as	"LLVM IR") and ultimately to machine code.  This phase
	      is  responsible  for  optimizing the generated code and handling
	      target-specific code generation.	The output of  this  stage  is
	      typically	called a ".s" file or "assembly" file.

	      Clang also supports the use of an	integrated assembler, in which
	      the code generator produces object files directly.  This	avoids
	      the overhead of generating the ".s" file and of calling the tar-
	      get assembler.

	      This stage runs the target assembler to translate	the output  of
	      the compiler into	a target object	file. The output of this stage
	      is typically called a ".o" file or "object" file.

       Linker This stage runs the target linker	to merge multiple object files
	      into  an executable or dynamic library. The output of this stage
	      is typically called an "a.out", ".dylib" or ".so"	file.

       Clang Static Analyzer

       The Clang Static	Analyzer is a tool that	scans source code  to  try  to
       find  bugs  through  code analysis.  This tool uses many	parts of Clang
       and   is	  built	  into	 the   same    driver.	   Please    see    <->	 for  more  details  on	how to use the
       static analyzer.

   Stage Selection Options
       -E     Run the preprocessor stage.

	      Run the preprocessor, parser and type checking stages.

       -S     Run the previous stages as well as LLVM generation and optimiza-
	      tion  stages  and	 target-specific code generation, producing an
	      assembly file.

       -c     Run all of the above, plus the assembler,	 generating  a	target
	      ".o" object file.

       no stage	selection option
	      If  no stage selection option is specified, all stages above are
	      run, and the linker is run to combine the	results	into  an  exe-
	      cutable or shared	library.

   Language Selection and Mode Options
       -x <language>
	      Treat subsequent input files as having type language.

	      Specify the language standard to compile for.

	      Supported	values for the C language are:

		     ISO C 1990

		     ISO C 1990	with amendment 1

		     ISO C 1990	with GNU extensions

		     ISO C 1999

		     ISO C 1999	with GNU extensions

		     ISO C 2011

		     ISO C 2011	with GNU extensions

		     ISO C 2017

		     ISO C 2017	with GNU extensions

	      The  default  C language standard	is gnu11, except on PS4, where
	      it is gnu99.

	      Supported	values for the C++ language are:

		     ISO C++ 1998 with amendments

		     ISO C++ 1998 with amendments and GNU extensions

		     ISO C++ 2011 with amendments

		     ISO C++ 2011 with amendments and GNU extensions

		     ISO C++ 2014 with amendments

		     ISO C++ 2014 with amendments and GNU extensions

		     ISO C++ 2017 with amendments

		     ISO C++ 2017 with amendments and GNU extensions

		     Working draft for ISO C++ 2020

		     Working draft for ISO C++ 2020 with GNU extensions

	      The default C++ language standard	is gnu++14.

	      Supported	values for the OpenCL language are:

		     OpenCL 1.0

		     OpenCL 1.1

		     OpenCL 1.2

		     OpenCL 2.0

	      The default OpenCL language standard is cl1.0.

	      Supported	values for the CUDA language are:

		     NVIDIA CUDA(tm)

	      Specify the C++ standard library to use; supported  options  are
	      libstdc++	and libc++. If not specified, platform default will be

	      Specify the compiler runtime library to use;  supported  options
	      are  libgcc  and compiler-rt. If not specified, platform default
	      will be used.

       -ansi  Same as -std=c89.

       -ObjC, -ObjC++
	      Treat source input files as Objective-C  and  Object-C++	inputs

	      Enable trigraphs.

	      Indicate	that  the  file	should be compiled for a freestanding,
	      not a hosted, environment.

	      Disable special handling and optimizations of builtin  functions
	      like strlen() and	malloc().

	      Indicate	that  math functions should be treated as updating er-

	      Enable support for Pascal-style strings with "\pfoo".

	      Enable support for Microsoft extensions.

	      Set _MSC_VER. Defaults to	1300 on	Windows. Not set otherwise.

	      Enable support for Borland extensions.

	      Make all string literals default	to  writable.	This  disables
	      uniquing of strings and other optimizations.

       -flax-vector-conversions,	      -flax-vector-conversions=<kind>,
	      Allow loose type checking	rules for implicit vector conversions.
	      Possible values of <kind>:

	      o	none: allow no implicit	conversions between vectors

	      o	integer:  allow	 implicit  bitcasts between integer vectors of
		the same overall bit-width

	      o	all: allow implicit bitcasts between any vectors of  the  same
		overall	bit-width

	      <kind> defaults to integer if unspecified.

	      Enable the "Blocks" language feature.

	      Select  the  Objective-C	ABI version to use. Available versions
	      are 1 (legacy "fragile" ABI),  2	(non-fragile  ABI  1),	and  3
	      (non-fragile ABI 2).

	      Select  the  Objective-C	non-fragile  ABI version to use	by de-
	      fault. This will only be used as the Objective-C	ABI  when  the
	      non-fragile ABI is enabled (either via -fobjc-nonfragile-abi, or
	      because it is the	platform default).

       -fobjc-nonfragile-abi, -fno-objc-nonfragile-abi
	      Enable use of the	Objective-C non-fragile	ABI. On	platforms  for
	      which  this  is  the  default  ABI,  it  can  be	disabled  with

   Target Selection Options
       Clang fully supports cross compilation as an inherent part of  its  de-
       sign.   Depending  on  how  your	version	of Clang is configured,	it may
       have support for	a number of cross compilers, or	may only support a na-
       tive target.

       -arch <architecture>
	      Specify the architecture to build	for.

	      When  building  for macOS, specify the minimum version supported
	      by your application.

	      When building for	iPhone OS, specify the	minimum	 version  sup-
	      ported by	your application.

	      Print  out  a  list of supported processors for the given	target
	      (specified through --target=<architecture> or  -arch  <architec-
	      ture>).  If  no  target  is specified, the system	default	target
	      will be used.

       -mcpu=?,	-mtune=?
	      Aliases of --print-supported-cpus

	      Specify that Clang should	generate code for a specific processor
	      family   member	and   later.   For  example,  if  you  specify
	      -march=i486, the compiler	is allowed  to	generate  instructions
	      that  are	 valid on i486 and later processors, but which may not
	      exist on earlier ones.

   Code	Generation Options
       -O0, -O1, -O2, -O3, -Ofast, -Os,	-Oz, -Og, -O, -O4
	      Specify which optimization level to use:
		 -O0 Means "no optimization": this level compiles the  fastest
		 and generates the most	debuggable code.

		 -O1 Somewhere between -O0 and -O2.

		 -O2  Moderate	level of optimization which enables most opti-

		 -O3 Like -O2, except that it enables optimizations that  take
		 longer	to perform or that may generate	larger code (in	an at-
		 tempt to make the program run faster).

		 -Ofast	Enables	all the	 optimizations	from  -O3  along  with
		 other	aggressive  optimizations that may violate strict com-
		 pliance with language standards.

		 -Os Like -O2 with extra optimizations to reduce code size.

		 -Oz Like -Os (and thus	-O2), but reduces code size further.

		 -Og Like -O1. In future versions, this	option	might  disable
		 different optimizations in order to improve debuggability.

		 -O Equivalent to -O2.

		 -O4 and higher
		     Currently equivalent to -O3

       -g, -gline-tables-only, -gmodules
	      Control  debug information output.  Note that Clang debug	infor-
	      mation works best	at -O0.	 When more than	 one  option  starting
	      with -g is specified, the	last one wins:
		 -g Generate debug information.

		 -gline-tables-only  Generate  only  line table	debug informa-
		 tion. This allows for symbolicated backtraces	with  inlining
		 information, but does not include any information about vari-
		 ables,	their locations	or types.

		 -gmodules Generate debug information that  contains  external
		 references  to	 types defined in Clang	modules	or precompiled
		 headers instead of emitting redundant debug type  information
		 into  every  object file.  This option	transparently switches
		 the Clang module format to object file	containers  that  hold
		 the  Clang  module together with the debug information.  When
		 compiling a program that uses Clang  modules  or  precompiled
		 headers, this option produces complete	debug information with
		 faster	compile	times and much smaller object files.

		 This option should not	be used	when building static libraries
		 for  distribution  to	other  machines	because	the debug info
		 will contain references to the	module cache  on  the  machine
		 the object files in the library were built on.

       -fstandalone-debug -fno-standalone-debug
	      Clang  supports  a number	of optimizations to reduce the size of
	      debug information	in the binary. They work based on the  assump-
	      tion that	the debug type information can be spread out over mul-
	      tiple compilation	units.	For instance, Clang will not emit type
	      definitions  for types that are not needed by a module and could
	      be replaced with a forward  declaration.	 Further,  Clang  will
	      only  emit  type info for	a dynamic C++ class in the module that
	      contains the vtable for the class.

	      The -fstandalone-debug option  turns  off	 these	optimizations.
	      This  is useful when working with	3rd-party libraries that don't
	      come with	debug information.  This is  the  default  on  Darwin.
	      Note  that Clang will never emit type information	for types that
	      are not referenced at all	by the program.

	      Enable generation	of unwind information. This allows  exceptions
	      to be thrown through Clang compiled stack	frames.	 This is on by
	      default in x86-64.

	      Generate code to catch integer overflow errors.  Signed  integer
	      overflow is undefined in C. With this flag, extra	code is	gener-
	      ated to detect this and abort when it happens.

	      This flag	sets the default visibility level.

       -fcommon, -fno-common
	      This flag	specifies that variables without initializers get com-
	      mon linkage.  It can be disabled with -fno-common.

	      Set  the	default	 thread-local  storage	(TLS) model to use for
	      thread-local variables. Valid values are:	"global-dynamic", "lo-
	      cal-dynamic",  "initial-exec"  and  "local-exec".	The default is
	      "global-dynamic".	The default model can be overridden  with  the
	      tls_model	 attribute. The	compiler will try to choose a more ef-
	      ficient model if possible.

       -flto, -flto=full, -flto=thin, -emit-llvm
	      Generate output files in LLVM formats, suitable  for  link  time
	      optimization.   When used	with -S	this generates LLVM intermedi-
	      ate language assembly files, otherwise this generates LLVM  bit-
	      code  format object files	(which may be passed to	the linker de-
	      pending on the stage selection options).

	      The default for -flto is "full", in which	the  LLVM  bitcode  is
	      suitable	for monolithic Link Time Optimization (LTO), where the
	      linker merges all	such modules into a single combined module for
	      optimization.  With  "thin",  ThinLTO compilation	is invoked in-

   Driver Options
       -###   Print (but do not	run) the commands to run for this compilation.

       --help Display available	options.

	      Do not emit any warnings for unused driver arguments.

	      Pass the comma separated arguments in args to the	assembler.

	      Pass the comma separated arguments in args to the	linker.

	      Pass the comma separated arguments in args to the	preprocessor.

       -Xanalyzer <arg>
	      Pass arg to the static analyzer.

       -Xassembler <arg>
	      Pass arg to the assembler.

       -Xlinker	<arg>
	      Pass arg to the linker.

       -Xpreprocessor <arg>
	      Pass arg to the preprocessor.

       -o <file>
	      Write output to file.

	      Print the	full library path of file.

	      Print the	library	path for the currently used  compiler  runtime
	      library ("libgcc.a" or "libclang_rt.builtins.*.a").

	      Print the	full program path of name.

	      Print the	paths used for finding libraries and programs.

	      Save intermediate	compilation results.

       -save-stats, -save-stats=cwd, -save-stats=obj
	      Save internal code generation (LLVM) statistics to a file	in the
	      current directory	(-save-stats/"-save-stats=cwd")	or the	direc-
	      tory of the output file ("-save-state=obj").

       -integrated-as, -no-integrated-as
	      Used  to	enable and disable, respectively, the use of the inte-
	      grated assembler.	Whether	the integrated assembler is on by  de-
	      fault is target dependent.

       -time  Time individual commands.

	      Print timing summary of each stage of compilation.

       -v     Show commands to run and use verbose output.

   Diagnostics Options
       -fshow-column,  -fshow-source-location, -fcaret-diagnostics, -fdiagnos-
       tics-fixit-info,	      -fdiagnostics-parseable-fixits,	    -fdiagnos-
       tics-print-source-range-info,   -fprint-source-range-info,   -fdiagnos-
       tics-show-option, -fmessage-length
	      These options control how	Clang prints out information about di-
	      agnostics	 (errors  and  warnings).  Please see the Clang	User's
	      Manual for more information.

   Preprocessor	Options
	      Adds an implicit #define into the	 predefines  buffer  which  is
	      read before the source file is preprocessed.

	      Adds an implicit #undef into the predefines buffer which is read
	      before the source	file is	preprocessed.

       -include	<filename>
	      Adds an implicit #include	into the predefines  buffer  which  is
	      read before the source file is preprocessed.

	      Add  the	specified  directory  to  the  search path for include

	      Add the specified	directory to the search	path for framework in-
	      clude files.

	      Do  not  search  the  standard  system  directories  or compiler
	      builtin directories for include files.

	      Do not search the	standard system	directories for	include	files,
	      but do search compiler builtin include directories.

	      Do not search clang's builtin directory for include files.

	      These environment	variables are checked, in order, for the loca-
	      tion to  write  temporary	 files	used  during  the  compilation

       CPATH  If  this environment variable is present,	it is treated as a de-
	      limited list of paths to be added	to the default system  include
	      path list. The delimiter is the platform dependent delimiter, as
	      used in the PATH environment variable.

	      Empty components in the environment variable are ignored.

	      These  environment  variables  specify  additional paths,	as for
	      CPATH, which are only used when processing the appropriate  lan-

	      If  -mmacosx-version-min	is unspecified,	the default deployment
	      target is	read from this environment variable. This option  only
	      affects Darwin targets.

       To  report  bugs,  please visit <>.  Most bug re-
       ports should include preprocessed source	files (use the -E option)  and
       the full	output of the compiler,	along with information to reproduce.

       as(1), ld(1)

       Maintained by the Clang / LLVM Team (<>)

       2007-2020, The Clang Team

10				  2020-06-26			      CLANG(1)


Want to link to this manual page? Use this URL:

home | help