1pahole(1) dwarves pahole(1)
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6 pahole - Shows and manipulates data structure layout.
7
9 pahole [options] files
10
12 pahole shows data structure layouts encoded in debugging information
13 formats, DWARF and CTF being supported.
14 This is useful for, among other things: optimizing important data
16 structures by reducing its size, figuring out what is the field sitting
17 at an offset from the start of a data structure, investigating ABI
18 changes and more generally understanding a new codebase you have to
19 work with.
20 The files must have associated debugging information. This information
22 may be inside the file itself, in ELF sections, or in another file.
23 One way to have this information is to specify the -g option to the
25 compiler when building it. When this is done the information will be
26 stored in an ELF section. For the DWARF debugging information format
27 this, adds, among others, the .debug_info ELF section. For CTF it is
28 found in just one ELF section, .SUNW_ctf.
29 The debuginfo packages available in most Linux distributions are also
31 supported by pahole, where the debugging information is available in a
32 separate file.
33 By default, pahole shows the layout of all named structs in the files
35 specified.
36
39 pahole supports the following options.
40 -C, --class_name=CLASS_NAMES
43 Show just these classes. This can be a comma separated list of
44 class names or file URLs (e.g.: file://class_list.txt)
45 -c, --cacheline_size=SIZE
48 Set cacheline size to SIZE bytes.
49 -E, --expand_types
52 Expand class members. Useful to find in what member of inner
53 structs where an offset from the beginning of a struct is.
54 -F, --format_path
57 Allows specifying a list of debugging formats to try, in order.
58 Right now this includes "ctf" and "dwarf". The default format
59 path used is equivalent to "-F dwarf,ctf".
60 -r, --rel_offset
63 Show relative offsets of members in inner structs.
64 -p, --expand_pointers
67 Expand class pointer members.
68 -R, --reorganize
71 Reorganize struct, demoting and combining bitfields, moving mem‐
72 bers to remove alignment holes and padding.
73 -S, --show_reorg_steps
76 Show the struct layout at each reorganization step.
77 -i, --contains=CLASS_NAME
80 Show classes that contains CLASS_NAME.
81 -a, --anon_include
84 Include anonymous classes.
85 -A, --nested_anon_include
88 Include nested (inside other structs) anonymous classes.
89 -B, --bit_holes=NR_HOLES
92 Show only structs at least NR_HOLES bit holes.
93 -d, --recursive
96 Recursive mode, affects several other flags.
97 -D, --decl_exclude=PREFIX
100 exclude classes declared in files with PREFIX.
101 -f, --find_pointers_to=CLASS_NAME
104 Find pointers to CLASS_NAME.
105 -H, --holes=NR_HOLES
108 Show only structs with at least NR_HOLES holes.
109 -I, --show_decl_info
112 Show the file and line number where the tags were defined, if
113 available in the debugging information.
114 -l, --show_first_biggest_size_base_type_member
117 Show first biggest size base_type member.
118 -m, --nr_methods
121 Show number of methods.
122 -M, --show_only_data_members
125 Show only the members that use space in the class layout. C++
126 methods will be suppressed.
127 -n, --nr_members
130 Show number of members.
131 -N, --class_name_len
134 Show size of classes.
135 -O, --dwarf_offset=OFFSET
138 Show tag with DWARF OFFSET.
139 -P, --packable
142 Show only structs that has holes that can be packed if members
143 are reorganized, for instance when using the --reorganize
144 option.
145 -q, --quiet
148 Be quieter.
149 -s, --sizes
152 Show size of classes.
153 -t, --separator=SEP
156 Use SEP as the field separator.
157 -T, --nr_definitions
160 Show how many times struct was defined.
161 -u, --defined_in
164 Show CUs where CLASS_NAME (-C) is defined.
165 --flat_arrays
168 Flatten arrays, so that array[10][2] becomes array[20]. Useful
169 when generating from both CTF and DWARF encodings for the same
170 binary for testing purposes.
171 --fixup_silly_bitfields
174 Converts silly bitfields such as "int foo:32" to plain "int
175 foo".
176 -V, --verbose
179 be verbose
180 -w, --word_size=WORD_SIZE
183 Change the arch word size to WORD_SIZE.
184 -x, --exclude=PREFIX
187 Exclude PREFIXed classes.
188 -X, --cu_exclude=PREFIX
191 Exclude PREFIXed compilation units.
192 -y, --prefix_filter=PREFIX
195 Include PREFIXed classes.
196 -z, --hole_size_ge=HOLE_SIZE
199 Show only structs with at least one hole greater or equal to
200 HOLE_SIZE.
201
204 To enable the generation of debugging information in the Linux kernel
205 build process select CONFIG_DEBUG_INFO. This can be done using make
206 menuconfig by this path: "Kernel Hacking" -> "Kernel Debugging" ->
207 "Compile the kernel with debug info".
208 Many distributions also come with debuginfo packages, so just enable it
210 in your package manager repository configuration and install the ker‐
211 nel-debuginfo, or any other userspace program written in a language
212 that the compiler generates debuginfo (C, C++, for instance).
213
216 eu-readelf(1), readelf(1), objdump(1).
217 http://oops.ghostprotocols.net:81/acme/7dwarves.pdf.
219
221 pahole was written by Arnaldo Carvalho de Melo <acme@ghostproto‐
222 cols.net>.
223 Please send bug reports to <dwarves@vger.kernel.org>.
225 No subscription is required.
227dwarves February 13, 2009 pahole(1)