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1 perry 1 KALLSYMS
2 !!!KALLSYMS
3 NAME
4 SYNOPSIS
5 DESCRIPTION
6 OPTIONS
7 LINKER PASSES
8 DATA FORMAT
9 SEE ALSO
10 HISTORY
11 ----
12 !!NAME
13
14
15 kallsyms - Extract all kernel symbols for debugging
16 !!SYNOPSIS
17
18
19 __kallsyms__ [[-Vh] kernel_filename
20 !!DESCRIPTION
21
22
23 __Kallsyms__ extracts all the non-stack symbols from a
24 kernel and builds a data blob that can be linked into that
25 kernel for use by debuggers.
26
27
28 A normal kernel only exports symbols that are used by
29 modules. For debugging you may want a list of all the
30 non-stack symbols, not just the exported ones.
31 __kallsyms__ extracts all sections and symbols from a
32 kernel, constructs a list of the sections, symbols and their
33 addresses and writes a relocatable object containing just
34 the __kallsyms section. After the __kallsyms section is
35 linked into the kernel and the kernel has been booted, any
36 debugger can use the data in the __kallsyms section to get
37 better symbol resolution.
38
39
40 For example, a debugger can use the __kallsyms data to
41 resolve a kernel address to:
42
43
44 *
45
46
47 The owning kernel or module.
48
49
50 *
51
52
53 The section within the owning code.
54
55
56 *
57
58
59 The nearest symbol.
60 !!OPTIONS
61
62
63 __-h__, __--help__
64
65
66 Display a summary of options and exit.
67
68
69 __-V__, __--version__
70
71
72 Display the version of __kallsyms__ and
73 exit.
74 !!LINKER PASSES
75
76
77 To create a kernel containing an accurate __kallsyms
78 section, you have to make four linker passes instead of the
79 normal single link step. kallsyms and the linker are fast,
80 the three extra steps take a few seconds on a
81 P200.
82
83
84 1
85
86
87 The initial build of the kernel, without any __kallsyms
88 data. Run __kallsyms__ against the output of this link,
89 creating a relocatable object which contains all the
90 sections and symbols in the raw kernel.
91
92
93 2
94
95
96 Link the kernel again, this time including the
97 __kallsyms__ output from step (1). Adding the __kallsyms
98 section changes the number of sections and many of the
99 kernel symbol offsets so run __kallsyms__ again against
100 the second link, again saving the relocatable
101 output.
102
103
104 3
105
106
107 Link the kernel again, this time including the
108 __kallsyms__ output from step (2). Run __kallsyms__
109 against the latest version of the kernel. The size and
110 position of the __kallsyms section on this run is now
111 stable, none of the kernel sections or symbols will change
112 after this run. The __kallsyms__ output contains the
113 final values of the kernel symbols.
114
115
116 4
117
118
119 Link the final kernel, including the __kallsyms__ output
120 from step (3).
121 !!DATA FORMAT
122
123
124 The __kallsyms section is a bit unusual. It deliberately has
125 no relocatable data, all
126
127
128 ''/usr/include/sys/kallsyms.h'' contains the mappings for
129 the __kallsyms data.
130
131
132 __Header__
133
134
135 *
136
137
138 Size of header.
139
140
141 *
142
143
144 Total size of the __kallsyms data, including
145 strings.
146
147
148 *
149
150
151 Number of sections. This only included sections which are
152 loaded into memory.
153
154
155 *
156
157
158 Offset to the first section entry from start of the
159 __kallsyms header.
160
161
162 *
163
164
165 Size of each section entry, excluding the name
166 string.
167
168
169 *
170
171
172 Number of symbols.
173
174
175 *
176
177
178 Offset to the first symbol entry from the start of the
179 __kallsyms header.
180
181
182 *
183
184
185 Size of each symbol entry, excluding the name
186 string.
187
188
189 *
190
191
192 Offset to the first string from the start of the __kallsyms
193 header.
194
195
196 *
197
198
199 Start address of the first section[[1].
200
201
202 *
203
204
205 End address of the last section[[1].
206
207
208 __Section entry__
209
210
211 One entry per loaded section. Since __kallsyms is a loaded
212 section, if the input file contains a __kallsyms section
213 then it is included in this list.
214
215
216 *
217
218
219 Start of the section within the kernel[[1].
220
221
222 *
223
224
225 Size of section.
226
227
228 *
229
230
231 Offset to the name of section, from the start of the
232 __kallsyms strings.
233
234
235 *
236
237
238 Section flags, from the original Elf section.
239
240
241 __Symbol entry__
242
243
244 One per symbol in the input file. Only symbols that fall
245 within loaded sections are stored.
246
247
248 *
249
250
251 Offset to the __kallsyms section entry that this symbol
252 falls within. The offset is from the start of the __kallsyms
253 section entries.
254
255
256 *
257
258
259 Address of the symbol within the kernel[[1]. The symbols are
260 sorted in ascending order on this field.
261
262
263 *
264
265
266 Offset to the name of symbol, from the start of the
267 __kallsyms strings.
268
269
270 __Strings__
271
272
273 A set of NUL terminated strings. Each name is referenced
274 using an offset from the start of the __kallsyms string
275 area.
276
277
278 __Note [[1]__
279
280
281 These fields are exceptions to the
282 !!SEE ALSO
283
284
285 insmod(8).
286 !!HISTORY
287
288
289 Initial version by Keith Owens
290 ----
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