pahole(1) dwarves pahole(1) NAME pahole - Shows, manipulates data structure layout and pretty prints raw data. SYNOPSIS pahole [options] files DESCRIPTION pahole shows data structure layouts encoded in debugging information for- mats, DWARF, CTF and BTF being supported. This is useful for, among other things: optimizing important data struc- tures by reducing its size, figuring out what is the field sitting at an offset from the start of a data structure, investigating ABI changes and more generally understanding a new codebase you have to work with. It also uses these structure layouts to pretty print data feed to its stan- dard input, e.g.: $ pahole --header elf64_hdr --prettify /lib/modules/5.8.0-rc6+/build/vmlinux { .e_ident = { 127, 69, 76, 70, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0 }, .e_type = 2, .e_machine = 62, .e_version = 1, .e_entry = 16777216, .e_phoff = 64, .e_shoff = 604653784, .e_flags = 0, .e_ehsize = 64, .e_phentsize = 56, .e_phnum = 5, .e_shentsize = 64, .e_shnum = 80, .e_shstrndx = 79, }, $ See the PRETTY PRINTING section for further examples and documentation. The files must have associated debugging information. This information may be inside the file itself, in ELF sections, or in another file. One way to have this information is to specify the -g option to the com- piler when building it. When this is done the information will be stored in an ELF section. For the DWARF debugging information format this, adds, among others, the .debug_info ELF section. For CTF it is found in just one ELF section, .SUNW_ctf. BTF comes in at least the .BTF ELF section, and may come also with the .BTF.ext ELF section. The debuginfo packages available in most Linux distributions are also sup- ported by pahole, where the debugging information is available in a sepa- rate file. By default, pahole shows the layout of all named structs in the files spec- ified. If no files are specified, then it will look if the /sys/kernel/btf/vmlinux is present, using the BTF information present in it about the running ker- nel, i.e. this works: $ pahole list_head struct list_head { struct list_head * next; /* 0 8 */ struct list_head * prev; /* 8 8 */ /* size: 16, cachelines: 1, members: 2 */ /* last cacheline: 16 bytes */ }; $ It is possible to override the /sys/kernel/btf/vmlinux file location by setting the PAHOLE_VMLINUX_BTF_FILENAME environment variable. This may be useful for testing, scripting when using a different BTF for vmlinux. Used in the pahole regression tests. If BTF is not present and no file is passed, then a vmlinux that matches the build-id for the running kernel will be looked up in the usual places, including where the kernel debuginfo packages put it, looking for DWARF info instead. See the EXAMPLES section for more usage suggestions. It also pretty prints whatever is fed to its standard input, according to the type specified, see the EXAMPLE session. Use --count to state how many records should be pretty printed. OPTIONS pahole supports the following options. -C, --class_name=CLASS_NAMES Show just these classes. This can be a comma separated list of class names or file URLs (e.g.: file://class_list.txt) -c, --cacheline_size=SIZE Set cacheline size to SIZE bytes. --sort Sort the output by type name, maybe this will grow to allow sorting by other criteria. This is mostly needed so that pretty printing from BTF and DWARF can be comparable when using using multiple threads to load DWARF data, when the order that the types in the compile units is processed is not deterministic. --compile Generate compileable code, with all definitions for all types, i.e.: $ pahole --compile > vmlinux.h Produces a header that can be included in a C source file and built. In the example provided it will use the BTF info if available, otherwise will look for a DWARF file matching the running kernel build-id. --skip_emitting_atomic_typedefs Do not emit 'typedef _Atomic int atomic_int' & friends when used with options like --compile. Use it if the compiler provides these already, as of circa 2022 with gcc 12.2.1 those are not encoded in DWARF so to generate compilable code we need emit those typedefs for the atomic types used in the data structures being emitted from de- bugging information. --count=COUNT Pretty print the first COUNT records from input. --skip=COUNT Skip COUNT input records. -E, --expand_types Expand class members. Useful to find in what member of inner structs where an offset from the beginning of a struct is. -F, --format_path Allows specifying a list of debugging formats to try, in order. Right now this includes "btf", "ctf" and "dwarf". The default format path used is equivalent to "-F dwarf,btf,ctf". --hashbits=BITS Allows specifying the number of bits for the debugging format loader to use. The only one affected so far is the "dwarf" one, its de- fault now is 15, the maximum for it is now 21 bits. Tweak it to see if it improves performance as the kernel evolves and more types and functions have to be loaded. --hex Print offsets and sizes in hexadecimal. -r, --rel_offset Show relative offsets of members in inner structs. -p, --expand_pointers Expand class pointer members. -R, --reorganize Reorganize struct, demoting and combining bitfields, moving members to remove alignment holes and padding. -S, --show_reorg_steps Show the struct layout at each reorganization step. -i, --contains=CLASS_NAME Show classes that contains CLASS_NAME. --contains_enumerator=ENUMERATOR_NAME Show enumeration that contains ENUMERATOR_NAME. $ pahole --contains_enumerator S_VERSION enum file_time_flags { S_ATIME = 1, S_MTIME = 2, S_CTIME = 4, S_VERSION = 8, } $ -a, --anon_include Include anonymous classes. -A, --nested_anon_include Include nested (inside other structs) anonymous classes. -B, --bit_holes=NR_HOLES Show only structs at least NR_HOLES bit holes. -d, --recursive Recursive mode, affects several other flags. -D, --decl_exclude=PREFIX exclude classes declared in files with PREFIX. -f, --find_pointers_to=CLASS_NAME Find pointers to CLASS_NAME. -H, --holes=NR_HOLES Show only structs with at least NR_HOLES holes. --padding=SIZE_PADDING Show only structs with SIZE_PADDING bytes of padding at its end. --padding_ge=SIZE_PADDING Show only structs with at least SIZE_PADDING bytes of padding at its end. -I, --show_decl_info Show the file and line number where the tags were defined, if avail- able in the debugging information. --skip_encoding_btf_vars By default, VARs are encoded only for percpu variables. When speci- fied, this option prevents encoding any VARs. Note that this option can be overridden by the feature "global_var". --skip_encoding_btf_decl_tag Do not encode decl tags in BTF. --skip_encoding_btf_enum64 Do not encode enum64 in BTF. --skip_encoding_btf_type_tag Do not encode type tags in BTF. --skip_encoding_btf_inconsistent_proto Do not encode functions with multiple inconsistent prototypes or un- expected register use for their parameters, where the registers used do not match calling conventions. -j, --jobs=N Run N jobs in parallel. Defaults to number of online processors + 10% (like the 'ninja' build system) if no argument is specified. -J, --btf_encode Encode BTF information from DWARF, used in the Linux kernel build process when CONFIG_DEBUG_INFO_BTF=y is present, introduced in Linux v5.2. Used to implement features such as BPF CO-RE (Compile Once - Run Everywhere). See https://nakryiko.com/posts/bpf-portability-and-co-re/. --btf_encode_detached=FILENAME Same thing as -J/--btf_encode, but storing the raw BTF info into a separate file. --btf_encode_force Ignore those symbols found invalid when encoding BTF. --btf_base=PATH Path to the base BTF file, for instance: vmlinux when encoding ker- nel module BTF information. This may be inferred when asking for a /sys/kernel/btf/MODULE, when it will be autoconfigured to "/sys/ker- nel/btf/vmlinux". --btf_gen_floats Allow producing BTF_KIND_FLOAT entries in systems where the vmlinux DWARF information has float types. --btf_gen_optimized Generate BTF for functions with optimization-related suffixes (.isra, .constprop). --btf_gen_all Allow using all the BTF features supported by pahole. --btf_features=FEATURE_LIST Encode BTF using the specified feature list, or specify 'default' for all standard features supported. This option can be used as an alternative to using multiple BTF-related options, and 'default' represents the standard set of BTF features that are in use for ker- nel BTF generation, so is useful as a shortcut for testing the lat- est set of standard features. However kernel builds will call out specific features rather than using 'default' to ensure that the de- sired features are enabled regardless of pahole version and associ- ated 'default' set. Supported standard features are encode_force Ignore invalid symbols when encoding BTF; for example if a symbol has an invalid name, it will be ignored and BTF encoding will continue. var Encode percpu variables using BTF_KIND_VAR in BTF. float Encode floating-point types in BTF. decl_tag Encode declaration tags using BTF_KIND_DECL_TAG. type_tag Encode type tags using BTF_KIND_TYPE_TAG. enum64 Encode enum64 values with BTF_KIND_ENUM64. optimized_func Encode representations of optimized functions with suffixes like ".isra.0". consistent_func Avoid encoding inconsistent static functions. These occur when a parameter is optimized out in some CUs and not others, or when the same function name has inconsistent BTF descriptions in different CUs. Supported non-standard features (not enabled for 'default') attributes Allow generation of decl_tags and type_tags with kind_flag = 1. These tags can be used to encode arbitrary compiler attributes in BTF, but are backward incompatible. decl_tag_kfuncs Inject a BTF_KIND_DECL_TAG for each discovered kfunc. distilled_base For split BTF, generate a distilled version of the associated base BTF to support later relocation of split BTF with a possibly changed base, storing it in a .BTF.base ELF section. global_var Encode all global variables using BTF_KIND_VAR in BTF. So for example, specifying --btf_encode=var,enum64 will result in a BTF encoding that (as well as encoding basic BTF information) will contain variables and enum64 values. If one wants to add an extra feature to the set of standard ones, the '+' prefix can be used, i.e.: --btf_features=+reproducible_build will add all default features plus the 'reproducible_build' extra feature. --btf_features_strict Identical to --btf_features above, but pahole will exit if it en- counters an unrecognized feature. --supported_btf_features Show set of BTF features supported by --btf_features option and exit. Useful for checking which features are supported since --btf_features will not emit an error if an unrecognized feature is specified. --running_kernel_vmlinux, Search for, possibly getting from a debuginfo server, a vmlinux matching the running kernel build-id (from /sys/kernel/notes). -l, --show_first_biggest_size_base_type_member Show first biggest size base_type member. -m, --nr_methods Show number of methods of all classes, i.e. the number of functions have arguments that are pointers to a given class. To get the number of methods for an specific class, please use: $ pahole --nr_methods | grep -w sock sock 1005 $ In the above example it used the BTF information in /sys/ker- nel/btf/vmlinux. -M, --show_only_data_members Show only the members that use space in the class layout. C++ meth- ods will be suppressed. -n, --nr_members Show number of members. -N, --class_name_len Show size of classes. -O, --dwarf_offset=OFFSET Show tag with DWARF OFFSET. -P, --packable Show only structs that has holes that can be packed if members are reorganized, for instance when using the --reorganize option. -P, --with_flexible_array Show only structs that have a flexible array. -P, --with_embedded_flexible_array Show only structs that have an embedded flexible array, i.e. a con- tained struct that has flexible arrays, a flexible array "in the middle". -q, --quiet Be quieter. -s, --sizes Show size of classes. -t, --separator=SEP Use SEP as the field separator. -T, --nr_definitions Show how many times struct was defined. -u, --defined_in Show CUs where CLASS_NAME (-C) is defined. --flat_arrays Flatten arrays, so that array[10][2] becomes array[20]. Useful when generating from both CTF/BTF and DWARF encodings for the same binary for testing purposes. --suppress_aligned_attribute Suppress forced alignment markers, so that one can compare BTF or CTF output, that don't have that info, to output from DWARF >= 5. --suppress_force_paddings Suppress bitfield forced padding at the end of structs, as this re- quires something like DWARF's DW_AT_alignment, so that one can com- pare BTF or CTF output, that don't have that info. --suppress_packed Suppress the output of the inference of __attribute__((__packed__)), so that one can compare BTF or CTF output, the inference algorithm uses things like DW_AT_alignment, so until it is improved to infer that as well for BTF, allow disabling this output. --fixup_silly_bitfields Converts silly bitfields such as "int foo:32" to plain "int foo". -V, --verbose be verbose --ptr_table_stats Print statistics about ptr_table data structures, used to hold all the types, tags and functions data structures, for development tun- ing of such tables, tuned for a typical 2021 vmlinux file. -w, --word_size=WORD_SIZE Change the arch word size to WORD_SIZE. -x, --exclude=PREFIX Exclude PREFIXed classes. -X, --cu_exclude=PREFIX Exclude PREFIXed compilation units. --lang=languages Only process compilation units built from source code written in the specified languages. Supported languages: ada83, ada95, asm, bliss, c, c89, c99, c11, c++, c++03, c++11, c++14, cobol74, cobol85, d, dylan, fortran77, fortran90, fortran95, fortran03, fortran08, go, haskell, java, julia, modula2, modula3, objc, objc++, ocaml, opencl, pascal83, pli, python, renderscript, rust, swift, upc The linux kernel, for instance, is written in 'c89' circa 2022, use that in filters. --lang_exclude=languages Don't process compilation units built from source code written in the specified languages. To filter out compilation units written in Rust, for instance, use: pahole -j --btf_encode --lang_exclude rust This can also be accomplished by setting the environment variable PAHOLE_LANG_EXCLUDE to the same list of languages, for instance, the following is equivalent to the above: export PAHOLE_LANG_EXCLUDE=rust pahole -j --btf_encode Meaning in both cases 'rust' CUs will be skipped. This is useful for scripts where it provides a way to ask for that exclusion for pahole and pfunct, no need to use --lang_exclude in all calls to those tools, just set that environment variable. -y, --prefix_filter=PREFIX Include PREFIXed classes. -z, --hole_size_ge=HOLE_SIZE Show only structs with at least one hole greater or equal to HOLE_SIZE. --structs Show only structs, all the other filters apply, i.e. to show just the sizes of all structs combine --structs with --sizes, etc. --packed Show only packed structs, all the other filters apply, i.e. to show just the sizes of all packed structs combine --packed with --sizes, etc. --unions Show only unions, all the other filters apply, i.e. to show just the sizes of all unions combine --union with --sizes, etc. --version Show a traditional string version, i.e.: "v1.18". --numeric_version Show a numeric only version, suitable for use in Makefiles and scripts where one wants to know what if the installed version has some feature, i.e.: 118 instead of "v1.18". --kabi_prefix=STRING When the prefix of the string is STRING, treat the string as STRING. NOTES To enable the generation of debugging information in the Linux kernel build process select CONFIG_DEBUG_INFO. This can be done using make menuconfig by this path: "Kernel Hacking" -> "Compile-time checks and compiler options" -> "Compile the kernel with debug info". Consider as well enabling CON- FIG_DEBUG_INFO_BTF by going thru the aforementioned menuconfig path and then selecting "Generate BTF typeinfo". Most modern distributions with eBPF support should come with that in all its kernels, greatly facilitating the use of pahole. Many distributions also come with debuginfo packages, so just enable it in your package manager repository configuration and install the kernel-debug- info, or any other userspace program written in a language that the com- piler generates debuginfo (C, C++, for instance). EXAMPLES All the examples here use either /sys/kernel/btf/vmlinux, if present, or lookup a vmlinux file matching the running kernel, using the build-id info found in /sys/kernel/notes to make sure it matches. Show a type: $ pahole -C __u64 typedef long long unsigned int __u64; $ Works as well if the only argument is a type name: $ pahole raw_spinlock_t typedef struct raw_spinlock raw_spinlock_t; $ Multiple types can be passed, separated by commas: $ pahole raw_spinlock_t,raw_spinlock struct raw_spinlock { arch_spinlock_t raw_lock; /* 0 4 */ /* size: 4, cachelines: 1, members: 1 */ /* last cacheline: 4 bytes */ }; typedef struct raw_spinlock raw_spinlock_t; $ Types can be expanded: $ pahole -E raw_spinlock struct raw_spinlock { /* typedef arch_spinlock_t */ struct qspinlock { union { /* typedef atomic_t */ struct { int counter; /* 0 4 */ } val; /* 0 4 */ struct { /* typedef u8 -> __u8 */ unsigned char locked; /* 0 1 */ /* typedef u8 -> __u8 */ unsigned char pending; /* 1 1 */ }; /* 0 2 */ struct { /* typedef u16 -> __u16 */ short unsigned int locked_pending; /* 0 2 */ /* typedef u16 -> __u16 */ short unsigned int tail; /* 2 2 */ }; /* 0 4 */ }; /* 0 4 */ } raw_lock; /* 0 4 */ /* size: 4, cachelines: 1, members: 1 */ /* last cacheline: 4 bytes */ }; $ When decoding OOPSes you may want to see the offsets and sizes in hexadeci- mal: $ pahole --hex thread_struct struct thread_struct { struct desc_struct tls_array[3]; /* 0 0x18 */ long unsigned int sp; /* 0x18 0x8 */ short unsigned int es; /* 0x20 0x2 */ short unsigned int ds; /* 0x22 0x2 */ short unsigned int fsindex; /* 0x24 0x2 */ short unsigned int gsindex; /* 0x26 0x2 */ long unsigned int fsbase; /* 0x28 0x8 */ long unsigned int gsbase; /* 0x30 0x8 */ struct perf_event * ptrace_bps[4]; /* 0x38 0x20 */ /* --- cacheline 1 boundary (64 bytes) was 24 bytes ago --- */ long unsigned int debugreg6; /* 0x58 0x8 */ long unsigned int ptrace_dr7; /* 0x60 0x8 */ long unsigned int cr2; /* 0x68 0x8 */ long unsigned int trap_nr; /* 0x70 0x8 */ long unsigned int error_code; /* 0x78 0x8 */ /* --- cacheline 2 boundary (128 bytes) --- */ struct io_bitmap * io_bitmap; /* 0x80 0x8 */ long unsigned int iopl_emul; /* 0x88 0x8 */ mm_segment_t addr_limit; /* 0x90 0x8 */ unsigned int sig_on_uaccess_err:1; /* 0x98: 0 0x4 */ unsigned int uaccess_err:1; /* 0x98:0x1 0x4 */ /* XXX 30 bits hole, try to pack */ /* XXX 36 bytes hole, try to pack */ /* --- cacheline 3 boundary (192 bytes) --- */ struct fpu fpu; /* 0xc0 0x1040 */ /* size: 4352, cachelines: 68, members: 20 */ /* sum members: 4312, holes: 1, sum holes: 36 */ /* sum bitfield members: 2 bits, bit holes: 1, sum bit holes: 30 bits */ }; $ OK, I know the offset that causes its a 'struct thread_struct' and that the offset is 0x178, so must be in that 'fpu' struct... No problem, expand 'struct thread_struct' and combine with grep: $ pahole --hex -E thread_struct | egrep '(0x178|struct fpu)' -B4 -A4 /* XXX 30 bits hole, try to pack */ /* XXX 36 bytes hole, try to pack */ /* --- cacheline 3 boundary (192 bytes) --- */ struct fpu { unsigned int last_cpu; /* 0xc0 0x4 */ /* XXX 4 bytes hole, try to pack */ -- /* typedef u8 -> __u8 */ unsigned char alimit; /* 0x171 0x1 */ /* XXX 6 bytes hole, try to pack */ struct math_emu_info * info; /* 0x178 0x8 */ /* --- cacheline 6 boundary (384 bytes) --- */ /* typedef u32 -> __u32 */ unsigned int entry_eip; /* 0x180 0x4 */ } soft; /* 0x100 0x88 */ struct xregs_state { $ Want to know where 'struct thread_struct' is defined in the kernel sources? $ pahole -I thread_struct | head -2 /* Used at: /sys/kernel/btf/vmlinux */ /* <0> (null):0 */ $ Not present in BTF, so use DWARF, takes a little bit longer, and assuming it finds the matching vmlinux file: $ pahole -Fdwarf -I thread_struct | head -2 /* Used at: /home/acme/git/linux/arch/x86/kernel/head64.c */ /* <3333> /home/acme/git/linux/arch/x86/include/asm/processor.h:485 */ $ To find the biggest data structures in the Linux kernel: $ pahole -s | sort -k2 -nr | head -5 cmp_data 290904 1 dec_datas 274520 1 cpu_entry_area 217088 0 pglist_data 172928 4 saved_cmdlines_buffer 131104 1 $ The second column is the size in bytes and the third is the number of alignment holes in that structure. Show data structures that have a raw spinlock and are related to the RCU mechanism: $ pahole --contains raw_spinlock_t --prefix rcu rcu_node rcu_data rcu_state $ To see that in context, combine it with grep: $ pahole rcu_state | grep raw_spinlock_t -B1 -A5 /* --- cacheline 52 boundary (3328 bytes) --- */ raw_spinlock_t ofl_lock; /* 3328 4 */ /* size: 3392, cachelines: 53, members: 35 */ /* sum members: 3250, holes: 7, sum holes: 82 */ /* padding: 60 */ }; $ PRETTY PRINTING pahole can also use the data structure types to pretty print raw data spec- ified via --prettify. To consume raw data from the standard input, just use '--prettify -' It can also pretty print raw data from stdin according to the type speci- fied: $ pahole -C modversion_info drivers/scsi/sg.ko struct modversion_info { long unsigned int crc; /* 0 8 */ char name[56]; /* 8 56 */ /* size: 64, cachelines: 1, members: 2 */ }; $ $ objcopy -O binary --only-section=__versions drivers/scsi/sg.ko versions $ $ ls -la versions -rw-rw-r--. 1 acme acme 7616 Jun 25 11:33 versions $ $ pahole --count 3 -C modversion_info drivers/scsi/sg.ko --prettify versions { .crc = 0x8dabd84, .name = "module_layout", }, { .crc = 0x45e4617b, .name = "no_llseek", }, { .crc = 0xa23fae8c, .name = "param_ops_int", }, $ $ pahole --skip 1 --count 2 -C modversion_info drivers/scsi/sg.ko --prettify - < versions { .crc = 0x45e4617b, .name = "no_llseek", }, { .crc = 0xa23fae8c, .name = "param_ops_int", }, $ This is equivalent to: $ pahole --seek_bytes 64 --count 1 -C modversion_info drivers/scsi/sg.ko --prettify versions { .crc = 0x45e4617b, .name = "no_llseek", }, $ -C, --class_name=CLASS_NAME Pretty print according to this class. Arguments may be passed to it to affect how the pretty printing is performed, e.g.: -C 'perf_event_header(sizeof,type,type_enum=perf_event_type,filter=type==PERF_RECORD_EXIT)' This would select the 'struct perf_event_header' as the type to use to pretty print records states that the 'size' field in that struct should be used to figure out the size of the record (variable sized records), that the 'enum perf_event_type' should be used to pretty print the numeric value in perf_event_header->type and furthermore that it should be used to heuristically look for structs with the same name (lowercase) of the enum entry that is converted from the type field, using it to pretty print in- stead of the base 'perf_event_header' type. See the PRETTY PRINTING EXAM- PLES section below. Furthermore the 'filter=' part can be used, so far with only the '==' oper- ator to filter based on the 'type' field and converting the string 'PERF_RECORD_EXIT' to a number according to type_enum. The 'sizeof' arg defaults to the 'size' member name, if the name is differ- ent, one can use 'sizeof=sz' form, ditto for 'type=other_member_name' field, that defaults to 'type'. PRETTY PRINTING EXAMPLES Looking at the ELF header for a vmlinux file, using BTF, first lets dis- cover the ELF header type: $ pahole --sizes | grep -i elf | grep -i _h elf64_hdr 64 0 elf32_hdr 52 0 $ Now we can use this to show the first record from offset zero: $ pahole -C elf64_hdr --count 1 --prettify /lib/modules/5.8.0-rc3+/build/vmlinux { .e_ident = { 127, 69, 76, 70, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0 }, .e_type = 2, .e_machine = 62, .e_version = 1, .e_entry = 16777216, .e_phoff = 64, .e_shoff = 775923840, .e_flags = 0, .e_ehsize = 64, .e_phentsize = 56, .e_phnum = 5, .e_shentsize = 64, .e_shnum = 80, .e_shstrndx = 79, }, $ This is equivalent to: $ pahole --header elf64_hdr --prettify /lib/modules/5.8.0-rc3+/build/vmlinux The --header option also allows reference in other command line options to fields in the header. This is useful when one wants to show multiple records in a file and the range where those fields are located is specified in header fields, such as for perf.data files: $ pahole --hex ~/bin/perf --header perf_file_header --prettify perf.data { .magic = 0x32454c4946524550, .size = 0x68, .attr_size = 0x88, .attrs = { .offset = 0xa8, .size = 0x88, }, .data = { .offset = 0x130, .size = 0x588, }, .event_types = { .offset = 0, .size = 0, }, .adds_features = { 0x16717ffc, 0, 0, 0 }, }, $ So to display the cgroups records in the perf_file_header.data section we can use: $ pahole ~/bin/perf --header=perf_file_header --seek_bytes '$header.data.offset' --size_bytes='$header.data.size' -C 'perf_event_header(sizeof,type,type_enum=perf_event_type,filter=type==PERF_RECORD_CGROUP)' --prettify perf.data { .header = { .type = PERF_RECORD_CGROUP, .misc = 0, .size = 40, }, .id = 1, .path = "/", }, { .header = { .type = PERF_RECORD_CGROUP, .misc = 0, .size = 48, }, .id = 1553, .path = "/system.slice", }, { .header = { .type = PERF_RECORD_CGROUP, .misc = 0, .size = 48, }, .id = 8, .path = "/machine.slice", }, { .header = { .type = PERF_RECORD_CGROUP, .misc = 0, .size = 128, }, .id = 7828, .path = "/machine.slice/libpod-42be8e8d4eb9d22405845005f0d04ea398548dccc934a150fbaa3c1f1f9492c2.scope", }, { .header = { .type = PERF_RECORD_CGROUP, .misc = 0, .size = 88, }, .id = 13, .path = "/machine.slice/machine-qemu\x2d1\x2drhel6.sandy.scope", }, $ For the common case of the header having a member that has the 'offset' and 'size' members, it is possible to use this more compact form: $ pahole ~/bin/perf --header=perf_file_header --range=data -C 'perf_event_header(sizeof,type,type_enum=perf_event_type,filter=type==PERF_RECORD_CGROUP)' --prettify perf.data This uses ~/bin/perf to get the type definitions, the defines 'struct perf_file_header' as the header, then seeks '$header.data.offset' bytes from the start of the file, and considers '$header.data.size' bytes worth of such records. The filter expression may omit a common prefix, in this case it could additionally be equivalently written as both 'fil- ter=type==CGROUP' or the 'filter=' can also be omitted, getting as compact as 'type==CGROUP': If we look at: $ pahole ~/bin/perf -C perf_event_header struct perf_event_header { __u32 type; /* 0 4 */ __u16 misc; /* 4 2 */ __u16 size; /* 6 2 */ /* size: 8, cachelines: 1, members: 3 */ /* last cacheline: 8 bytes */ }; $ And: $ pahole ~/bin/perf -C perf_event_type enum perf_event_type { PERF_RECORD_MMAP = 1, PERF_RECORD_LOST = 2, PERF_RECORD_COMM = 3, PERF_RECORD_EXIT = 4, PERF_RECORD_THROTTLE = 5, PERF_RECORD_UNTHROTTLE = 6, PERF_RECORD_FORK = 7, PERF_RECORD_READ = 8, PERF_RECORD_SAMPLE = 9, PERF_RECORD_MMAP2 = 10, PERF_RECORD_AUX = 11, PERF_RECORD_ITRACE_START = 12, PERF_RECORD_LOST_SAMPLES = 13, PERF_RECORD_SWITCH = 14, PERF_RECORD_SWITCH_CPU_WIDE = 15, PERF_RECORD_NAMESPACES = 16, PERF_RECORD_KSYMBOL = 17, PERF_RECORD_BPF_EVENT = 18, PERF_RECORD_CGROUP = 19, PERF_RECORD_TEXT_POKE = 20, PERF_RECORD_MAX = 21, }; $ And furthermore: $ pahole ~/bin/perf -C perf_record_cgroup struct perf_record_cgroup { struct perf_event_header header; /* 0 8 */ __u64 id; /* 8 8 */ char path[4096]; /* 16 4096 */ /* size: 4112, cachelines: 65, members: 3 */ /* last cacheline: 16 bytes */ }; $ Then we can see how the perf_event_header.type could be converted from a __u32 to a string (PERF_RECORD_CGROUP). If we remove that type_enum=perf_event_type, we will lose the conversion of 'struct perf_event_header' to the more descriptive 'struct perf_record_cgroup', and also the beautification of the header.type field: $ pahole ~/bin/perf --header=perf_file_header --seek_bytes '$header.data.offset' --size_bytes='$header.data.size' -C 'perf_event_header(sizeof,type,filter=type==19)' --prettify perf.data { .type = 19, .misc = 0, .size = 40, }, { .type = 19, .misc = 0, .size = 48, }, { .type = 19, .misc = 0, .size = 48, }, { .type = 19, .misc = 0, .size = 128, }, { .type = 19, .misc = 0, .size = 88, }, $ Some of the records are not found in 'type_enum=perf_event_type' so some of the records don't get converted to a type that fully shows its contents. For perf we know that those are in another enumeration, 'enum perf_user_event_type', so, for these cases, we can create a 'virtual enum', i.e. the sum of two enums and then get all those entries decoded and prop- erly casted, first few records with just 'enum perf_event_type': $ pahole ~/bin/perf --header=perf_file_header --seek_bytes '$header.data.offset' --size_bytes='$header.data.size' -C 'perf_event_header(sizeof,type,type_enum=perf_event_type)' --count 4 --prettify perf.data { .type = 79, .misc = 0, .size = 32, }, { .type = 73, .misc = 0, .size = 40, }, { .type = 74, .misc = 0, .size = 32, }, { .header = { .type = PERF_RECORD_CGROUP, .misc = 0, .size = 40, }, .id = 1, .path = "/", }, $ Now with both enumerations, i.e. with 'type_enum=perf_event_type+perf_user_event_type': $ pahole ~/bin/perf --header=perf_file_header --seek_bytes '$header.data.offset' --size_bytes='$header.data.size' -C 'perf_event_header(sizeof,type,type_enum=perf_event_type+perf_user_event_type)' --count 5 --prettify perf.data { .header = { .type = PERF_RECORD_TIME_CONV, .misc = 0, .size = 32, }, .time_shift = 31, .time_mult = 1016803377, .time_zero = 435759009518382, }, { .header = { .type = PERF_RECORD_THREAD_MAP, .misc = 0, .size = 40, }, .nr = 1, .entries = 0x50 0x7e 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00, }, { .header = { .type = PERF_RECORD_CPU_MAP, .misc = 0, .size = 32, }, .data = { .type = 1, .data = "", }, }, { .header = { .type = PERF_RECORD_CGROUP, .misc = 0, .size = 40, }, .id = 1, .path = "/", }, { .header = { .type = PERF_RECORD_CGROUP, .misc = 0, .size = 48, }, .id = 1553, .path = "/system.slice", }, $ It is possible to pass multiple types, one has only to make sure they ap- pear in the file in sequence, i.e. for the perf.data example, see the perf_file_header dump above, one can print the perf_file_attr structs in the header attrs range, then the perf_event_header in the data range with the following command: pahole ~/bin/perf --header=perf_file_header -C 'perf_file_attr(range=attrs),perf_event_header(range=data,sizeof,type,type_enum=perf_event_type+perf_user_event_type)' --prettify perf.data SEE ALSO eu-readelf(1), readelf(1), objdump(1). https://www.kernel.org/doc/ols/2007/ols2007v2-pages-35-44.pdf. AUTHOR pahole was written and is maintained by Arnaldo Carvalho de Melo <acme@ker- nel.org>. Thanks to Andrii Nakryiko and Martin KaFai Lau for providing the BTF en- coder and improving the codebase while making sure the BTF encoder works as needed to be used in encoding the Linux kernel .BTF section from the DWARF info generated by gcc. For that Andrii wrote a BTF deduplicator in libbpf that is used by pahole. Also thanks to Conectiva, Mandriva and Red Hat for allowing me to work on these tools. Please send bug reports to <dwarves@vger.kernel.org>. No subscription is required. dwarves January 16, 2020 pahole(1)
NAME | SYNOPSIS | DESCRIPTION | OPTIONS | NOTES | EXAMPLES | PRETTY PRINTING | PRETTY PRINTING EXAMPLES | SEE ALSO | AUTHOR
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