1pahole(1) dwarves pahole(1)
2
6 pahole - Shows, manipulates data structure layout and pretty prints raw
7 data.
8
10 pahole [options] files
11
13 pahole shows data structure layouts encoded in debugging information
14 formats, DWARF, CTF and BTF being supported.
15 This is useful for, among other things: optimizing important data
17 structures by reducing its size, figuring out what is the field sitting
18 at an offset from the start of a data structure, investigating ABI
19 changes and more generally understanding a new codebase you have to
20 work with.
21 It also uses these structure layouts to pretty print data feed to its
23 standard input, e.g.:
24 $ pahole --header elf64_hdr --prettify /lib/modules/5.8.0-rc6+/build/vmlinux
26 {
27 .e_ident = { 127, 69, 76, 70, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
28 .e_type = 2,
29 .e_machine = 62,
30 .e_version = 1,
31 .e_entry = 16777216,
32 .e_phoff = 64,
33 .e_shoff = 604653784,
34 .e_flags = 0,
35 .e_ehsize = 64,
36 .e_phentsize = 56,
37 .e_phnum = 5,
38 .e_shentsize = 64,
39 .e_shnum = 80,
40 .e_shstrndx = 79,
41 },
42 $
43 See the PRETTY PRINTING section for further examples and documentation.
45 The files must have associated debugging information. This information
47 may be inside the file itself, in ELF sections, or in another file.
48 One way to have this information is to specify the -g option to the
50 compiler when building it. When this is done the information will be
51 stored in an ELF section. For the DWARF debugging information format
52 this, adds, among others, the .debug_info ELF section. For CTF it is
53 found in just one ELF section, .SUNW_ctf. BTF comes in at least the
54 .BTF ELF section, and may come also with the .BTF.ext ELF section.
55 The debuginfo packages available in most Linux distributions are also
57 supported by pahole, where the debugging information is available in a
58 separate file.
59 By default, pahole shows the layout of all named structs in the files
61 specified.
62 If no files are specified, then it will look if the /sys/kernel/btf/vm‐
64 linux is present, using the BTF information present in it about the
65 running kernel, i.e. this works:
66 $ pahole list_head
68 struct list_head {
69 struct list_head * next; /* 0 8 */
70 struct list_head * prev; /* 8 8 */
71 /* size: 16, cachelines: 1, members: 2 */
73 /* last cacheline: 16 bytes */
74 };
75 $
76 If BTF is not present and no file is passed, then a vmlinux that
78 matches the build-id for the running kernel will be looked up in the
79 usual places, including where the kernel debuginfo packages put it,
80 looking for DWARF info instead.
81 See the EXAMPLES section for more usage suggestions.
83 It also pretty prints whatever is fed to its standard input, according
85 to the type specified, see the EXAMPLE session.
86 Use --count to state how many records should be pretty printed.
88
91 pahole supports the following options.
92 -C, --class_name=CLASS_NAMES
95 Show just these classes. This can be a comma separated list of
96 class names or file URLs (e.g.: file://class_list.txt)
97 -c, --cacheline_size=SIZE
100 Set cacheline size to SIZE bytes.
101 Sort the output by type name, maybe this will grow to allow sorting by
104 other
105 criteria.
106 This is mostly needed so that pretty printing from BTF and DWARF
108 can be comparable when using using multiple threads to load
109 DWARF data, when the order that the types in the compile units
110 is processed is not deterministic.
111 --count=COUNT
114 Pretty print the first COUNT records from input.
115 --skip=COUNT
118 Skip COUNT input records.
119 -E, --expand_types
122 Expand class members. Useful to find in what member of inner
123 structs where an offset from the beginning of a struct is.
124 -F, --format_path
127 Allows specifying a list of debugging formats to try, in order.
128 Right now this includes "ctf" and "dwarf". The default format
129 path used is equivalent to "-F dwarf,ctf".
130 --hashbits=BITS
133 Allows specifying the number of bits for the debugging format
134 loader to use. The only one affected so far is the "dwarf" one,
135 its default now is 15, the maximum for it is now 21 bits. Tweak
136 it to see if it improves performance as the kernel evolves and
137 more types and functions have to be loaded.
138 --hex Print offsets and sizes in hexadecimal.
141 -r, --rel_offset
144 Show relative offsets of members in inner structs.
145 -p, --expand_pointers
148 Expand class pointer members.
149 -R, --reorganize
152 Reorganize struct, demoting and combining bitfields, moving mem‐
153 bers to remove alignment holes and padding.
154 -S, --show_reorg_steps
157 Show the struct layout at each reorganization step.
158 -i, --contains=CLASS_NAME
161 Show classes that contains CLASS_NAME.
162 -a, --anon_include
165 Include anonymous classes.
166 -A, --nested_anon_include
169 Include nested (inside other structs) anonymous classes.
170 -B, --bit_holes=NR_HOLES
173 Show only structs at least NR_HOLES bit holes.
174 -d, --recursive
177 Recursive mode, affects several other flags.
178 -D, --decl_exclude=PREFIX
181 exclude classes declared in files with PREFIX.
182 -f, --find_pointers_to=CLASS_NAME
185 Find pointers to CLASS_NAME.
186 -H, --holes=NR_HOLES
189 Show only structs with at least NR_HOLES holes.
190 -I, --show_decl_info
193 Show the file and line number where the tags were defined, if
194 available in the debugging information.
195 --skip_encoding_btf_vars
198 Do not encode VARs in BTF.
199 -j, --jobs=N
202 Run N jobs in parallel. Defaults to number of online processors
203 + 10% (like the 'ninja' build system) if no argument is speci‐
204 fied.
205 -J, --btf_encode
208 Encode BTF information from DWARF, used in the Linux kernel
209 build process when CONFIG_DEBUG_INFO_BTF=y is present, intro‐
210 duced in Linux v5.2. Used to implement features such as BPF CO-
211 RE (Compile Once - Run Everywhere).
212 See https://nakryiko.com/posts/bpf-portability-and-co-re/.
214 --btf_encode_detached=FILENAME
217 Same thing as -J/--btf_encode, but storing the raw BTF info into
218 a separate file.
219 --btf_encode_force
222 Ignore those symbols found invalid when encoding BTF.
223 --btf_base=PATH
226 Path to the base BTF file, for instance: vmlinux when encoding
227 kernel module BTF information. This may be inferred when asking
228 for a /sys/kernel/btf/MODULE, when it will be autoconfigured to
229 "/sys/kernel/btf/vmlinux".
230 --btf_gen_floats
233 Allow producing BTF_KIND_FLOAT entries in systems where the vm‐
234 linux DWARF information has float types.
235 --btf_gen_all
238 Allow using all the BTF features supported by pahole.
239 -l, --show_first_biggest_size_base_type_member
242 Show first biggest size base_type member.
243 -m, --nr_methods
246 Show number of methods of all classes, i.e. the number of func‐
247 tions have arguments that are pointers to a given class.
248 To get the number of methods for an specific class, please use:
250 $ pahole --nr_methods | grep -w sock
252 sock 1005
253 $
254 In the above example it used the BTF information in /sys/ker‐
256 nel/btf/vmlinux.
257 -M, --show_only_data_members
260 Show only the members that use space in the class layout. C++
261 methods will be suppressed.
262 -n, --nr_members
265 Show number of members.
266 -N, --class_name_len
269 Show size of classes.
270 -O, --dwarf_offset=OFFSET
273 Show tag with DWARF OFFSET.
274 -P, --packable
277 Show only structs that has holes that can be packed if members
278 are reorganized, for instance when using the --reorganize op‐
279 tion.
280 -P, --with_flexible_array
283 Show only structs that have a flexible array.
284 -q, --quiet
287 Be quieter.
288 -s, --sizes
291 Show size of classes.
292 -t, --separator=SEP
295 Use SEP as the field separator.
296 -T, --nr_definitions
299 Show how many times struct was defined.
300 -u, --defined_in
303 Show CUs where CLASS_NAME (-C) is defined.
304 --flat_arrays
307 Flatten arrays, so that array[10][2] becomes array[20]. Useful
308 when generating from both CTF/BTF and DWARF encodings for the
309 same binary for testing purposes.
310 --suppress_aligned_attribute
313 Suppress forced alignment markers, so that one can compare BTF
314 or CTF output, that don't have that info, to output from DWARF
315 >= 5.
316 --suppress_force_paddings
319 Suppress bitfield forced padding at the end of structs, as this
321 requires something like DWARF's DW_AT_alignment, so that one can
322 compare BTF or CTF output, that don't have that info.
323 --suppress_packed
326 Suppress the output of the inference of __attri‐
328 bute__((__packed__)), so that one can compare BTF or CTF output,
329 the inference algorithm uses things like DW_AT_alignment, so un‐
330 til it is improved to infer that as well for BTF, allow dis‐
331 abling this output.
332 --fixup_silly_bitfields
335 Converts silly bitfields such as "int foo:32" to plain "int
336 foo".
337 -V, --verbose
340 be verbose
341 --ptr_table_stats
344 Print statistics about ptr_table data structures, used to hold
345 all the types, tags and functions data structures, for develop‐
346 ment tuning of such tables, tuned for a typical 2021 vmlinux
347 file.
348 -w, --word_size=WORD_SIZE
351 Change the arch word size to WORD_SIZE.
352 -x, --exclude=PREFIX
355 Exclude PREFIXed classes.
356 -X, --cu_exclude=PREFIX
359 Exclude PREFIXed compilation units.
360 -y, --prefix_filter=PREFIX
363 Include PREFIXed classes.
364 -z, --hole_size_ge=HOLE_SIZE
367 Show only structs with at least one hole greater or equal to
368 HOLE_SIZE.
369 --structs
372 Show only structs, all the other filters apply, i.e. to show
373 just the sizes of all structs combine --structs with --sizes,
374 etc.
375 --packed
378 Show only packed structs, all the other filters apply, i.e. to
379 show just the sizes of all packed structs combine --packed with
380 --sizes, etc.
381 --unions
384 Show only unions, all the other filters apply, i.e. to show just
385 the sizes of all unions combine --union with --sizes, etc.
386 --version
389 Show a traditional string version, i.e.: "v1.18".
390 --numeric_version
393 Show a numeric only version, suitable for use in Makefiles and
394 scripts where one wants to know what if the installed version
395 has some feature, i.e.: 118 instead of "v1.18".
396 --kabi_prefix=STRING
399 When the prefix of the string is STRING, treat the string as
400 STRING.
401
404 To enable the generation of debugging information in the Linux kernel
405 build process select CONFIG_DEBUG_INFO. This can be done using make
406 menuconfig by this path: "Kernel Hacking" -> "Compile-time checks and
407 compiler options" -> "Compile the kernel with debug info". Consider as
408 well enabling CONFIG_DEBUG_INFO_BTF by going thru the aforementioned
409 menuconfig path and then selecting "Generate BTF typeinfo". Most modern
410 distributions with eBPF support should come with that in all its ker‐
411 nels, greatly facilitating the use of pahole.
412 Many distributions also come with debuginfo packages, so just enable it
414 in your package manager repository configuration and install the ker‐
415 nel-debuginfo, or any other userspace program written in a language
416 that the compiler generates debuginfo (C, C++, for instance).
417
420 All the examples here use either /sys/kernel/btf/vmlinux, if present,
421 or lookup a vmlinux file matching the running kernel, using the build-
422 id info found in /sys/kernel/notes to make sure it matches.
423 Show a type:
425 $ pahole -C __u64
427 typedef long long unsigned int __u64;
428 $
429 Works as well if the only argument is a type name:
432 $ pahole raw_spinlock_t
434 typedef struct raw_spinlock raw_spinlock_t;
435 $
436 Multiple types can be passed, separated by commas:
439 $ pahole raw_spinlock_t,raw_spinlock
441 struct raw_spinlock {
442 arch_spinlock_t raw_lock; /* 0 4 */
443 /* size: 4, cachelines: 1, members: 1 */
445 /* last cacheline: 4 bytes */
446 };
447 typedef struct raw_spinlock raw_spinlock_t;
448 $
449 Types can be expanded:
452 $ pahole -E raw_spinlock
454 struct raw_spinlock {
455 /* typedef arch_spinlock_t */ struct qspinlock {
456 union {
457 /* typedef atomic_t */ struct {
458 int counter; /* 0 4 */
459 } val; /* 0 4 */
460 struct {
461 /* typedef u8 -> __u8 */ unsigned char locked; /* 0 1 */
462 /* typedef u8 -> __u8 */ unsigned char pending; /* 1 1 */
463 }; /* 0 2 */
464 struct {
465 /* typedef u16 -> __u16 */ short unsigned int locked_pending; /* 0 2 */
466 /* typedef u16 -> __u16 */ short unsigned int tail; /* 2 2 */
467 }; /* 0 4 */
468 }; /* 0 4 */
469 } raw_lock; /* 0 4 */
470 /* size: 4, cachelines: 1, members: 1 */
472 /* last cacheline: 4 bytes */
473 };
474 $
475 When decoding OOPSes you may want to see the offsets and sizes in hexa‐
478 decimal:
479 $ pahole --hex thread_struct
481 struct thread_struct {
482 struct desc_struct tls_array[3]; /* 0 0x18 */
483 long unsigned int sp; /* 0x18 0x8 */
484 short unsigned int es; /* 0x20 0x2 */
485 short unsigned int ds; /* 0x22 0x2 */
486 short unsigned int fsindex; /* 0x24 0x2 */
487 short unsigned int gsindex; /* 0x26 0x2 */
488 long unsigned int fsbase; /* 0x28 0x8 */
489 long unsigned int gsbase; /* 0x30 0x8 */
490 struct perf_event * ptrace_bps[4]; /* 0x38 0x20 */
491 /* --- cacheline 1 boundary (64 bytes) was 24 bytes ago --- */
492 long unsigned int debugreg6; /* 0x58 0x8 */
493 long unsigned int ptrace_dr7; /* 0x60 0x8 */
494 long unsigned int cr2; /* 0x68 0x8 */
495 long unsigned int trap_nr; /* 0x70 0x8 */
496 long unsigned int error_code; /* 0x78 0x8 */
497 /* --- cacheline 2 boundary (128 bytes) --- */
498 struct io_bitmap * io_bitmap; /* 0x80 0x8 */
499 long unsigned int iopl_emul; /* 0x88 0x8 */
500 mm_segment_t addr_limit; /* 0x90 0x8 */
501 unsigned int sig_on_uaccess_err:1; /* 0x98: 0 0x4 */
502 unsigned int uaccess_err:1; /* 0x98:0x1 0x4 */
503 /* XXX 30 bits hole, try to pack */
505 /* XXX 36 bytes hole, try to pack */
506 /* --- cacheline 3 boundary (192 bytes) --- */
508 struct fpu fpu; /* 0xc0 0x1040 */
509 /* size: 4352, cachelines: 68, members: 20 */
511 /* sum members: 4312, holes: 1, sum holes: 36 */
512 /* sum bitfield members: 2 bits, bit holes: 1, sum bit holes: 30 bits */
513 };
514 $
515 OK, I know the offset that causes its a 'struct thread_struct' and that
518 the offset is 0x178, so must be in that 'fpu' struct... No problem, ex‐
519 pand 'struct thread_struct' and combine with grep:
520 $ pahole --hex -E thread_struct | egrep '(0x178|struct fpu)' -B4 -A4
522 /* XXX 30 bits hole, try to pack */
523 /* XXX 36 bytes hole, try to pack */
524 /* --- cacheline 3 boundary (192 bytes) --- */
526 struct fpu {
527 unsigned int last_cpu; /* 0xc0 0x4 */
528 /* XXX 4 bytes hole, try to pack */
530 --
532 /* typedef u8 -> __u8 */ unsigned char alimit; /* 0x171 0x1 */
533 /* XXX 6 bytes hole, try to pack */
535 struct math_emu_info * info; /* 0x178 0x8 */
537 /* --- cacheline 6 boundary (384 bytes) --- */
538 /* typedef u32 -> __u32 */ unsigned int entry_eip; /* 0x180 0x4 */
539 } soft; /* 0x100 0x88 */
540 struct xregs_state {
541 $
542 Want to know where 'struct thread_struct' is defined in the kernel
545 sources?
546 $ pahole -I thread_struct | head -2
548 /* Used at: /sys/kernel/btf/vmlinux */
549 /* <0> (null):0 */
550 $
551 Not present in BTF, so use DWARF, takes a little bit longer, and assum‐
554 ing it finds the matching vmlinux file:
555 $ pahole -Fdwarf -I thread_struct | head -2
557 /* Used at: /home/acme/git/linux/arch/x86/kernel/head64.c */
558 /* <3333> /home/acme/git/linux/arch/x86/include/asm/processor.h:485 */
559 $
560 To find the biggest data structures in the Linux kernel:
563 $ pahole -s | sort -k2 -nr | head -5
565 cmp_data 290904 1
566 dec_datas 274520 1
567 cpu_entry_area 217088 0
568 pglist_data 172928 4
569 saved_cmdlines_buffer 131104 1
570 $
571 The second column is the size in bytes and the third is the number of
573 alignment holes in that structure.
574 Show data structures that have a raw spinlock and are related to the
576 RCU mechanism:
577 $ pahole --contains raw_spinlock_t --prefix rcu
579 rcu_node
580 rcu_data
581 rcu_state
582 $
583 To see that in context, combine it with grep:
585 $ pahole rcu_state | grep raw_spinlock_t -B1 -A5
587 /* --- cacheline 52 boundary (3328 bytes) --- */
588 raw_spinlock_t ofl_lock; /* 3328 4 */
589 /* size: 3392, cachelines: 53, members: 35 */
591 /* sum members: 3250, holes: 7, sum holes: 82 */
592 /* padding: 60 */
593 };
594 $
595
598 pahole can also use the data structure types to pretty print raw data
599 specified via --prettify. To consume raw data from the standard input,
600 just use '--prettify -'
601 It can also pretty print raw data from stdin according to the type
603 specified:
604 $ pahole -C modversion_info drivers/scsi/sg.ko
606 struct modversion_info {
607 long unsigned int crc; /* 0 8 */
608 char name[56]; /* 8 56 */
609 /* size: 64, cachelines: 1, members: 2 */
611 };
612 $
613 $ objcopy -O binary --only-section=__versions drivers/scsi/sg.ko versions
614 $
615 $ ls -la versions
616 -rw-rw-r--. 1 acme acme 7616 Jun 25 11:33 versions
617 $
618 $ pahole --count 3 -C modversion_info drivers/scsi/sg.ko --prettify versions
619 {
620 .crc = 0x8dabd84,
621 .name = "module_layout",
622 },
623 {
624 .crc = 0x45e4617b,
625 .name = "no_llseek",
626 },
627 {
628 .crc = 0xa23fae8c,
629 .name = "param_ops_int",
630 },
631 $
632 $ pahole --skip 1 --count 2 -C modversion_info drivers/scsi/sg.ko --prettify - < versions
633 {
634 .crc = 0x45e4617b,
635 .name = "no_llseek",
636 },
637 {
638 .crc = 0xa23fae8c,
639 .name = "param_ops_int",
640 },
641 $
642 This is equivalent to:
643 $ pahole --seek_bytes 64 --count 1 -C modversion_info drivers/scsi/sg.ko --prettify versions
645 {
646 .crc = 0x45e4617b,
647 .name = "no_llseek",
648 },
649 $
650 -C, --class_name=CLASS_NAME
652 Pretty print according to this class. Arguments may be passed to
653 it to affect how the pretty printing is performed, e.g.:
654 -C 'perf_event_header(sizeof,type,type_enum=perf_event_type,filter=type==PERF_RECORD_EXIT)'
657 This would select the 'struct perf_event_header' as the type to use to
659 pretty print records states that the 'size' field in that struct should
660 be used to figure out the size of the record (variable sized records),
661 that the 'enum perf_event_type' should be used to pretty print the nu‐
662 meric value in perf_event_header->type and furthermore that it should
663 be used to heuristically look for structs with the same name (lower‐
664 case) of the enum entry that is converted from the type field, using it
665 to pretty print instead of the base 'perf_event_header' type. See the
666 PRETTY PRINTING EXAMPLES section below.
667 Furthermore the 'filter=' part can be used, so far with only the '=='
669 operator to filter based on the 'type' field and converting the string
670 'PERF_RECORD_EXIT' to a number according to type_enum.
671 The 'sizeof' arg defaults to the 'size' member name, if the name is
673 different, one can use
674 'sizeof=sz' form, ditto for 'type=other_member_name' field, that de‐
675 faults to 'type'.
676
679 Looking at the ELF header for a vmlinux file, using BTF, first lets
680 discover the ELF header type:
681 $ pahole --sizes | grep -i elf | grep -i _h
683 elf64_hdr 64 0
684 elf32_hdr 52 0
685 $
686 Now we can use this to show the first record from offset zero:
688 $ pahole -C elf64_hdr --count 1 --prettify /lib/modules/5.8.0-rc3+/build/vmlinux
690 {
691 .e_ident = { 127, 69, 76, 70, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0 },
692 .e_type = 2,
693 .e_machine = 62,
694 .e_version = 1,
695 .e_entry = 16777216,
696 .e_phoff = 64,
697 .e_shoff = 775923840,
698 .e_flags = 0,
699 .e_ehsize = 64,
700 .e_phentsize = 56,
701 .e_phnum = 5,
702 .e_shentsize = 64,
703 .e_shnum = 80,
704 .e_shstrndx = 79,
705 },
706 $
707 This is equivalent to:
709 $ pahole --header elf64_hdr --prettify /lib/modules/5.8.0-rc3+/build/vmlinux
711 The --header option also allows reference in other command line options
713 to fields in the header. This is useful when one wants to show multi‐
714 ple records in a file and the range where those fields are located is
715 specified in header fields, such as for perf.data files:
716 $ pahole --hex ~/bin/perf --header perf_file_header --prettify perf.data
718 {
719 .magic = 0x32454c4946524550,
720 .size = 0x68,
721 .attr_size = 0x88,
722 .attrs = {
723 .offset = 0xa8,
724 .size = 0x88,
725 },
726 .data = {
727 .offset = 0x130,
728 .size = 0x588,
729 },
730 .event_types = {
731 .offset = 0,
732 .size = 0,
733 },
734 .adds_features = { 0x16717ffc, 0, 0, 0 },
735 },
736 $
737 So to display the cgroups records in the perf_file_header.data section
739 we can use:
740 $ 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
742 {
743 .header = {
744 .type = PERF_RECORD_CGROUP,
745 .misc = 0,
746 .size = 40,
747 },
748 .id = 1,
749 .path = "/",
750 },
751 {
752 .header = {
753 .type = PERF_RECORD_CGROUP,
754 .misc = 0,
755 .size = 48,
756 },
757 .id = 1553,
758 .path = "/system.slice",
759 },
760 {
761 .header = {
762 .type = PERF_RECORD_CGROUP,
763 .misc = 0,
764 .size = 48,
765 },
766 .id = 8,
767 .path = "/machine.slice",
768 },
769 {
770 .header = {
771 .type = PERF_RECORD_CGROUP,
772 .misc = 0,
773 .size = 128,
774 },
775 .id = 7828,
776 .path = "/machine.slice/libpod-42be8e8d4eb9d22405845005f0d04ea398548dccc934a150fbaa3c1f1f9492c2.scope",
777 },
778 {
779 .header = {
780 .type = PERF_RECORD_CGROUP,
781 .misc = 0,
782 .size = 88,
783 },
784 .id = 13,
785 .path = "/machine.slice/machine-qemud1drhel6.sandy.scope",
786 },
787 $
788 For the common case of the header having a member that has the 'offset'
790 and 'size' members, it is possible to use this more compact form:
791 $ 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
793 This uses ~/bin/perf to get the type definitions, the defines 'struct
795 perf_file_header' as the header, then seeks '$header.data.offset' bytes
796 from the start of the file, and considers '$header.data.size' bytes
797 worth of such records. The filter expression may omit a common prefix,
798 in this case it could additonally be equivalently written as both 'fil‐
799 ter=type==CGROUP' or the 'filter=' can also be omitted, getting as com‐
800 pact as 'type==CGROUP':
801 If we look at:
803 $ pahole ~/bin/perf -C perf_event_header
805 struct perf_event_header {
806 __u32 type; /* 0 4 */
807 __u16 misc; /* 4 2 */
808 __u16 size; /* 6 2 */
809 /* size: 8, cachelines: 1, members: 3 */
811 /* last cacheline: 8 bytes */
812 };
813 $
814 And:
816 $ pahole ~/bin/perf -C perf_event_type
818 enum perf_event_type {
819 PERF_RECORD_MMAP = 1,
820 PERF_RECORD_LOST = 2,
821 PERF_RECORD_COMM = 3,
822 PERF_RECORD_EXIT = 4,
823 PERF_RECORD_THROTTLE = 5,
824 PERF_RECORD_UNTHROTTLE = 6,
825 PERF_RECORD_FORK = 7,
826 PERF_RECORD_READ = 8,
827 PERF_RECORD_SAMPLE = 9,
828 PERF_RECORD_MMAP2 = 10,
829 PERF_RECORD_AUX = 11,
830 PERF_RECORD_ITRACE_START = 12,
831 PERF_RECORD_LOST_SAMPLES = 13,
832 PERF_RECORD_SWITCH = 14,
833 PERF_RECORD_SWITCH_CPU_WIDE = 15,
834 PERF_RECORD_NAMESPACES = 16,
835 PERF_RECORD_KSYMBOL = 17,
836 PERF_RECORD_BPF_EVENT = 18,
837 PERF_RECORD_CGROUP = 19,
838 PERF_RECORD_TEXT_POKE = 20,
839 PERF_RECORD_MAX = 21,
840 };
841 $
842 And furthermore:
844 $ pahole ~/bin/perf -C perf_record_cgroup
846 struct perf_record_cgroup {
847 struct perf_event_header header; /* 0 8 */
848 __u64 id; /* 8 8 */
849 char path[4096]; /* 16 4096 */
850 /* size: 4112, cachelines: 65, members: 3 */
852 /* last cacheline: 16 bytes */
853 };
854 $
855 Then we can see how the perf_event_header.type could be converted from
857 a __u32 to a string (PERF_RECORD_CGROUP). If we remove that
858 type_enum=perf_event_type, we will lose the conversion of 'struct
859 perf_event_header' to the more descriptive 'struct perf_record_cgroup',
860 and also the beautification of the header.type field:
861 $ 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
863 {
864 .type = 19,
865 .misc = 0,
866 .size = 40,
867 },
868 {
869 .type = 19,
870 .misc = 0,
871 .size = 48,
872 },
873 {
874 .type = 19,
875 .misc = 0,
876 .size = 48,
877 },
878 {
879 .type = 19,
880 .misc = 0,
881 .size = 128,
882 },
883 {
884 .type = 19,
885 .misc = 0,
886 .size = 88,
887 },
888 $
889 Some of the records are not found in 'type_enum=perf_event_type' so
891 some of the records don't get converted to a type that fully shows its
892 contents. For perf we know that those are in another enumeration, 'enum
893 perf_user_event_type', so, for these cases, we can create a 'virtual
894 enum', i.e. the sum of two enums and then get all those entries decoded
895 and properly casted, first few records with just 'enum
896 perf_event_type':
897 $ 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
899 {
900 .type = 79,
901 .misc = 0,
902 .size = 32,
903 },
904 {
905 .type = 73,
906 .misc = 0,
907 .size = 40,
908 },
909 {
910 .type = 74,
911 .misc = 0,
912 .size = 32,
913 },
914 {
915 .header = {
916 .type = PERF_RECORD_CGROUP,
917 .misc = 0,
918 .size = 40,
919 },
920 .id = 1,
921 .path = "/",
922 },
923 $
924 Now with both enumerations, i.e. with
926 'type_enum=perf_event_type+perf_user_event_type':
927 $ 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
929 {
930 .header = {
931 .type = PERF_RECORD_TIME_CONV,
932 .misc = 0,
933 .size = 32,
934 },
935 .time_shift = 31,
936 .time_mult = 1016803377,
937 .time_zero = 435759009518382,
938 },
939 {
940 .header = {
941 .type = PERF_RECORD_THREAD_MAP,
942 .misc = 0,
943 .size = 40,
944 },
945 .nr = 1,
946 .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,
947 },
948 {
949 .header = {
950 .type = PERF_RECORD_CPU_MAP,
951 .misc = 0,
952 .size = 32,
953 },
954 .data = {
955 .type = 1,
956 .data = "",
957 },
958 },
959 {
960 .header = {
961 .type = PERF_RECORD_CGROUP,
962 .misc = 0,
963 .size = 40,
964 },
965 .id = 1,
966 .path = "/",
967 },
968 {
969 .header = {
970 .type = PERF_RECORD_CGROUP,
971 .misc = 0,
972 .size = 48,
973 },
974 .id = 1553,
975 .path = "/system.slice",
976 },
977 $
978 It is possible to pass multiple types, one has only to make sure they
980 appear in the file in sequence, i.e. for the perf.data example, see the
981 perf_file_header dump above, one can print the perf_file_attr structs
982 in the header attrs range, then the perf_event_header in the data range
983 with the following command:
984 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
986
989 eu-readelf(1), readelf(1), objdump(1).
990 https://www.kernel.org/doc/ols/2007/ols2007v2-pages-35-44.pdf.
992
994 pahole was written and is maintained by Arnaldo Carvalho de Melo
995 <acme@kernel.org>.
996 Thanks to Andrii Nakryiko and Martin KaFai Lau for providing the BTF
998 encoder and improving the codebase while making sure the BTF encoder
999 works as needed to be used in encoding the Linux kernel .BTF section
1000 from the DWARF info generated by gcc. For that Andrii wrote a BTF dedu‐
1001 plicator in libbpf that is used by pahole.
1002 Also thanks to Conectiva, Mandriva and Red Hat for allowing me to work
1004 on these tools.
1005 Please send bug reports to <dwarves@vger.kernel.org>.
1007 No subscription is required.
1009dwarves January 16, 2020 pahole(1)