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 --hex Print offsets and sizes in hexadecimal.
63 -r, --rel_offset
66 Show relative offsets of members in inner structs.
67 -p, --expand_pointers
70 Expand class pointer members.
71 -R, --reorganize
74 Reorganize struct, demoting and combining bitfields, moving mem‐
75 bers to remove alignment holes and padding.
76 -S, --show_reorg_steps
79 Show the struct layout at each reorganization step.
80 -i, --contains=CLASS_NAME
83 Show classes that contains CLASS_NAME.
84 -a, --anon_include
87 Include anonymous classes.
88 -A, --nested_anon_include
91 Include nested (inside other structs) anonymous classes.
92 -B, --bit_holes=NR_HOLES
95 Show only structs at least NR_HOLES bit holes.
96 -d, --recursive
99 Recursive mode, affects several other flags.
100 -D, --decl_exclude=PREFIX
103 exclude classes declared in files with PREFIX.
104 -f, --find_pointers_to=CLASS_NAME
107 Find pointers to CLASS_NAME.
108 -H, --holes=NR_HOLES
111 Show only structs with at least NR_HOLES holes.
112 -I, --show_decl_info
115 Show the file and line number where the tags were defined, if
116 available in the debugging information.
117 -l, --show_first_biggest_size_base_type_member
120 Show first biggest size base_type member.
121 -m, --nr_methods
124 Show number of methods.
125 -M, --show_only_data_members
128 Show only the members that use space in the class layout. C++
129 methods will be suppressed.
130 -n, --nr_members
133 Show number of members.
134 -N, --class_name_len
137 Show size of classes.
138 -O, --dwarf_offset=OFFSET
141 Show tag with DWARF OFFSET.
142 -P, --packable
145 Show only structs that has holes that can be packed if members
146 are reorganized, for instance when using the --reorganize
147 option.
148 -q, --quiet
151 Be quieter.
152 -s, --sizes
155 Show size of classes.
156 -t, --separator=SEP
159 Use SEP as the field separator.
160 -T, --nr_definitions
163 Show how many times struct was defined.
164 -u, --defined_in
167 Show CUs where CLASS_NAME (-C) is defined.
168 --flat_arrays
171 Flatten arrays, so that array[10][2] becomes array[20]. Useful
172 when generating from both CTF/BTF and DWARF encodings for the
173 same binary for testing purposes.
174 --suppress_aligned_attribute
177 Suppress forced alignment markers, so that one can compare BTF
178 or CTF output, that don't have that info, to output from DWARF
179 >= 5.
180 --suppress_force_paddings
183 Suppress bitfield forced padding at the end of structs, as this
185 requires something like DWARF's DW_AT_alignment, so that one can
186 compare BTF or CTF output, that don't have that info.
187 --suppress_packed
190 Suppress the output of the inference of
192 __attribute__((__packed__)), so that one can compare BTF or CTF
193 output, the inference algorithm uses things like DW_AT_align‐
194 ment, so until it is improved to infer that as well for BTF,
195 allow disabling this output.
196 --fixup_silly_bitfields
199 Converts silly bitfields such as "int foo:32" to plain "int
200 foo".
201 -V, --verbose
204 be verbose
205 -w, --word_size=WORD_SIZE
208 Change the arch word size to WORD_SIZE.
209 -x, --exclude=PREFIX
212 Exclude PREFIXed classes.
213 -X, --cu_exclude=PREFIX
216 Exclude PREFIXed compilation units.
217 -y, --prefix_filter=PREFIX
220 Include PREFIXed classes.
221 -z, --hole_size_ge=HOLE_SIZE
224 Show only structs with at least one hole greater or equal to
225 HOLE_SIZE.
226
229 To enable the generation of debugging information in the Linux kernel
230 build process select CONFIG_DEBUG_INFO. This can be done using make
231 menuconfig by this path: "Kernel Hacking" -> "Kernel Debugging" ->
232 "Compile the kernel with debug info".
233 Many distributions also come with debuginfo packages, so just enable it
235 in your package manager repository configuration and install the ker‐
236 nel-debuginfo, or any other userspace program written in a language
237 that the compiler generates debuginfo (C, C++, for instance).
238
241 eu-readelf(1), readelf(1), objdump(1).
242 https://www.kernel.org/doc/ols/2007/ols2007v2-pages-35-44.pdf.
244
246 pahole was written by Arnaldo Carvalho de Melo <acme@ghostproto‐
247 cols.net>.
248 Please send bug reports to <dwarves@vger.kernel.org>.
250 No subscription is required.
252dwarves February 13, 2009 pahole(1)