NAME

       pahole - Shows and manipulates data structure layout.

SYNOPSIS

       pahole [options] files

DESCRIPTION

       pahole  shows  data  structure  layouts  encoded  in  debugging  information formats, DWARF and CTF being
       supported.

       This is useful for, among other things: optimizing  important  data  structures  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.

       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 compiler 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.

       The debuginfo packages available in most Linux distributions are also  supported  by  pahole,  where  the
       debugging information is available in a separate file.

       By default, pahole shows the layout of all named structs in the files specified.

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.

       -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 "ctf" and
              "dwarf". The default format path used is equivalent to "-F dwarf,ctf".

       -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.

       -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.

       -I, --show_decl_info
              Show  the  file  and  line  number  where  the  tags  were  defined, if available in the debugging
              information.

       -l, --show_first_biggest_size_base_type_member
              Show first biggest size base_type member.

       -m, --nr_methods
              Show number of methods.

       -M, --show_only_data_members
              Show only the members that use space in the class layout. C++ methods 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.

       -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 and
              DWARF encodings for the same binary for testing purposes.

       --fixup_silly_bitfields
              Converts silly bitfields such as "int foo:32" to plain "int foo".

       -V, --verbose
              be verbose

       -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.

       -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.

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" -> "Kernel
       Debugging" -> "Compile the kernel with debug info".

       Many distributions also come with  debuginfo  packages,  so  just  enable  it  in  your  package  manager
       repository  configuration  and  install the kernel-debuginfo, or any other userspace program written in a
       language that the compiler generates debuginfo (C, C++, for instance).

SEE ALSO

       eu-readelf(1), readelf(1), objdump(1).

       http://oops.ghostprotocols.net:81/acme/7dwarves.pdf.

AUTHOR

       pahole was written by Arnaldo Carvalho de Melo <acme@ghostprotocols.net>.

       Please send bug reports to <dwarves@vger.kernel.org>.

       No subscription is required.