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2d6c6dd1 | 1 | .\" %%%LICENSE_START(PUBLIC_DOMAIN) |
fea681da | 2 | .\" This is in the public domain |
2d6c6dd1 | 3 | .\" %%%LICENSE_END |
6a717e5e | 4 | .\" |
31a1b45e | 5 | .TH LD.SO 8 2017-03-13 "GNU" "Linux Programmer's Manual" |
fea681da | 6 | .SH NAME |
01078c2d | 7 | ld.so, ld-linux.so \- dynamic linker/loader |
a1d5f77c | 8 | .SH SYNOPSIS |
cd6dddf6 | 9 | The dynamic linker can be run either indirectly by running some |
43151de3 MK |
10 | dynamically linked program or shared object |
11 | (in which case no command-line options | |
a1d5f77c MK |
12 | to the dynamic linker can be passed and, in the ELF case, the dynamic linker |
13 | which is stored in the | |
14 | .B .interp | |
15 | section of the program is executed) or directly by running: | |
16 | .P | |
17 | .I /lib/ld-linux.so.* | |
18 | [OPTIONS] [PROGRAM [ARGUMENTS]] | |
fea681da MK |
19 | .SH DESCRIPTION |
20 | The programs | |
21 | .B ld.so | |
22 | and | |
23 | .B ld-linux.so* | |
43151de3 MK |
24 | find and load the shared objects (shared libraries) needed by a program, |
25 | prepare the program to run, and then run it. | |
fea681da MK |
26 | .LP |
27 | Linux binaries require dynamic linking (linking at run time) | |
28 | unless the | |
29 | .B \-static | |
30 | option was given to | |
f19a0f03 | 31 | .BR ld (1) |
fea681da MK |
32 | during compilation. |
33 | .LP | |
34 | The program | |
35 | .B ld.so | |
36 | handles a.out binaries, a format used long ago; | |
37 | .B ld-linux.so* | |
d8d00ab7 MK |
38 | (\fI/lib/ld-linux.so.1\fP for libc5, \fI/lib/ld-linux.so.2\fP for glibc2) |
39 | handles ELF, | |
40 | which everybody has been using for years now. | |
2b9b829d | 41 | Otherwise, both have the same behavior, and use the same |
fea681da MK |
42 | support files and programs |
43 | .BR ldd (1), | |
9af134cd | 44 | .BR ldconfig (8), |
fea681da MK |
45 | and |
46 | .IR /etc/ld.so.conf . | |
47 | .LP | |
43151de3 | 48 | When resolving shared object dependencies, |
15d116d5 MK |
49 | the dynamic linker first inspects each dependency |
50 | string to see if it contains a slash (this can occur if | |
43151de3 | 51 | a shared object pathname containing slashes was specified at link time). |
15d116d5 MK |
52 | If a slash is found, then the dependency string is interpreted as |
53 | a (relative or absolute) pathname, | |
43151de3 | 54 | and the shared object is loaded using that pathname. |
15d116d5 | 55 | .LP |
43151de3 | 56 | If a shared object dependency does not contain a slash, |
15d116d5 | 57 | then it is searched for in the following order: |
cd6dddf6 | 58 | .IP o 3 |
dc4b358f | 59 | Using the directories specified in the |
cd6dddf6 | 60 | DT_RPATH dynamic section attribute |
fea681da MK |
61 | of the binary if present and DT_RUNPATH attribute does not exist. |
62 | Use of DT_RPATH is deprecated. | |
63 | .IP o | |
64 | Using the environment variable | |
24fb0923 MK |
65 | .BR LD_LIBRARY_PATH |
66 | (unless the executable is being run in secure-execution mode; see below). | |
880f5b4b | 67 | in which case it is ignored. |
fea681da | 68 | .IP o |
dc4b358f | 69 | Using the directories specified in the |
cd6dddf6 | 70 | DT_RUNPATH dynamic section attribute |
fea681da MK |
71 | of the binary if present. |
72 | .IP o | |
73 | From the cache file | |
de6d7600 | 74 | .IR /etc/ld.so.cache , |
43151de3 | 75 | which contains a compiled list of candidate shared objects previously found |
c13182ef | 76 | in the augmented library path. |
cd6dddf6 | 77 | If, however, the binary was linked with the |
4d9b6984 | 78 | .B \-z nodeflib |
43151de3 MK |
79 | linker option, shared objects in the default paths are skipped. |
80 | Shared objects installed in hardware capability directories (see below) | |
81 | are preferred to other shared objects. | |
fea681da MK |
82 | .IP o |
83 | In the default path | |
8478ee02 | 84 | .IR /lib , |
fea681da | 85 | and then |
8478ee02 | 86 | .IR /usr/lib . |
39a15561 | 87 | (On some 64-bit architectures, the default paths for 64-bit shared objects are |
b9359c7a MK |
88 | .IR /lib64 , |
89 | and then | |
90 | .IR /usr/lib64 .) | |
cd6dddf6 | 91 | If the binary was linked with the |
4d9b6984 | 92 | .B \-z nodeflib |
fea681da | 93 | linker option, this step is skipped. |
eeb25d47 | 94 | .SS Rpath token expansion |
0a216931 MK |
95 | .PP |
96 | .B ld.so | |
99194a09 MK |
97 | understands certain token strings in an rpath specification |
98 | (DT_RPATH or DT_RUNPATH). | |
99 | Those strings are substituted as follows: | |
eeb25d47 MK |
100 | .TP |
101 | .IR $ORIGIN " (or equivalently " ${ORIGIN} ) | |
8a94e783 | 102 | This expands to |
43151de3 | 103 | the directory containing the program or shared object. |
0a216931 MK |
104 | Thus, an application located in |
105 | .I somedir/app | |
106 | could be compiled with | |
eeb25d47 | 107 | |
5c977011 | 108 | gcc \-Wl,\-rpath,\(aq$ORIGIN/../lib\(aq |
eeb25d47 | 109 | |
43151de3 | 110 | so that it finds an associated shared object in |
0a216931 | 111 | .I somedir/lib |
988db661 MK |
112 | no matter where |
113 | .I somedir | |
0a216931 MK |
114 | is located in the directory hierarchy. |
115 | This facilitates the creation of "turn-key" applications that | |
116 | do not need to be installed into special directories, | |
117 | but can instead be unpacked into any directory | |
43151de3 | 118 | and still find their own shared objects. |
909df276 MK |
119 | .TP |
120 | .IR $LIB " (or equivalently " ${LIB} ) | |
121 | This expands to | |
122 | .I lib | |
123 | or | |
124 | .I lib64 | |
125 | depending on the architecture | |
126 | (e.g., on x86-64, it expands to | |
127 | .IR lib64 | |
128 | and | |
129 | on x86-32, it expands to | |
130 | .IR lib ). | |
3f2f2461 MK |
131 | .TP |
132 | .IR $PLATFORM " (or equivalently " ${PLATFORM} ) | |
133 | This expands to a string corresponding to the processor type | |
134 | of the host system (e.g., "x86_64"). | |
135 | On some architectures, the Linux kernel doesn't provide a platform | |
136 | string to the dynamic linker. | |
137 | The value of this string is taken from the | |
138 | .BR AT_PLATFORM | |
139 | value in the auxiliary vector (see | |
140 | .BR getauxval (3)). | |
141 | .\" To get an idea of the places that $PLATFORM would match, | |
142 | .\" look at the output of the following: | |
0a216931 | 143 | .\" |
3f2f2461 MK |
144 | .\" mkdir /tmp/d |
145 | .\" LD_LIBRARY_PATH=/tmp/d strace -e open /bin/date 2>&1 | grep /tmp/d | |
0a216931 MK |
146 | .\" |
147 | .\" ld.so lets names be abbreviated, so $O will work for $ORIGIN; | |
148 | .\" Don't do this!! | |
9d4869b3 | 149 | .SH OPTIONS |
fea681da | 150 | .TP |
4d9b6984 | 151 | .B \-\-list |
fea681da MK |
152 | List all dependencies and how they are resolved. |
153 | .TP | |
4d9b6984 | 154 | .B \-\-verify |
fea681da MK |
155 | Verify that program is dynamically linked and this dynamic linker can handle |
156 | it. | |
157 | .TP | |
495dadb7 | 158 | .B \-\-inhibit-cache |
8584e381 MK |
159 | Do not use |
160 | .IR /etc/ld.so.cache . | |
495dadb7 | 161 | .TP |
a831ad17 MK |
162 | .BI \-\-library\-path " path" |
163 | Use | |
164 | .I path | |
165 | instead of | |
fea681da MK |
166 | .B LD_LIBRARY_PATH |
167 | environment variable setting (see below). | |
0a8909c4 MK |
168 | The names |
169 | .IR ORIGIN , | |
170 | .IR LIB , | |
171 | and | |
172 | .IR PLATFORM | |
173 | are interpreted as for the | |
174 | .BR LD_LIBRARY_PATH | |
175 | environment variable. | |
fea681da | 176 | .TP |
a831ad17 MK |
177 | .BI \-\-inhibit\-rpath " list" |
178 | Ignore RPATH and RUNPATH information in object names in | |
179 | .IR list . | |
6e1064d3 | 180 | This option is ignored when running in secure-execution mode (see below). |
608dce1f | 181 | .TP |
a831ad17 MK |
182 | .BI \-\-audit " list" |
183 | Use objects named in | |
184 | .I list | |
185 | as auditors. | |
fea681da | 186 | .SH ENVIRONMENT |
6e1064d3 | 187 | Various environment variables influence the operation of the dynamic linker. |
9894eac3 MK |
188 | .\" |
189 | .SS Secure-execution mode | |
190 | For security reasons, | |
191 | the effects of some environment variables are voided or modified if | |
192 | the dynamic linker determines that the binary should be | |
193 | run in secure-execution mode. | |
59e6b4c6 MK |
194 | (For details, see the discussion of individual environment variables below.) |
195 | A binary is executed in secure-execution mode if the | |
9894eac3 MK |
196 | .B AT_SECURE |
197 | entry in the auxiliary vector (see | |
198 | .BR getauxval (3)) | |
199 | has a nonzero value. | |
200 | This entry may have a nonzero value for various reasons, including: | |
201 | .IP * 3 | |
202 | The process's real and effective user IDs differ, | |
203 | or the real and effective group IDs differ. | |
c93f2202 | 204 | This typically occurs as a result of executing |
9894eac3 MK |
205 | a set-user-ID or set-group-ID program. |
206 | .IP * | |
207 | A process with a non-root user ID executed a binary that | |
208 | conferred permitted or effective capabilities. | |
209 | .IP * | |
210 | A nonzero value may have been set by a Linux Security Module. | |
211 | .\" | |
212 | .SS Environment variables | |
6f6a4840 | 213 | Among the more important environment variables are the following: |
fea681da | 214 | .TP |
9a741b5b | 215 | .BR LD_ASSUME_KERNEL " (since glibc 2.2.3)" |
43151de3 | 216 | Each shared object can inform the dynamic linker of the minimum kernel ABI |
eeb25d47 | 217 | version that it requires. |
ef74d4ad MK |
218 | (This requirement is encoded in an ELF note section that is viewable via |
219 | .IR "readelf\ \-n" | |
220 | as a section labeled | |
221 | .BR NT_GNU_ABI_TAG .) | |
eeb25d47 MK |
222 | At run time, |
223 | the dynamic linker determines the ABI version of the running kernel and | |
43151de3 | 224 | will reject loading shared objects that specify minimum ABI versions |
eeb25d47 MK |
225 | that exceed that ABI version. |
226 | ||
227 | .BR LD_ASSUME_KERNEL | |
228 | can be used to | |
229 | cause the dynamic linker to assume that it is running on a system with | |
230 | a different kernel ABI version. | |
231 | For example, the following command line causes the | |
232 | dynamic linker to assume it is running on Linux 2.2.5 when loading | |
43151de3 | 233 | the shared objects required by |
eeb25d47 MK |
234 | .IR myprog : |
235 | ||
236 | .in +4n | |
237 | .nf | |
238 | $ \fBLD_ASSUME_KERNEL=2.2.5 ./myprog\fP | |
239 | .fi | |
240 | .in | |
241 | ||
43151de3 | 242 | On systems that provide multiple versions of a shared object |
eeb25d47 MK |
243 | (in different directories in the search path) that have |
244 | different minimum kernel ABI version requirements, | |
245 | .BR LD_ASSUME_KERNEL | |
43151de3 | 246 | can be used to select the version of the object that is used |
eeb25d47 MK |
247 | (dependent on the directory search order). |
248 | Historically, the most common use of the | |
8a94e783 | 249 | .BR LD_ASSUME_KERNEL |
eeb25d47 MK |
250 | feature was to manually select the older |
251 | LinuxThreads POSIX threads implementation on systems that provided both | |
252 | LinuxThreads and NPTL | |
260c8fcd MK |
253 | (which latter was typically the default on such systems); |
254 | see | |
255 | .BR pthreads (7). | |
eeb25d47 | 256 | .TP |
9a741b5b | 257 | .BR LD_BIND_NOW " (since glibc 2.1.1)" |
aa796481 | 258 | If set to a nonempty string, |
e1725521 MK |
259 | causes the dynamic linker to resolve all symbols |
260 | at program startup instead of deferring function call resolution to the point | |
261 | when they are first referenced. | |
262 | This is useful when using a debugger. | |
263 | .TP | |
fea681da | 264 | .B LD_LIBRARY_PATH |
75c2bb63 | 265 | A list of directories in which to search for |
fea681da | 266 | ELF libraries at execution-time. |
75c2bb63 | 267 | The items in the list are separated by either colons or semicolons. |
c13182ef | 268 | Similar to the |
fea681da MK |
269 | .B PATH |
270 | environment variable. | |
6e1064d3 | 271 | This variable is ignored in secure-execution mode. |
0a8909c4 MK |
272 | |
273 | Within the pathnames specified in | |
274 | .BR LD_LIBRARY_PATH , | |
99194a09 | 275 | the dynamic linker expands the tokens |
0a8909c4 MK |
276 | .IR $ORIGIN , |
277 | .IR $LIB , | |
278 | and | |
279 | .IR $PLATFORM | |
280 | (or the versions using curly braces around the names) | |
281 | as described above in | |
282 | .IR "Rpath token expansion" . | |
283 | Thus, for example, | |
284 | the following would cause a library to be searched for in either the | |
285 | .I lib | |
286 | or | |
287 | .I lib64 | |
288 | subdirectory below the directory containing the program to be executed: | |
289 | ||
290 | $ \fBLD_LIBRARY_PATH='$ORIGIN/$LIB' prog\fP | |
291 | ||
292 | (Note the use of single quotes, which prevent expansion of | |
99194a09 | 293 | .I $ORIGIN |
0a8909c4 | 294 | and |
99194a09 | 295 | .I $LIB |
0a8909c4 | 296 | as shell variables!) |
fea681da MK |
297 | .TP |
298 | .B LD_PRELOAD | |
df7ef267 | 299 | A list of additional, user-specified, ELF shared |
43151de3 | 300 | objects to be loaded before all others. |
df7ef267 | 301 | The items of the list can be separated by spaces or colons. |
43151de3 MK |
302 | This can be used to selectively override functions in other shared objects. |
303 | The objects are searched for using the rules given under DESCRIPTION. | |
e9a13381 | 304 | |
24fb0923 | 305 | In secure-execution mode, |
eb58a74c | 306 | preload pathnames containing slashes are ignored, |
8e7a186a MK |
307 | and only shared objects in the standard search directories that |
308 | have the set-user-ID mode bit enabled are loaded. | |
0a8909c4 | 309 | |
61c5564c MK |
310 | Within the names specified in the |
311 | .BR LD_PRELOAD | |
99194a09 | 312 | list, the dynamic linker understands the tokens |
0a8909c4 MK |
313 | .IR $ORIGIN , |
314 | .IR $LIB , | |
315 | and | |
316 | .IR $PLATFORM | |
317 | (or the versions using curly braces around the names) | |
318 | as described above in | |
319 | .IR "Rpath token expansion" . | |
320 | .\" Tested with the following: | |
321 | .\" | |
322 | .\" LD_PRELOAD='$LIB/libmod.so' LD_LIBRARY_PATH=. ./prog | |
323 | .\" | |
376c2e1c | 324 | .\" which will preload the libmod.so in 'lib' or 'lib64', using it |
0a8909c4 | 325 | .\" in preference to the version in '.'. |
fea681da | 326 | .TP |
dc4b358f | 327 | .BR LD_TRACE_LOADED_OBJECTS |
01132bd6 | 328 | If set (to any value), causes the program to list its dynamic |
fea681da MK |
329 | dependencies, as if run by |
330 | .BR ldd (1), | |
331 | instead of running normally. | |
332 | .LP | |
333 | Then there are lots of more or less obscure variables, | |
334 | many obsolete or only for internal use. | |
335 | .TP | |
9a741b5b | 336 | .BR LD_AUDIT " (since glibc 2.4)" |
54eb2620 PB |
337 | A colon-separated list of user-specified, ELF shared objects |
338 | to be loaded before all others in a separate linker namespace | |
339 | (i.e., one that does not intrude upon the normal symbol bindings that | |
340 | would occur in the process). | |
43151de3 | 341 | These objects can be used to audit the operation of the dynamic linker. |
54eb2620 | 342 | .B LD_AUDIT |
24fb0923 | 343 | is ignored in secure-execution mode. |
54eb2620 PB |
344 | |
345 | The dynamic linker will notify the audit | |
43151de3 MK |
346 | shared objects at so-called auditing checkpoints\(emfor example, |
347 | loading a new shared object, resolving a symbol, | |
54eb2620 | 348 | or calling a symbol from another shared object\(emby |
43151de3 | 349 | calling an appropriate function within the audit shared object. |
54eb2620 PB |
350 | For details, see |
351 | .BR rtld-audit (7). | |
352 | The auditing interface is largely compatible with that provided on Solaris, | |
353 | as described in its | |
354 | .IR "Linker and Libraries Guide" , | |
355 | in the chapter | |
356 | .IR "Runtime Linker Auditing Interface" . | |
50994c10 | 357 | |
61c5564c MK |
358 | Within the names specified in the |
359 | .BR LD_AUDIT | |
99194a09 | 360 | list, the dynamic linker understands the tokens |
879de6e7 MK |
361 | .IR $ORIGIN , |
362 | .IR $LIB , | |
363 | and | |
364 | .IR $PLATFORM | |
365 | (or the versions using curly braces around the names) | |
366 | as described above in | |
367 | .IR "Rpath token expansion" . | |
368 | ||
50994c10 MK |
369 | Since glibc 2.13, |
370 | .\" commit 8e9f92e9d5d7737afdacf79b76d98c4c42980508 | |
371 | in secure-execution mode, | |
372 | names in the audit list that contain slashes are ignored, | |
373 | and only shared objects in the standard search directories that | |
374 | have the set-user-ID mode bit enabled are loaded. | |
fea681da | 375 | .TP |
9a741b5b | 376 | .BR LD_BIND_NOT " (since glibc 2.1.95)" |
963c1947 MK |
377 | If this environment variable is set to a nonempty string, |
378 | do not update the GOT (global offset table) and PLT (procedure linkage table) | |
a3a72ad2 | 379 | after resolving a function symbol. |
e5e9497f MK |
380 | By combining the use of this variable with |
381 | .BR LD_DEBUG | |
382 | (with the categories | |
383 | .IR bindings | |
384 | and | |
385 | .IR symbols ), | |
386 | one can observe all run-time function bindings. | |
fea681da | 387 | .TP |
9a741b5b | 388 | .BR LD_DEBUG " (since glibc 2.1)" |
fea681da MK |
389 | Output verbose debugging information about the dynamic linker. |
390 | If set to | |
a3fb5696 MK |
391 | .BR all , |
392 | print all debugging information, | |
d81099fb MK |
393 | Setting this variable to |
394 | .BR help | |
395 | does not run the specified program, | |
396 | and displays a help message about which categories can be specified in this | |
fea681da | 397 | environment variable. |
d81099fb MK |
398 | The categories are: |
399 | .RS | |
400 | .TP 12 | |
401 | .I bindings | |
402 | Display information about which definition each symbol is bound to. | |
403 | .TP | |
404 | .I files | |
405 | Display progress for input file. | |
406 | .TP | |
407 | .I libs | |
408 | Display library search paths. | |
409 | .TP | |
410 | .I reloc | |
411 | Display relocation processing. | |
412 | .TP | |
413 | .I scopes | |
414 | Display scope information. | |
415 | .TP | |
416 | .I statistics | |
417 | Display relocation statistics. | |
418 | .TP | |
419 | .I symbols | |
420 | Display search paths for each symbol look-up. | |
421 | .TP | |
422 | .I unused | |
423 | Determine unused DSOs. | |
424 | .TP | |
425 | .I versions | |
426 | Display version dependencies. | |
427 | .RE | |
428 | .IP | |
429 | The value in | |
430 | .BR LD_DEBUG | |
431 | can specify multiple categories, separated by colons, commas, | |
432 | or (if the value is quoted) spaces. | |
433 | ||
e4c14bd9 MK |
434 | Since glibc 2.3.4, |
435 | .B LD_DEBUG | |
ae861bf1 MG |
436 | is ignored in secure-execution mode, unless the file |
437 | .IR /etc/suid\-debug | |
438 | exists (the content of the file is irrelevant). | |
fea681da | 439 | .TP |
9a741b5b | 440 | .BR LD_DEBUG_OUTPUT " (since glibc 2.1)" |
70e26d29 | 441 | File in which |
fea681da | 442 | .B LD_DEBUG |
70e26d29 | 443 | output should be written. |
a3e50dc1 | 444 | The default is standard error. |
097585ed | 445 | .B LD_DEBUG_OUTPUT |
24fb0923 | 446 | is ignored in secure-execution mode. |
fea681da | 447 | .TP |
9a741b5b | 448 | .BR LD_DYNAMIC_WEAK " (since glibc 2.1.91)" |
963c1947 MK |
449 | If this environment variable is defined (with any value), |
450 | allow weak symbols to be overridden (reverting to old glibc behavior). | |
c595ec7e MK |
451 | .\" See weak handling |
452 | .\" https://www.sourceware.org/ml/libc-hacker/2000-06/msg00029.html | |
453 | .\" To: GNU libc hacker <libc-hacker at sourceware dot cygnus dot com> | |
454 | .\" Subject: weak handling | |
455 | .\" From: Ulrich Drepper <drepper at redhat dot com> | |
456 | .\" Date: 07 Jun 2000 20:08:12 -0700 | |
457 | .\" Reply-To: drepper at cygnus dot com (Ulrich Drepper) | |
6e1064d3 | 458 | Since glibc 2.3.4, |
e1725521 | 459 | .B LD_DYNAMIC_WEAK |
24fb0923 | 460 | is ignored in secure-execution mode. |
e1725521 | 461 | .TP |
9a741b5b | 462 | .BR LD_HWCAP_MASK " (since glibc 2.1)" |
e1725521 MK |
463 | Mask for hardware capabilities. |
464 | .TP | |
9a741b5b | 465 | .BR LD_ORIGIN_PATH " (since glibc 2.1)" |
71ffb3ed | 466 | Path where the binary is found. |
24fb0923 | 467 | Since glibc 2.4, |
e1725521 | 468 | .B LD_ORIGIN_PATH |
24fb0923 | 469 | is ignored in secure-execution mode. |
e613d016 | 470 | .\" Used only if $ORIGIN can't be determined by normal means |
e1725521 | 471 | .\" (from the origin path saved at load time, or from /proc/self/exe)? |
7b0cacbb | 472 | .TP |
bdf75f3e | 473 | .BR LD_POINTER_GUARD " (glibc from 2.4 to 2.22)" |
7b0cacbb PB |
474 | Set to 0 to disable pointer guarding. |
475 | Any other value enables pointer guarding, which is also the default. | |
476 | Pointer guarding is a security mechanism whereby some pointers to code | |
477 | stored in writable program memory (return addresses saved by | |
478 | .BR setjmp (3) | |
479 | or function pointers used by various glibc internals) are mangled | |
480 | semi-randomly to make it more difficult for an attacker to hijack | |
481 | the pointers for use in the event of a buffer overrun or | |
482 | stack-smashing attack. | |
ca1c3729 MK |
483 | Since glibc 2.23, |
484 | .\" commit a014cecd82b71b70a6a843e250e06b541ad524f7 | |
485 | .B LD_POINTER_GUARD | |
486 | can no longer be used to disable pointer guarding, | |
487 | which is now always enabled. | |
fea681da | 488 | .TP |
9a741b5b | 489 | .BR LD_PROFILE " (since glibc 2.1)" |
7c7a7df3 | 490 | The name of a (single) shared object to be profiled, |
8a7f3759 | 491 | specified either as a pathname or a soname. |
c64ea262 | 492 | Profiling output is appended to the file whose name is: |
8a7f3759 | 493 | "\fI$LD_PROFILE_OUTPUT\fP/\fI$LD_PROFILE\fP.profile". |
fea681da | 494 | .TP |
9a741b5b | 495 | .BR LD_PROFILE_OUTPUT " (since glibc 2.1)" |
8a7f3759 | 496 | Directory where |
fea681da | 497 | .B LD_PROFILE |
8a7f3759 MK |
498 | output should be written. |
499 | If this variable is not defined, or is defined as an empty string, | |
500 | then the default is | |
501 | .IR /var/tmp . | |
097585ed | 502 | .B LD_PROFILE_OUTPUT |
8977c66c MK |
503 | is ignored in secure-execution mode; instead |
504 | .IR /var/profile | |
505 | is always used. | |
fea681da | 506 | .TP |
9a741b5b | 507 | .BR LD_SHOW_AUXV " (since glibc 2.1)" |
b5ccc9bb MK |
508 | If this environment variable is defined (with any value), |
509 | show the auxiliary array passed up from the kernel (see also | |
510 | .BR getauxval (3)). | |
24fb0923 | 511 | Since glibc 2.3.5, |
ca2bcde1 | 512 | .B LD_SHOW_AUXV |
24fb0923 | 513 | is ignored in secure-execution mode. |
de2a932a | 514 | .TP |
9a741b5b | 515 | .BR LD_TRACE_PRELINKING " (since glibc 2.4)" |
f416bfde | 516 | If this environment variable is defined, |
a5817257 | 517 | trace prelinking of the object whose name is assigned to |
de2a932a MK |
518 | this environment variable. |
519 | (Use | |
520 | .BR ldd (1) | |
521 | to get a list of the objects that might be traced.) | |
522 | If the object name is not recognized, | |
523 | .\" (This is what seems to happen, from experimenting) | |
524 | then all prelinking activity is traced. | |
fea681da | 525 | .TP |
9a741b5b | 526 | .BR LD_USE_LOAD_BIAS " (since glibc 2.3.3)" |
e1725521 MK |
527 | .\" http://sources.redhat.com/ml/libc-hacker/2003-11/msg00127.html |
528 | .\" Subject: [PATCH] Support LD_USE_LOAD_BIAS | |
529 | .\" Jakub Jelinek | |
2656a3fa | 530 | By default (i.e., if this variable is not defined), |
e1725521 | 531 | executables and prelinked |
43151de3 | 532 | shared objects will honor base addresses of their dependent shared objects |
24b74457 | 533 | and (nonprelinked) position-independent executables (PIEs) |
e1725521 MK |
534 | and other shared objects will not honor them. |
535 | If | |
536 | .B LD_USE_LOAD_BIAS | |
dc70d1ea | 537 | is defined with the value 1, both executables and PIEs |
e1725521 MK |
538 | will honor the base addresses. |
539 | If | |
540 | .B LD_USE_LOAD_BIAS | |
541 | is defined with the value 0, | |
542 | neither executables nor PIEs will honor the base addresses. | |
24fb0923 | 543 | This variable is ignored in secure-execution mode. |
fea681da | 544 | .TP |
9a741b5b | 545 | .BR LD_VERBOSE " (since glibc 2.1)" |
aa796481 | 546 | If set to a nonempty string, |
e1725521 | 547 | output symbol versioning information about the |
2216fac7 | 548 | program if the |
e1725521 | 549 | .B LD_TRACE_LOADED_OBJECTS |
2216fac7 | 550 | environment variable has been set. |
fea681da | 551 | .TP |
dc4b358f | 552 | .BR LD_WARN " (since glibc 2.1.3) |
aa796481 | 553 | If set to a nonempty string, warn about unresolved symbols. |
fea681da | 554 | .TP |
9a741b5b | 555 | .BR LD_PREFER_MAP_32BIT_EXEC " (x86-64 only; since glibc 2.23)" |
3cdc1fc4 | 556 | According to the Intel Silvermont software optimization guide, for 64-bit |
5b479f37 L |
557 | applications, branch prediction performance can be negatively impacted |
558 | when the target of a branch is more than 4GB away from the branch. | |
3cdc1fc4 MK |
559 | If this environment variable is set (to any value), |
560 | .BR ld.so | |
561 | will first try to map executable pages using the | |
562 | .BR mmap (2) | |
563 | .BR MAP_32BIT | |
564 | flag, and fall back to mapping without that flag if that attempt fails. | |
81583be9 | 565 | NB: MAP_32BIT will map to the low 2GB (not 4GB) of the address space. |
3cdc1fc4 MK |
566 | Because |
567 | .B MAP_32BIT | |
568 | reduces the address range available for address space layout | |
569 | randomization (ASLR), | |
570 | .B LD_PREFER_MAP_32BIT_EXEC | |
571 | is always disabled in secure-execution mode. | |
fea681da MK |
572 | .SH FILES |
573 | .PD 0 | |
574 | .TP | |
8478ee02 | 575 | .I /lib/ld.so |
fea681da MK |
576 | a.out dynamic linker/loader |
577 | .TP | |
8478ee02 | 578 | .IR /lib/ld\-linux.so. { 1 , 2 } |
fea681da MK |
579 | ELF dynamic linker/loader |
580 | .TP | |
8478ee02 | 581 | .I /etc/ld.so.cache |
fea681da | 582 | File containing a compiled list of directories in which to search for |
43151de3 | 583 | shared objects and an ordered list of candidate shared objects. |
fea681da | 584 | .TP |
8478ee02 | 585 | .I /etc/ld.so.preload |
43151de3 | 586 | File containing a whitespace-separated list of ELF shared objects to |
fea681da | 587 | be loaded before the program. |
fea681da MK |
588 | .TP |
589 | .B lib*.so* | |
43151de3 | 590 | shared objects |
fea681da MK |
591 | .PD |
592 | .SH NOTES | |
8ce45022 | 593 | .SS Hardware capabilities |
43151de3 | 594 | Some shared objects are compiled using hardware-specific instructions which do |
8ce45022 | 595 | not exist on every CPU. |
43151de3 | 596 | Such objects should be installed in directories whose names define the |
8ce45022 MK |
597 | required hardware capabilities, such as |
598 | .IR /usr/lib/sse2/ . | |
599 | The dynamic linker checks these directories against the hardware of the | |
43151de3 | 600 | machine and selects the most suitable version of a given shared object. |
8ce45022 MK |
601 | Hardware capability directories can be cascaded to combine CPU features. |
602 | The list of supported hardware capability names depends on the CPU. | |
603 | The following names are currently recognized: | |
604 | .TP | |
605 | .B Alpha | |
606 | ev4, ev5, ev56, ev6, ev67 | |
607 | .TP | |
608 | .B MIPS | |
609 | loongson2e, loongson2f, octeon, octeon2 | |
610 | .TP | |
611 | .B PowerPC | |
612 | 4xxmac, altivec, arch_2_05, arch_2_06, booke, cellbe, dfp, efpdouble, efpsingle, | |
613 | fpu, ic_snoop, mmu, notb, pa6t, power4, power5, power5+, power6x, ppc32, ppc601, | |
614 | ppc64, smt, spe, ucache, vsx | |
615 | .TP | |
616 | .B SPARC | |
617 | flush, muldiv, stbar, swap, ultra3, v9, v9v, v9v2 | |
618 | .TP | |
619 | .B s390 | |
620 | dfp, eimm, esan3, etf3enh, g5, highgprs, hpage, ldisp, msa, stfle, | |
621 | z900, z990, z9-109, z10, zarch | |
622 | .TP | |
623 | .B x86 (32-bit only) | |
624 | acpi, apic, clflush, cmov, cx8, dts, fxsr, ht, i386, i486, i586, i686, mca, mmx, | |
625 | mtrr, pat, pbe, pge, pn, pse36, sep, ss, sse, sse2, tm | |
fea681da | 626 | .SH SEE ALSO |
6b432477 | 627 | .BR ld (1), |
fea681da | 628 | .BR ldd (1), |
1a7735bb | 629 | .BR pldd (1), |
cf28f98a | 630 | .BR sprof (1), |
639c8860 | 631 | .BR dlopen (3), |
45fa8fcb | 632 | .BR getauxval (3), |
9894eac3 | 633 | .BR capabilities (7), |
c18ecec9 | 634 | .BR rtld-audit (7), |
4d96fe33 MK |
635 | .BR ldconfig (8), |
636 | .BR sln (8) | |
fea681da MK |
637 | .\" .SH AUTHORS |
638 | .\" ld.so: David Engel, Eric Youngdale, Peter MacDonald, Hongjiu Lu, Linus | |
639 | .\" Torvalds, Lars Wirzenius and Mitch D'Souza | |
640 | .\" ld-linux.so: Roland McGrath, Ulrich Drepper and others. | |
641 | .\" | |
642 | .\" In the above, (libc5) stands for David Engel's ld.so/ld-linux.so. |