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1 | Frequently Asked Questions about the GNU C Library | |
2 | ||
3 | This document tries to answer questions a user might have when installing | |
4 | and using glibc. Please make sure you read this before sending questions or | |
5 | bug reports to the maintainers. | |
6 | ||
7 | The GNU C library is very complex. The installation process has not been | |
8 | completely automated; there are too many variables. You can do substantial | |
9 | damage to your system by installing the library incorrectly. Make sure you | |
10 | understand what you are undertaking before you begin. | |
11 | ||
12 | If you have any questions you think should be answered in this document, | |
13 | please let me know. | |
14 | ||
15 | --drepper@cygnus.com | |
16 | \f | |
17 | ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | |
18 | ||
19 | 1. Compiling glibc | |
20 | ||
21 | 1.1. What systems does the GNU C Library run on? | |
22 | 1.2. What compiler do I need to build GNU libc? | |
23 | 1.3. When I try to compile glibc I get only error messages. | |
24 | What's wrong? | |
25 | 1.4. Do I need a special linker or assembler? | |
26 | 1.5. Which compiler should I use for powerpc? | |
27 | 1.6. Which tools should I use for ARM? | |
28 | 1.7. Do I need some more things to compile the GNU C Library? | |
29 | 1.8. What version of the Linux kernel headers should be used? | |
30 | 1.9. The compiler hangs while building iconvdata modules. What's | |
31 | wrong? | |
32 | 1.10. When I run `nm -u libc.so' on the produced library I still | |
33 | find unresolved symbols. Can this be ok? | |
34 | 1.11. What are these `add-ons'? | |
35 | 1.12. My XXX kernel emulates a floating-point coprocessor for me. | |
36 | Should I enable --with-fp? | |
37 | 1.13. When compiling GNU libc I get lots of errors saying functions | |
38 | in glibc are duplicated in libgcc. | |
39 | 1.14. Why do I get messages about missing thread functions when I use | |
40 | librt? I don't even use threads. | |
41 | 1.15. What's the problem with configure --enable-omitfp? | |
42 | 1.16. I get failures during `make check'. What should I do? | |
43 | 1.17. What is symbol versioning good for? Do I need it? | |
44 | 1.18. How can I compile on my fast ix86 machine a working libc for my slow | |
45 | i386? After installing libc, programs abort with "Illegal | |
46 | Instruction". | |
47 | ||
48 | 2. Installation and configuration issues | |
49 | ||
50 | 2.1. Can I replace the libc on my Linux system with GNU libc? | |
51 | 2.2. How do I configure GNU libc so that the essential libraries | |
52 | like libc.so go into /lib and the other into /usr/lib? | |
53 | 2.3. How should I avoid damaging my system when I install GNU libc? | |
54 | 2.4. Do I need to use GNU CC to compile programs that will use the | |
55 | GNU C Library? | |
56 | 2.5. When linking with the new libc I get unresolved symbols | |
57 | `crypt' and `setkey'. Why aren't these functions in the | |
58 | libc anymore? | |
59 | 2.6. When I use GNU libc on my Linux system by linking against | |
60 | the libc.so which comes with glibc all I get is a core dump. | |
61 | 2.7. Looking through the shared libc file I haven't found the | |
62 | functions `stat', `lstat', `fstat', and `mknod' and while | |
63 | linking on my Linux system I get error messages. How is | |
64 | this supposed to work? | |
65 | 2.8. When I run an executable on one system which I compiled on | |
66 | another, I get dynamic linker errors. Both systems have the same | |
67 | version of glibc installed. What's wrong? | |
68 | 2.9. How can I compile gcc 2.7.2.1 from the gcc source code using | |
69 | glibc 2.x? | |
70 | 2.10. The `gencat' utility cannot process the catalog sources which | |
71 | were used on my Linux libc5 based system. Why? | |
72 | 2.11. Programs using libc have their messages translated, but other | |
73 | behavior is not localized (e.g. collating order); why? | |
74 | 2.12. I have set up /etc/nis.conf, and the Linux libc 5 with NYS | |
75 | works great. But the glibc NIS+ doesn't seem to work. | |
76 | 2.13. I have killed ypbind to stop using NIS, but glibc | |
77 | continues using NIS. | |
78 | 2.14. Under Linux/Alpha, I always get "do_ypcall: clnt_call: | |
79 | RPC: Unable to receive; errno = Connection refused" when using NIS. | |
80 | 2.15. After installing glibc name resolving doesn't work properly. | |
81 | 2.16. How do I create the databases for NSS? | |
82 | 2.17. I have /usr/include/net and /usr/include/scsi as symlinks | |
83 | into my Linux source tree. Is that wrong? | |
84 | 2.18. Programs like `logname', `top', `uptime' `users', `w' and | |
85 | `who', show incorrect information about the (number of) | |
86 | users on my system. Why? | |
87 | 2.19. After upgrading to glibc 2.1 with symbol versioning I get | |
88 | errors about undefined symbols. What went wrong? | |
89 | 2.20. When I start the program XXX after upgrading the library | |
90 | I get | |
91 | XXX: Symbol `_sys_errlist' has different size in shared | |
92 | object, consider re-linking | |
93 | Why? What should I do? | |
94 | 2.21. What do I need for C++ development? | |
95 | 2.22. Even statically linked programs need some shared libraries | |
96 | which is not acceptable for me. What can I do? | |
97 | 2.23. I just upgraded my Linux system to glibc and now I get | |
98 | errors whenever I try to link any program. | |
99 | 2.24. When I use nscd the machine freezes. | |
100 | 2.25. I need lots of open files. What do I have to do? | |
101 | 2.26. How do I get the same behavior on parsing /etc/passwd and | |
102 | /etc/group as I have with libc5 ? | |
103 | 2.27. What needs to be recompiled when upgrading from glibc 2.0 to glibc | |
104 | 2.1? | |
105 | 2.28. Why is extracting files via tar so slow? | |
106 | 2.29. Compiling programs I get parse errors in libio.h (e.g. "parse error | |
107 | before `_IO_seekoff'"). How should I fix this? | |
108 | 2.30. After upgrading to glibc 2.1, libraries that were compiled against | |
109 | glibc 2.0.x don't work anymore. | |
110 | 2.31. What happened to the Berkeley DB libraries? Can I still use db | |
111 | in /etc/nsswitch.conf? | |
112 | ||
113 | 3. Source and binary incompatibilities, and what to do about them | |
114 | ||
115 | 3.1. I expect GNU libc to be 100% source code compatible with | |
116 | the old Linux based GNU libc. Why isn't it like this? | |
117 | 3.2. Why does getlogin() always return NULL on my Linux box? | |
118 | 3.3. Where are the DST_* constants found in <sys/time.h> on many | |
119 | systems? | |
120 | 3.4. The prototypes for `connect', `accept', `getsockopt', | |
121 | `setsockopt', `getsockname', `getpeername', `send', | |
122 | `sendto', and `recvfrom' are different in GNU libc from | |
123 | any other system I saw. This is a bug, isn't it? | |
124 | 3.5. On Linux I've got problems with the declarations in Linux | |
125 | kernel headers. | |
126 | 3.6. I don't include any kernel headers myself but the compiler | |
127 | still complains about redeclarations of types in the kernel | |
128 | headers. | |
129 | 3.7. Why don't signals interrupt system calls anymore? | |
130 | 3.8. I've got errors compiling code that uses certain string | |
131 | functions. Why? | |
132 | 3.9. I get compiler messages "Initializer element not constant" with | |
133 | stdin/stdout/stderr. Why? | |
134 | 3.10. I can't compile with gcc -traditional (or | |
135 | -traditional-cpp). Why? | |
136 | 3.11. I get some errors with `gcc -ansi'. Isn't glibc ANSI compatible? | |
137 | 3.12. I can't access some functions anymore. nm shows that they do | |
138 | exist but linking fails nevertheless. | |
139 | 3.13. When using the db-2 library which comes with glibc is used in | |
140 | the Perl db modules the testsuite is not passed. This did not | |
141 | happen with db-1, gdbm, or ndbm. | |
142 | ||
143 | Removed. Does not apply anymore. | |
144 | 3.14. The pow() inline function I get when including <math.h> is broken. | |
145 | I get segmentation faults when I run the program. | |
146 | 3.15. The sys/sem.h file lacks the definition of `union semun'. | |
147 | 3.16. Why has <netinet/ip_fw.h> disappeared? | |
148 | 3.17. I get floods of warnings when I use -Wconversion and include | |
149 | <string.h> or <math.h>. | |
150 | 3.18. After upgrading to glibc 2.1, I receive errors about | |
151 | unresolved symbols, like `_dl_initial_searchlist' and can not | |
152 | execute any binaries. What went wrong? | |
153 | 3.19. bonnie reports that char i/o with glibc 2 is much slower than with | |
154 | libc5. What can be done? | |
155 | 3.20. Programs compiled with glibc 2.1 can't read db files made with glibc | |
156 | 2.0. What has changed that programs like rpm break? | |
157 | ||
158 | Removed. Does not apply anymore. | |
159 | 3.21. Autoconf's AC_CHECK_FUNC macro reports that a function exists, but | |
160 | when I try to use it, it always returns -1 and sets errno to ENOSYS. | |
161 | 3.22. My program segfaults when I call fclose() on the FILE* returned | |
162 | from setmntent(). Is this a glibc bug? | |
163 | ||
164 | 4. Miscellaneous | |
165 | ||
166 | 4.1. After I changed configure.in I get `Autoconf version X.Y. | |
167 | or higher is required for this script'. What can I do? | |
168 | 4.2. When I try to compile code which uses IPv6 headers and | |
169 | definitions on my Linux 2.x.y system I am in trouble. | |
170 | Nothing seems to work. | |
171 | 4.3. When I set the timezone by setting the TZ environment variable | |
172 | to EST5EDT things go wrong since glibc computes the wrong time | |
173 | from this information. | |
174 | 4.4. What other sources of documentation about glibc are available? | |
175 | 4.5. The timezone string for Sydney/Australia is wrong since even when | |
176 | daylight saving time is in effect the timezone string is EST. | |
177 | 4.6. I've build make 3.77 against glibc 2.1 and now make gets | |
178 | segmentation faults. | |
179 | 4.7. Why do so many programs using math functions fail on my AlphaStation? | |
180 | 4.8. The conversion table for character set XX does not match with | |
181 | what I expect. | |
182 | ||
183 | \f | |
184 | ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | |
185 | ||
186 | 1. Compiling glibc | |
187 | ||
188 | 1.1. What systems does the GNU C Library run on? | |
189 | ||
190 | {UD} This is difficult to answer. The file `README' lists the architectures | |
191 | GNU libc was known to run on *at some time*. This does not mean that it | |
192 | still can be compiled and run on them now. | |
193 | ||
194 | The systems glibc is known to work on as of this release, and most probably | |
195 | in the future, are: | |
196 | ||
197 | *-*-gnu GNU Hurd | |
198 | i[3456]86-*-linux-gnu Linux-2.x on Intel | |
199 | m68k-*-linux-gnu Linux-2.x on Motorola 680x0 | |
200 | alpha-*-linux-gnu Linux-2.x on DEC Alpha | |
201 | powerpc-*-linux-gnu Linux and MkLinux on PowerPC systems | |
202 | sparc-*-linux-gnu Linux-2.x on SPARC | |
203 | sparc64-*-linux-gnu Linux-2.x on UltraSPARC | |
204 | arm-*-none ARM standalone systems | |
205 | arm-*-linux Linux-2.x on ARM | |
206 | arm-*-linuxaout Linux-2.x on ARM using a.out binaries | |
207 | ||
208 | Ports to other Linux platforms are in development, and may in fact work | |
209 | already, but no one has sent us success reports for them. Currently no | |
210 | ports to other operating systems are underway, although a few people have | |
211 | expressed interest. | |
212 | ||
213 | If you have a system not listed above (or in the `README' file) and you are | |
214 | really interested in porting it, contact | |
215 | ||
216 | <bug-glibc@gnu.org> | |
217 | ||
218 | ||
219 | 1.2. What compiler do I need to build GNU libc? | |
220 | ||
221 | {UD} You must use GNU CC to compile GNU libc. A lot of extensions of GNU CC | |
222 | are used to increase portability and speed. | |
223 | ||
224 | GNU CC is found, like all other GNU packages, on | |
225 | ||
226 | ftp://ftp.gnu.org/pub/gnu | |
227 | ||
228 | and the many mirror sites. ftp.gnu.org is always overloaded, so try to find | |
229 | a local mirror first. | |
230 | ||
231 | You should always try to use the latest official release. Older versions | |
232 | may not have all the features GNU libc requires. The current releases of | |
233 | egcs (1.0.3 and 1.1.1) should work with the GNU C library (for powerpc see | |
234 | question 1.5; for ARM see question 1.6). | |
235 | ||
236 | While the GNU CC should be able to compile glibc it is nevertheless adviced | |
237 | to use EGCS. Comparing the sizes of glibc on Intel compiled with a recent | |
238 | EGCS and gcc 2.8.1 shows this: | |
239 | ||
240 | text data bss dec hex filename | |
241 | egcs-2.93.10 862897 15944 12824 891665 d9b11 libc.so | |
242 | gcc-2.8.1 959965 16468 12152 988585 f15a9 libc.so | |
243 | ||
244 | Make up your own decision. | |
245 | ||
246 | GNU CC versions 2.95 and above are derived from egcs, and they may do even | |
247 | better. | |
248 | ||
249 | Please note that gcc 2.95 and 2.95.x cannot compile glibc on Alpha due to | |
250 | problems in the complex float support. | |
251 | ||
252 | ||
253 | 1.3. When I try to compile glibc I get only error messages. | |
254 | What's wrong? | |
255 | ||
256 | {UD} You definitely need GNU make to build GNU libc. No other make | |
257 | program has the needed functionality. | |
258 | ||
259 | We recommend version GNU make version 3.75 or 3.77. Versions before 3.75 | |
260 | have bugs and/or are missing features. Version 3.76 has bugs which | |
261 | appear when building big projects like GNU libc. 3.76.1 appears to work but | |
262 | some people have reported problems. If you build GNU make 3.77 from source, | |
263 | please read question 4.6 first. | |
264 | ||
265 | ||
266 | 1.4. Do I need a special linker or assembler? | |
267 | ||
268 | {ZW} If you want a shared library, you need a linker and assembler that | |
269 | understand all the features of ELF, including weak and versioned symbols. | |
270 | The static library can be compiled with less featureful tools, but lacks key | |
271 | features such as NSS. | |
272 | ||
273 | For Linux or Hurd, you want binutils 2.8.1.0.23, 2.9.1, or 2.9.1.0.15 or | |
274 | higher. These are the only versions we've tested and found reliable. Other | |
275 | versions after 2.8.1.0.23 may work but we don't recommend them, especially | |
276 | not when C++ is involved. Earlier versions do not work at all. | |
277 | ||
278 | Other operating systems may come with system tools that have all the | |
279 | necessary features, but this is moot because glibc hasn't been ported to | |
280 | them. | |
281 | ||
282 | ||
283 | 1.5. Which compiler should I use for powerpc? | |
284 | ||
285 | {GK} You want to use at least gcc 2.95 (together with the right versions | |
286 | of all the other tools, of course). See also question question 2.8. | |
287 | ||
288 | ||
289 | 1.6. Which tools should I use for ARM? | |
290 | ||
291 | {PB} You should use egcs 1.1 or a later version. For ELF systems some | |
292 | changes are needed to the compiler; a patch against egcs-1.1.x can be found | |
293 | at: | |
294 | ||
295 | <ftp://ftp.netwinder.org/users/p/philb/egcs-1.1.1pre2-diff-981126> | |
296 | ||
297 | Binutils 2.9.1.0.16 or later is also required. | |
298 | ||
299 | ||
300 | 1.7. Do I need some more things to compile the GNU C Library? | |
301 | ||
302 | {UD} Yes, there are some more :-). | |
303 | ||
304 | * GNU gettext. This package contains the tools needed to construct | |
305 | `message catalog' files containing translated versions of system | |
306 | messages. See ftp://ftp.gnu.org/pub/gnu or better any mirror | |
307 | site. (We distribute compiled message catalogs, but they may not be | |
308 | updated in patches.) Please note that the required minimal version | |
309 | (0.10.35) of gettext is alpha software and available from | |
310 | ftp://alpha.gnu.org/gnu . | |
311 | ||
312 | * Some files are built with special tools. E.g., files ending in .gperf | |
313 | need a `gperf' program. The GNU version (now available in a separate | |
314 | package, formerly only as part of libg++) is known to work while some | |
315 | vendor versions do not. | |
316 | ||
317 | You should not need these tools unless you change the source files. | |
318 | ||
319 | * Perl 5 is needed if you wish to test an installation of GNU libc | |
320 | as the primary C library. | |
321 | ||
322 | * When compiling for Linux, the header files of the Linux kernel must | |
323 | be available to the compiler as <linux/*.h> and <asm/*.h>. | |
324 | ||
325 | * lots of disk space (~400MB for i?86-linux; more for RISC platforms). | |
326 | ||
327 | * plenty of time. Compiling just the shared and static libraries for | |
328 | i?86-linux takes approximately 1h on an AMD-K6@225MHz w/ 96MB of RAM, | |
329 | 45mins on a Celeron@400MHz w/ 128MB, and 55mins on a Alpha@533MHz w/ 256MB. | |
330 | Multiply this by 1.5 or 2.0 if you build profiling and/or the highly | |
331 | optimized version as well. For Hurd systems times are much higher. | |
332 | ||
333 | You should avoid compiling in a NFS mounted filesystem. This is | |
334 | very slow. | |
335 | ||
336 | James Troup <J.J.Troup@comp.brad.ac.uk> reports a compile time of | |
337 | 45h34m for a full build (shared, static, and profiled) on Atari | |
338 | Falcon (Motorola 68030 @ 16 Mhz, 14 Mb memory) and Jan Barte | |
339 | <yann@plato.uni-paderborn.de> reports 22h48m on Atari TT030 | |
340 | (Motorola 68030 @ 32 Mhz, 34 Mb memory) | |
341 | ||
342 | A full build of the PowerPC library took 1h on a PowerPC 750@400Mhz w/ | |
343 | 64MB of RAM, and about 9h on a 601@60Mhz w/ 72Mb. | |
344 | ||
345 | If you have some more measurements let me know. | |
346 | ||
347 | ||
348 | 1.8. What version of the Linux kernel headers should be used? | |
349 | ||
350 | {AJ,UD} The headers from the most recent Linux kernel should be used. The | |
351 | headers used while compiling the GNU C library and the kernel binary used | |
352 | when using the library do not need to match. The GNU C library runs without | |
353 | problems on kernels that are older than the kernel headers used. The other | |
354 | way round (compiling the GNU C library with old kernel headers and running | |
355 | on a recent kernel) does not necessarily work. For example you can't use | |
356 | new kernel features if you used old kernel headers to compile the GNU C | |
357 | library. | |
358 | ||
359 | {ZW} Even if you are using a 2.0 kernel on your machine, we recommend you | |
360 | compile GNU libc with 2.2 kernel headers. That way you won't have to | |
361 | recompile libc if you ever upgrade to kernel 2.2. To tell libc which | |
362 | headers to use, give configure the --with-headers switch | |
363 | (e.g. --with-headers=/usr/src/linux-2.2.0/include). | |
364 | ||
365 | Note that you must configure the 2.2 kernel if you do this, otherwise libc | |
366 | will be unable to find <linux/version.h>. Just change the current directory | |
367 | to the root of the 2.2 tree and do `make include/linux/version.h'. | |
368 | ||
369 | ||
370 | 1.9. The compiler hangs while building iconvdata modules. What's | |
371 | wrong? | |
372 | ||
373 | {ZW} This is a problem with old versions of GCC. Initialization of large | |
374 | static arrays is very slow. The compiler will eventually finish; give it | |
375 | time. | |
376 | ||
377 | The problem is fixed in egcs 1.1. | |
378 | ||
379 | ||
380 | 1.10. When I run `nm -u libc.so' on the produced library I still | |
381 | find unresolved symbols. Can this be ok? | |
382 | ||
383 | {UD} Yes, this is ok. There can be several kinds of unresolved symbols: | |
384 | ||
385 | * magic symbols automatically generated by the linker. These have names | |
386 | like __start_* and __stop_* | |
387 | ||
388 | * symbols starting with _dl_* come from the dynamic linker | |
389 | ||
390 | * weak symbols, which need not be resolved at all (fabs for example) | |
391 | ||
392 | Generally, you should make sure you find a real program which produces | |
393 | errors while linking before deciding there is a problem. | |
394 | ||
395 | ||
396 | 1.11. What are these `add-ons'? | |
397 | ||
398 | {UD} To avoid complications with export rules or external source code some | |
399 | optional parts of the libc are distributed as separate packages (e.g., the | |
400 | crypt package, see question 2.5). | |
401 | ||
402 | To use these packages as part of GNU libc, just unpack the tarfiles in the | |
403 | libc source directory and tell the configuration script about them using the | |
404 | --enable-add-ons option. If you give just --enable-add-ons configure tries | |
405 | to find all the add-on packages in your source tree. This may not work. If | |
406 | it doesn't, or if you want to select only a subset of the add-ons, give a | |
407 | comma-separated list of the add-ons to enable: | |
408 | ||
409 | configure --enable-add-ons=crypt,linuxthreads | |
410 | ||
411 | for example. | |
412 | ||
413 | Add-ons can add features (including entirely new shared libraries), override | |
414 | files, provide support for additional architectures, and just about anything | |
415 | else. The existing makefiles do most of the work; only some few stub rules | |
416 | must be written to get everything running. | |
417 | ||
418 | Most add-ons are tightly coupled to a specific GNU libc version. Please | |
419 | check that the add-ons work with the GNU libc. For example the crypt and | |
420 | linuxthreads add-ons have the same numbering scheme as the libc and will in | |
421 | general only work with the corresponding libc. | |
422 | ||
423 | ||
424 | 1.12. My XXX kernel emulates a floating-point coprocessor for me. | |
425 | Should I enable --with-fp? | |
426 | ||
427 | {ZW} An emulated FPU is just as good as a real one, as far as the C library | |
428 | is concerned. You only need to say --without-fp if your machine has no way | |
429 | to execute floating-point instructions. | |
430 | ||
431 | People who are interested in squeezing the last drop of performance | |
432 | out of their machine may wish to avoid the trap overhead, but this is | |
433 | far more trouble than it's worth: you then have to compile | |
434 | *everything* this way, including the compiler's internal libraries | |
435 | (libgcc.a for GNU C), because the calling conventions change. | |
436 | ||
437 | ||
438 | 1.13. When compiling GNU libc I get lots of errors saying functions | |
439 | in glibc are duplicated in libgcc. | |
440 | ||
441 | {EY} This is *exactly* the same problem that I was having. The problem was | |
442 | due to the fact that configure didn't correctly detect that the linker flag | |
443 | --no-whole-archive was supported in my linker. In my case it was because I | |
444 | had run ./configure with bogus CFLAGS, and the test failed. | |
445 | ||
446 | One thing that is particularly annoying about this problem is that once this | |
447 | is misdetected, running configure again won't fix it unless you first delete | |
448 | config.cache. | |
449 | ||
450 | {UD} Starting with glibc-2.0.3 there should be a better test to avoid some | |
451 | problems of this kind. The setting of CFLAGS is checked at the very | |
452 | beginning and if it is not usable `configure' will bark. | |
453 | ||
454 | ||
455 | 1.14. Why do I get messages about missing thread functions when I use | |
456 | librt? I don't even use threads. | |
457 | ||
458 | {UD} In this case you probably mixed up your installation. librt uses | |
459 | threads internally and has implicit references to the thread library. | |
460 | Normally these references are satisfied automatically but if the thread | |
461 | library is not in the expected place you must tell the linker where it is. | |
462 | When using GNU ld it works like this: | |
463 | ||
464 | gcc -o foo foo.c -Wl,-rpath-link=/some/other/dir -lrt | |
465 | ||
466 | The `/some/other/dir' should contain the thread library. `ld' will use the | |
467 | given path to find the implicitly referenced library while not disturbing | |
468 | any other link path. | |
469 | ||
470 | ||
471 | 1.15. What's the problem with configure --enable-omitfp? | |
472 | ||
473 | {AJ} When --enable-omitfp is set the libraries are built without frame | |
474 | pointers. Some compilers produce buggy code for this model and therefore we | |
475 | don't advise using it at the moment. | |
476 | ||
477 | If you use --enable-omitfp, you're on your own. If you encounter problems | |
478 | with a library that was build this way, we advise you to rebuild the library | |
479 | without --enable-omitfp. If the problem vanishes consider tracking the | |
480 | problem down and report it as compiler failure. | |
481 | ||
482 | Since a library built with --enable-omitfp is undebuggable on most systems, | |
483 | debuggable libraries are also built - you can use them by appending "_g" to | |
484 | the library names. | |
485 | ||
486 | The compilation of these extra libraries and the compiler optimizations slow | |
487 | down the build process and need more disk space. | |
488 | ||
489 | ||
490 | 1.16. I get failures during `make check'. What should I do? | |
491 | ||
492 | {AJ} The testsuite should compile and run cleanly on your system; every | |
493 | failure should be looked into. Depending on the failures, you probably | |
494 | should not install the library at all. | |
495 | ||
496 | You should consider using the `glibcbug' script to report the failure, | |
497 | providing as much detail as possible. If you run a test directly, please | |
498 | remember to set up the environment correctly. You want to test the compiled | |
499 | library - and not your installed one. The best way is to copy the exact | |
500 | command line which failed and run the test from the subdirectory for this | |
501 | test in the sources. | |
502 | ||
503 | There are some failures which are not directly related to the GNU libc: | |
504 | - Some compilers produce buggy code. No compiler gets single precision | |
505 | complex numbers correct on Alpha. Otherwise, the egcs 1.1 release should be | |
506 | ok; gcc 2.8.1 might cause some failures; gcc 2.7.2.x is so buggy that | |
507 | explicit checks have been used so that you can't build with it. | |
508 | - The kernel might have bugs. For example on Linux/Alpha 2.0.34 the | |
509 | floating point handling has quite a number of bugs and therefore most of | |
510 | the test cases in the math subdirectory will fail. Linux 2.2 has | |
511 | fixes for the floating point support on Alpha. The Linux/SPARC kernel has | |
512 | also some bugs in the FPU emulation code (as of Linux 2.2.0). | |
513 | - Other tools might have problems. For example bash 2.03 gives a | |
514 | segmentation fault running the tst-rpmatch.sh test script. | |
515 | ||
516 | ||
517 | 1.17. What is symbol versioning good for? Do I need it? | |
518 | ||
519 | {AJ} Symbol versioning solves problems that are related to interface | |
520 | changes. One version of an interface might have been introduced in a | |
521 | previous version of the GNU C library but the interface or the semantics of | |
522 | the function has been changed in the meantime. For binary compatibility | |
523 | with the old library, a newer library needs to still have the old interface | |
524 | for old programs. On the other hand, new programs should use the new | |
525 | interface. Symbol versioning is the solution for this problem. The GNU | |
526 | libc version 2.1 uses symbol versioning by default if the installed binutils | |
527 | supports it. | |
528 | ||
529 | We don't advise building without symbol versioning, since you lose binary | |
530 | compatibility - forever! The binary compatibility you lose is not only | |
531 | against the previous version of the GNU libc (version 2.0) but also against | |
532 | all future versions. | |
533 | ||
534 | ||
535 | 1.18. How can I compile on my fast ix86 machine a working libc for my slow | |
536 | i386? After installing libc, programs abort with "Illegal | |
537 | Instruction". | |
538 | ||
539 | {AJ} glibc and gcc might generate some instructions on your machine that | |
540 | aren't available on i386. You've got to tell glibc that you're configuring | |
541 | for i386 with adding i386 as your machine, for example: | |
542 | ||
543 | ../configure --prefix=/usr i386-pc-linux-gnu | |
544 | ||
545 | And you need to tell gcc to only generate i386 code, just add `-mcpu=i386' | |
546 | (just -m386 doesn't work) to your CFLAGS. | |
547 | ||
548 | {UD} This applies not only to the i386. Compiling on a i686 for any older | |
549 | model will also fail if the above methods are not used. | |
550 | ||
551 | \f | |
552 | . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . | |
553 | ||
554 | 2. Installation and configuration issues | |
555 | ||
556 | 2.1. Can I replace the libc on my Linux system with GNU libc? | |
557 | ||
558 | {UD} You cannot replace any existing libc for Linux with GNU libc. It is | |
559 | binary incompatible and therefore has a different major version. You can, | |
560 | however, install it alongside your existing libc. | |
561 | ||
562 | For Linux there are three major libc versions: | |
563 | libc-4 a.out libc | |
564 | libc-5 original ELF libc | |
565 | libc-6 GNU libc | |
566 | ||
567 | You can have any combination of these three installed. For more information | |
568 | consult documentation for shared library handling. The Makefiles of GNU | |
569 | libc will automatically generate the needed symbolic links which the linker | |
570 | will use. | |
571 | ||
572 | ||
573 | 2.2. How do I configure GNU libc so that the essential libraries | |
574 | like libc.so go into /lib and the other into /usr/lib? | |
575 | ||
576 | {UD,AJ} Like all other GNU packages GNU libc is designed to use a base | |
577 | directory and install all files relative to this. The default is | |
578 | /usr/local, because this is safe (it will not damage the system if installed | |
579 | there). If you wish to install GNU libc as the primary C library on your | |
580 | system, set the base directory to /usr (i.e. run configure --prefix=/usr | |
581 | <other_options>). Note that this can damage your system; see question 2.3 for | |
582 | details. | |
583 | ||
584 | Some systems like Linux have a filesystem standard which makes a difference | |
585 | between essential libraries and others. Essential libraries are placed in | |
586 | /lib because this directory is required to be located on the same disk | |
587 | partition as /. The /usr subtree might be found on another | |
588 | partition/disk. If you configure for Linux with --prefix=/usr, then this | |
589 | will be done automatically. | |
590 | ||
591 | To install the essential libraries which come with GNU libc in /lib on | |
592 | systems other than Linux one must explicitly request it. Autoconf has no | |
593 | option for this so you have to use a `configparms' file (see the `INSTALL' | |
594 | file for details). It should contain: | |
595 | ||
596 | slibdir=/lib | |
597 | sysconfdir=/etc | |
598 | ||
599 | The first line specifies the directory for the essential libraries, the | |
600 | second line the directory for system configuration files. | |
601 | ||
602 | ||
603 | 2.3. How should I avoid damaging my system when I install GNU libc? | |
604 | ||
605 | {ZW} If you wish to be cautious, do not configure with --prefix=/usr. If | |
606 | you don't specify a prefix, glibc will be installed in /usr/local, where it | |
607 | will probably not break anything. (If you wish to be certain, set the | |
608 | prefix to something like /usr/local/glibc2 which is not used for anything.) | |
609 | ||
610 | The dangers when installing glibc in /usr are twofold: | |
611 | ||
612 | * glibc will overwrite the headers in /usr/include. Other C libraries | |
613 | install a different but overlapping set of headers there, so the effect | |
614 | will probably be that you can't compile anything. You need to rename | |
615 | /usr/include out of the way before running `make install'. (Do not throw | |
616 | it away; you will then lose the ability to compile programs against your | |
617 | old libc.) | |
618 | ||
619 | * None of your old libraries, static or shared, can be used with a | |
620 | different C library major version. For shared libraries this is not a | |
621 | problem, because the filenames are different and the dynamic linker | |
622 | will enforce the restriction. But static libraries have no version | |
623 | information. You have to evacuate all the static libraries in | |
624 | /usr/lib to a safe location. | |
625 | ||
626 | The situation is rather similar to the move from a.out to ELF which | |
627 | long-time Linux users will remember. | |
628 | ||
629 | ||
630 | 2.4. Do I need to use GNU CC to compile programs that will use the | |
631 | GNU C Library? | |
632 | ||
633 | {ZW} In theory, no; the linker does not care, and the headers are supposed | |
634 | to check for GNU CC before using its extensions to the C language. | |
635 | ||
636 | However, there are currently no ports of glibc to systems where another | |
637 | compiler is the default, so no one has tested the headers extensively | |
638 | against another compiler. You may therefore encounter difficulties. If you | |
639 | do, please report them as bugs. | |
640 | ||
641 | Also, in several places GNU extensions provide large benefits in code | |
642 | quality. For example, the library has hand-optimized, inline assembly | |
643 | versions of some string functions. These can only be used with GCC. See | |
644 | question 3.8 for details. | |
645 | ||
646 | ||
647 | 2.5. When linking with the new libc I get unresolved symbols | |
648 | `crypt' and `setkey'. Why aren't these functions in the | |
649 | libc anymore? | |
650 | ||
651 | {UD} The US places restrictions on exporting cryptographic programs and | |
652 | source code. Until this law gets abolished we cannot ship the cryptographic | |
653 | functions together with glibc. | |
654 | ||
655 | The functions are available, as an add-on (see question 1.11). People in the US | |
656 | may get it from the same place they got GNU libc from. People outside the | |
657 | US should get the code from ftp.gwdg.de [134.76.11.100] in the directory | |
658 | pub/linux/glibc, or another archive site outside the USA. The README explains | |
659 | how to install the sources. | |
660 | ||
661 | If you already have the crypt code on your system the reason for the failure | |
662 | is probably that you did not link with -lcrypt. The crypto functions are in | |
663 | a separate library to make it possible to export GNU libc binaries from the | |
664 | US. | |
665 | ||
666 | ||
667 | 2.6. When I use GNU libc on my Linux system by linking against | |
668 | the libc.so which comes with glibc all I get is a core dump. | |
669 | ||
670 | {UD} On Linux, gcc sets the dynamic linker to /lib/ld-linux.so.1 unless the | |
671 | user specifies a --dynamic-linker argument. This is the name of the libc5 | |
672 | dynamic linker, which does not work with glibc. | |
673 | ||
674 | For casual use of GNU libc you can just specify to the linker | |
675 | --dynamic-linker=/lib/ld-linux.so.2 | |
676 | ||
677 | which is the glibc dynamic linker, on Linux systems. On other systems the | |
678 | name is /lib/ld.so.1. When linking via gcc, you've got to add | |
679 | -Wl,--dynamic-linker=/lib/ld-linux.so.2 | |
680 | ||
681 | to the gcc command line. | |
682 | ||
683 | To change your environment to use GNU libc for compiling you need to change | |
684 | the `specs' file of your gcc. This file is normally found at | |
685 | ||
686 | /usr/lib/gcc-lib/<arch>/<version>/specs | |
687 | ||
688 | In this file you have to change a few things: | |
689 | ||
690 | - change `ld-linux.so.1' to `ld-linux.so.2' | |
691 | ||
692 | - remove all expression `%{...:-lgmon}'; there is no libgmon in glibc | |
693 | ||
694 | - fix a minor bug by changing %{pipe:-} to %| | |
695 | ||
696 | Here is what the gcc-2.7.2 specs file should look like when GNU libc is | |
697 | installed at /usr: | |
698 | ||
699 | ----------------------------------------------------------------------- | |
700 | *asm: | |
701 | %{V} %{v:%{!V:-V}} %{Qy:} %{!Qn:-Qy} %{n} %{T} %{Ym,*} %{Yd,*} %{Wa,*:%*} | |
702 | ||
703 | *asm_final: | |
704 | %| | |
705 | ||
706 | *cpp: | |
707 | %{fPIC:-D__PIC__ -D__pic__} %{fpic:-D__PIC__ -D__pic__} %{!m386:-D__i486__} %{posix:-D_POSIX_SOURCE} %{pthread:-D_REENTRANT} | |
708 | ||
709 | *cc1: | |
710 | %{profile:-p} | |
711 | ||
712 | *cc1plus: | |
713 | ||
714 | ||
715 | *endfile: | |
716 | %{!shared:crtend.o%s} %{shared:crtendS.o%s} crtn.o%s | |
717 | ||
718 | *link: | |
719 | -m elf_i386 %{shared:-shared} %{!shared: %{!ibcs: %{!static: %{rdynamic:-export-dynamic} %{!dynamic-linker:-dynamic-linker /lib/ld-linux.so.2}} %{static:-static}}} | |
720 | ||
721 | *lib: | |
722 | %{!shared: %{pthread:-lpthread} %{profile:-lc_p} %{!profile: -lc}} | |
723 | ||
724 | *libgcc: | |
725 | -lgcc | |
726 | ||
727 | *startfile: | |
728 | %{!shared: %{pg:gcrt1.o%s} %{!pg:%{p:gcrt1.o%s} %{!p:%{profile:gcrt1.o%s} %{!profile:crt1.o%s}}}} crti.o%s %{!shared:crtbegin.o%s} %{shared:crtbeginS.o%s} | |
729 | ||
730 | *switches_need_spaces: | |
731 | ||
732 | ||
733 | *signed_char: | |
734 | %{funsigned-char:-D__CHAR_UNSIGNED__} | |
735 | ||
736 | *predefines: | |
737 | -D__ELF__ -Dunix -Di386 -Dlinux -Asystem(unix) -Asystem(posix) -Acpu(i386) -Amachine(i386) | |
738 | ||
739 | *cross_compile: | |
740 | 0 | |
741 | ||
742 | *multilib: | |
743 | . ; | |
744 | ||
745 | ----------------------------------------------------------------------- | |
746 | ||
747 | Things get a bit more complicated if you have GNU libc installed in some | |
748 | other place than /usr, i.e., if you do not want to use it instead of the old | |
749 | libc. In this case the needed startup files and libraries are not found in | |
750 | the regular places. So the specs file must tell the compiler and linker | |
751 | exactly what to use. | |
752 | ||
753 | Version 2.7.2.3 does and future versions of GCC will automatically | |
754 | provide the correct specs. | |
755 | ||
756 | ||
757 | 2.7. Looking through the shared libc file I haven't found the | |
758 | functions `stat', `lstat', `fstat', and `mknod' and while | |
759 | linking on my Linux system I get error messages. How is | |
760 | this supposed to work? | |
761 | ||
762 | {RM} Believe it or not, stat and lstat (and fstat, and mknod) are supposed | |
763 | to be undefined references in libc.so.6! Your problem is probably a missing | |
764 | or incorrect /usr/lib/libc.so file; note that this is a small text file now, | |
765 | not a symlink to libc.so.6. It should look something like this: | |
766 | ||
767 | GROUP ( libc.so.6 libc_nonshared.a ) | |
768 | ||
769 | ||
770 | 2.8. When I run an executable on one system which I compiled on | |
771 | another, I get dynamic linker errors. Both systems have the same | |
772 | version of glibc installed. What's wrong? | |
773 | ||
774 | {ZW} Glibc on one of these systems was compiled with gcc 2.7 or 2.8, the | |
775 | other with egcs (any version). Egcs has functions in its internal | |
776 | `libgcc.a' to support exception handling with C++. They are linked into | |
777 | any program or dynamic library compiled with egcs, whether it needs them or | |
778 | not. Dynamic libraries then turn around and export those functions again | |
779 | unless special steps are taken to prevent them. | |
780 | ||
781 | When you link your program, it resolves its references to the exception | |
782 | functions to the ones exported accidentally by libc.so. That works fine as | |
783 | long as libc has those functions. On the other system, libc doesn't have | |
784 | those functions because it was compiled by gcc 2.8, and you get undefined | |
785 | symbol errors. The symbols in question are named things like | |
786 | `__register_frame_info'. | |
787 | ||
788 | For glibc 2.0, the workaround is to not compile libc with egcs. We've also | |
789 | incorporated a patch which should prevent the EH functions sneaking into | |
790 | libc. It doesn't matter what compiler you use to compile your program. | |
791 | ||
792 | For glibc 2.1, we've chosen to do it the other way around: libc.so | |
793 | explicitly provides the EH functions. This is to prevent other shared | |
794 | libraries from doing it. | |
795 | ||
796 | {UD} Starting with glibc 2.1.1 you can compile glibc with gcc 2.8.1 or | |
797 | newer since we have explicitly add references to the functions causing the | |
798 | problem. But you nevertheless should use EGCS for other reasons | |
799 | (see question 1.2). | |
800 | ||
801 | {GK} On some Linux distributions for PowerPC, you can see this when you have | |
802 | built gcc or egcs from the Web sources (gcc versions 2.95 or earlier), then | |
803 | re-built glibc. This happens because in these versions of gcc, exception | |
804 | handling is implemented using an older method; the people making the | |
805 | distributions are a little ahead of their time. | |
806 | ||
807 | A quick solution to this is to find the libgcc.a file that came with the | |
808 | distribution (it would have been installed under /usr/lib/gcc-lib), do | |
809 | `ar x libgcc.a frame.o' to get the frame.o file out, and add a line saying | |
810 | `LDLIBS-c.so += frame.o' to the file `configparms' in the directory you're | |
811 | building in. You can check you've got the right `frame.o' file by running | |
812 | `nm frame.o' and checking that it has the symbols defined that you're | |
813 | missing. | |
814 | ||
815 | This will let you build glibc with the C compiler. The C++ compiler | |
816 | will still be binary incompatible with any C++ shared libraries that | |
817 | you got with your distribution. | |
818 | ||
819 | ||
820 | 2.9. How can I compile gcc 2.7.2.1 from the gcc source code using | |
821 | glibc 2.x? | |
822 | ||
823 | {AJ} There's only correct support for glibc 2.0.x in gcc 2.7.2.3 or later. | |
824 | But you should get at least gcc 2.8.1 or egcs 1.1 (or later versions) | |
825 | instead. | |
826 | ||
827 | ||
828 | 2.10. The `gencat' utility cannot process the catalog sources which | |
829 | were used on my Linux libc5 based system. Why? | |
830 | ||
831 | {UD} The `gencat' utility provided with glibc complies to the XPG standard. | |
832 | The older Linux version did not obey the standard, so they are not | |
833 | compatible. | |
834 | ||
835 | To ease the transition from the Linux version some of the non-standard | |
836 | features are also present in the `gencat' program of GNU libc. This mainly | |
837 | includes the use of symbols for the message number and the automatic | |
838 | generation of header files which contain the needed #defines to map the | |
839 | symbols to integers. | |
840 | ||
841 | Here is a simple SED script to convert at least some Linux specific catalog | |
842 | files to the XPG4 form: | |
843 | ||
844 | ----------------------------------------------------------------------- | |
845 | # Change catalog source in Linux specific format to standard XPG format. | |
846 | # Ulrich Drepper <drepper@cygnus.com>, 1996. | |
847 | # | |
848 | /^\$ #/ { | |
849 | h | |
850 | s/\$ #\([^ ]*\).*/\1/ | |
851 | x | |
852 | s/\$ #[^ ]* *\(.*\)/\$ \1/ | |
853 | } | |
854 | ||
855 | /^# / { | |
856 | s/^# \(.*\)/\1/ | |
857 | G | |
858 | s/\(.*\)\n\(.*\)/\2 \1/ | |
859 | } | |
860 | ----------------------------------------------------------------------- | |
861 | ||
862 | ||
863 | 2.11. Programs using libc have their messages translated, but other | |
864 | behavior is not localized (e.g. collating order); why? | |
865 | ||
866 | {ZW} Translated messages are automatically installed, but the locale | |
867 | database that controls other behaviors is not. You need to run localedef to | |
868 | install this database, after you have run `make install'. For example, to | |
869 | set up the French Canadian locale, simply issue the command | |
870 | ||
871 | localedef -i fr_CA -f ISO-8859-1 fr_CA | |
872 | ||
873 | Please see localedata/README in the source tree for further details. | |
874 | ||
875 | ||
876 | 2.12. I have set up /etc/nis.conf, and the Linux libc 5 with NYS | |
877 | works great. But the glibc NIS+ doesn't seem to work. | |
878 | ||
879 | {TK} The glibc NIS+ implementation uses a /var/nis/NIS_COLD_START file for | |
880 | storing information about the NIS+ server and their public keys, because the | |
881 | nis.conf file does not contain all the necessary information. You have to | |
882 | copy a NIS_COLD_START file from a Solaris client (the NIS_COLD_START file is | |
883 | byte order independent) or generate it with nisinit from the nis-tools | |
884 | package; available at | |
885 | ||
886 | http://www.suse.de/~kukuk/linux/nisplus.html | |
887 | ||
888 | ||
889 | 2.13. I have killed ypbind to stop using NIS, but glibc | |
890 | continues using NIS. | |
891 | ||
892 | {TK} For faster NIS lookups, glibc uses the /var/yp/binding/ files from | |
893 | ypbind. ypbind 3.3 and older versions don't always remove these files, so | |
894 | glibc will continue to use them. Other BSD versions seem to work correctly. | |
895 | Until ypbind 3.4 is released, you can find a patch at | |
896 | ||
897 | <ftp://ftp.kernel.org/pub/linux/utils/net/NIS/ypbind-3.3-glibc4.diff.gz> | |
898 | ||
899 | ||
900 | 2.14. Under Linux/Alpha, I always get "do_ypcall: clnt_call: | |
901 | RPC: Unable to receive; errno = Connection refused" when using NIS. | |
902 | ||
903 | {TK} You need a ypbind version which is 64bit clean. Some versions are not | |
904 | 64bit clean. A 64bit clean implementation is ypbind-mt. For ypbind 3.3, | |
905 | you need the patch from ftp.kernel.org (See the previous question). I don't | |
906 | know about other versions. | |
907 | ||
908 | ||
909 | 2.15. After installing glibc name resolving doesn't work properly. | |
910 | ||
911 | {AJ} You probably should read the manual section describing nsswitch.conf | |
912 | (just type `info libc "NSS Configuration File"'). The NSS configuration | |
913 | file is usually the culprit. | |
914 | ||
915 | ||
916 | 2.16. How do I create the databases for NSS? | |
917 | ||
918 | {AJ} If you have an entry "db" in /etc/nsswitch.conf you should also create | |
919 | the database files. The glibc sources contain a Makefile which does the | |
920 | necessary conversion and calls to create those files. The file is | |
921 | `db-Makefile' in the subdirectory `nss' and you can call it with `make -f | |
922 | db-Makefile'. Please note that not all services are capable of using a | |
923 | database. Currently passwd, group, ethers, protocol, rpc, services shadow | |
924 | and netgroup are implemented. See also question question 2.31. | |
925 | ||
926 | ||
927 | 2.17. I have /usr/include/net and /usr/include/scsi as symlinks | |
928 | into my Linux source tree. Is that wrong? | |
929 | ||
930 | {PB} This was necessary for libc5, but is not correct when using glibc. | |
931 | Including the kernel header files directly in user programs usually does not | |
932 | work (see question 3.5). glibc provides its own <net/*> and <scsi/*> header | |
933 | files to replace them, and you may have to remove any symlink that you have | |
934 | in place before you install glibc. However, /usr/include/asm and | |
935 | /usr/include/linux should remain as they were. | |
936 | ||
937 | ||
938 | 2.18. Programs like `logname', `top', `uptime' `users', `w' and | |
939 | `who', show incorrect information about the (number of) | |
940 | users on my system. Why? | |
941 | ||
942 | {MK} See question 3.2. | |
943 | ||
944 | ||
945 | 2.19. After upgrading to glibc 2.1 with symbol versioning I get | |
946 | errors about undefined symbols. What went wrong? | |
947 | ||
948 | {AJ} The problem is caused either by wrong program code or tools. In the | |
949 | versioned libc a lot of symbols are now local that were global symbols in | |
950 | previous versions. It seems that programs linked against older versions | |
951 | often accidentally used libc global variables -- something that should not | |
952 | happen. | |
953 | ||
954 | The only way to fix this is to recompile your program. Sorry, that's the | |
955 | price you might have to pay once for quite a number of advantages with | |
956 | symbol versioning. | |
957 | ||
958 | ||
959 | 2.20. When I start the program XXX after upgrading the library | |
960 | I get | |
961 | XXX: Symbol `_sys_errlist' has different size in shared | |
962 | object, consider re-linking | |
963 | Why? What should I do? | |
964 | ||
965 | {UD} As the message says, relink the binary. The problem is that a few | |
966 | symbols from the library can change in size and there is no way to avoid | |
967 | this. _sys_errlist is a good example. Occasionally there are new error | |
968 | numbers added to the kernel and this must be reflected at user level, | |
969 | breaking programs that refer to them directly. | |
970 | ||
971 | Such symbols should normally not be used at all. There are mechanisms to | |
972 | avoid using them. In the case of _sys_errlist, there is the strerror() | |
973 | function which should _always_ be used instead. So the correct fix is to | |
974 | rewrite that part of the application. | |
975 | ||
976 | In some situations (especially when testing a new library release) it might | |
977 | be possible that a symbol changed size when that should not have happened. | |
978 | So in case of doubt report such a warning message as a problem. | |
979 | ||
980 | ||
981 | 2.21. What do I need for C++ development? | |
982 | ||
983 | {HJ,AJ} You need either egcs 1.1 which comes directly with libstdc++ or | |
984 | gcc-2.8.1 together with libstdc++ 2.8.1.1. egcs 1.1 has the better C++ | |
985 | support and works directly with glibc 2.1. If you use gcc-2.8.1 with | |
986 | libstdc++ 2.8.1.1, you need to modify libstdc++ a bit. A patch is available | |
987 | as: | |
988 | <ftp://alpha.gnu.org/gnu/libstdc++-2.8.1.1-glibc2.1-diff.gz> | |
989 | ||
990 | Please note that libg++ 2.7.2 (and the Linux Versions 2.7.2.x) doesn't work | |
991 | very well with the GNU C library due to vtable thunks. If you're upgrading | |
992 | from glibc 2.0.x to 2.1 you have to recompile libstdc++ since the library | |
993 | compiled for 2.0 is not compatible due to the new Large File Support (LFS) | |
994 | in version 2.1. | |
995 | ||
996 | {UD} But since in the case of a shared libstdc++ the version numbers should | |
997 | be different existing programs will continue to work. | |
998 | ||
999 | ||
1000 | 2.22. Even statically linked programs need some shared libraries | |
1001 | which is not acceptable for me. What can I do? | |
1002 | ||
1003 | {AJ} NSS (for details just type `info libc "Name Service Switch"') won't | |
1004 | work properly without shared libraries. NSS allows using different services | |
1005 | (e.g. NIS, files, db, hesiod) by just changing one configuration file | |
1006 | (/etc/nsswitch.conf) without relinking any programs. The only disadvantage | |
1007 | is that now static libraries need to access shared libraries. This is | |
1008 | handled transparently by the GNU C library. | |
1009 | ||
1010 | A solution is to configure glibc with --enable-static-nss. In this case you | |
1011 | can create a static binary that will use only the services dns and files | |
1012 | (change /etc/nsswitch.conf for this). You need to link explicitly against | |
1013 | all these services. For example: | |
1014 | ||
1015 | gcc -static test-netdb.c -o test-netdb.c \ | |
1016 | -lc -lnss_files -lnss_dns -lresolv | |
1017 | ||
1018 | The problem with this approach is that you've got to link every static | |
1019 | program that uses NSS routines with all those libraries. | |
1020 | ||
1021 | {UD} In fact, one cannot say anymore that a libc compiled with this | |
1022 | option is using NSS. There is no switch anymore. Therefore it is | |
1023 | *highly* recommended *not* to use --enable-static-nss since this makes | |
1024 | the behaviour of the programs on the system inconsistent. | |
1025 | ||
1026 | ||
1027 | 2.23. I just upgraded my Linux system to glibc and now I get | |
1028 | errors whenever I try to link any program. | |
1029 | ||
1030 | {ZW} This happens when you have installed glibc as the primary C library but | |
1031 | have stray symbolic links pointing at your old C library. If the first | |
1032 | `libc.so' the linker finds is libc 5, it will use that. Your program | |
1033 | expects to be linked with glibc, so the link fails. | |
1034 | ||
1035 | The most common case is that glibc put its `libc.so' in /usr/lib, but there | |
1036 | was a `libc.so' from libc 5 in /lib, which gets searched first. To fix the | |
1037 | problem, just delete /lib/libc.so. You may also need to delete other | |
1038 | symbolic links in /lib, such as /lib/libm.so if it points to libm.so.5. | |
1039 | ||
1040 | {AJ} The perl script test-installation.pl which is run as last step during | |
1041 | an installation of glibc that is configured with --prefix=/usr should help | |
1042 | detect these situations. If the script reports problems, something is | |
1043 | really screwed up. | |
1044 | ||
1045 | ||
1046 | 2.24. When I use nscd the machine freezes. | |
1047 | ||
1048 | {UD} You cannot use nscd with Linux 2.0.*. There is functionality missing | |
1049 | in the kernel and work-arounds are not suitable. Besides, some parts of the | |
1050 | kernel are too buggy when it comes to using threads. | |
1051 | ||
1052 | If you need nscd, you have to use at least a 2.1 kernel. | |
1053 | ||
1054 | Note that I have at this point no information about any other platform. | |
1055 | ||
1056 | ||
1057 | 2.25. I need lots of open files. What do I have to do? | |
1058 | ||
1059 | {AJ} This is at first a kernel issue. The kernel defines limits with | |
1060 | OPEN_MAX the number of simultaneous open files and with FD_SETSIZE the | |
1061 | number of used file descriptors. You need to change these values in your | |
1062 | kernel and recompile the kernel so that the kernel allows to use more open | |
1063 | files. You don't necessarily need to recompile the GNU C library since the | |
1064 | only place where OPEN_MAX and FD_SETSIZE is really needed in the library | |
1065 | itself is the size of fd_set which is used by select. | |
1066 | ||
1067 | The GNU C library is now select free. This means it internally has no | |
1068 | limits imposed by the `fd_set' type. Instead all places where the | |
1069 | functionality is needed the `poll' function is used. | |
1070 | ||
1071 | If you increase the number of file descriptors in the kernel you don't need | |
1072 | to recompile the C library. | |
1073 | ||
1074 | {UD} You can always get the maximum number of file descriptors a process is | |
1075 | allowed to have open at any time using | |
1076 | ||
1077 | number = sysconf (_SC_OPEN_MAX); | |
1078 | ||
1079 | This will work even if the kernel limits change. | |
1080 | ||
1081 | ||
1082 | 2.26. How do I get the same behavior on parsing /etc/passwd and | |
1083 | /etc/group as I have with libc5 ? | |
1084 | ||
1085 | {TK} The name switch setup in /etc/nsswitch.conf selected by most Linux | |
1086 | distributions does not support +/- and netgroup entries in the files like | |
1087 | /etc/passwd. Though this is the preferred setup some people might have | |
1088 | setups coming over from the libc5 days where it was the default to recognize | |
1089 | lines like this. To get back to the old behaviour one simply has to change | |
1090 | the rules for passwd, group, and shadow in the nsswitch.conf file as | |
1091 | follows: | |
1092 | ||
1093 | passwd: compat | |
1094 | group: compat | |
1095 | shadow: compat | |
1096 | ||
1097 | passwd_compat: nis | |
1098 | group_compat: nis | |
1099 | shadow_compat: nis | |
1100 | ||
1101 | ||
1102 | 2.27. What needs to be recompiled when upgrading from glibc 2.0 to glibc | |
1103 | 2.1? | |
1104 | ||
1105 | {AJ,CG} If you just upgrade the glibc from 2.0.x (x <= 7) to 2.1, binaries | |
1106 | that have been linked against glibc 2.0 will continue to work. | |
1107 | ||
1108 | If you compile your own binaries against glibc 2.1, you also need to | |
1109 | recompile some other libraries. The problem is that libio had to be changed | |
1110 | and therefore libraries that are based or depend on the libio of glibc, | |
1111 | e.g. ncurses, slang and most C++ libraries, need to be recompiled. If you | |
1112 | experience strange segmentation faults in your programs linked against glibc | |
1113 | 2.1, you might need to recompile your libraries. | |
1114 | ||
1115 | Another problem is that older binaries that were linked statically against | |
1116 | glibc 2.0 will reference the older nss modules (libnss_files.so.1 instead of | |
1117 | libnss_files.so.2), so don't remove them. Also, the old glibc-2.0 compiled | |
1118 | static libraries (libfoo.a) which happen to depend on the older libio | |
1119 | behavior will be broken by the glibc 2.1 upgrade. We plan to produce a | |
1120 | compatibility library that people will be able to link in if they want | |
1121 | to compile a static library generated against glibc 2.0 into a program | |
1122 | on a glibc 2.1 system. You just add -lcompat and you should be fine. | |
1123 | ||
1124 | The glibc-compat add-on will provide the libcompat.a library, the older | |
1125 | nss modules, and a few other files. Together, they should make it | |
1126 | possible to do development with old static libraries on a glibc 2.1 | |
1127 | system. This add-on is still in development. You can get it from | |
1128 | <ftp://alpha.gnu.org/gnu/glibc/glibc-compat-2.1.tar.gz> | |
1129 | but please keep in mind that it is experimental. | |
1130 | ||
1131 | ||
1132 | 2.28. Why is extracting files via tar so slow? | |
1133 | ||
1134 | {AJ} Extracting of tar archives might be quite slow since tar has to look up | |
1135 | userid and groupids and doesn't cache negative results. If you have nis or | |
1136 | nisplus in your /etc/nsswitch.conf for the passwd and/or group database, | |
1137 | each file extractions needs a network connection. There are two possible | |
1138 | solutions: | |
1139 | ||
1140 | - do you really need NIS/NIS+ (some Linux distributions add by default | |
1141 | nis/nisplus even if it's not needed)? If not, just remove the entries. | |
1142 | ||
1143 | - if you need NIS/NIS+, use the Name Service Cache Daemon nscd that comes | |
1144 | with glibc 2.1. | |
1145 | ||
1146 | ||
1147 | 2.29. Compiling programs I get parse errors in libio.h (e.g. "parse error | |
1148 | before `_IO_seekoff'"). How should I fix this? | |
1149 | ||
1150 | {AJ} You might get the following errors when upgrading to glibc 2.1: | |
1151 | ||
1152 | In file included from /usr/include/stdio.h:57, | |
1153 | from ... | |
1154 | /usr/include/libio.h:335: parse error before `_IO_seekoff' | |
1155 | /usr/include/libio.h:335: parse error before `_G_off64_t' | |
1156 | /usr/include/libio.h:336: parse error before `_IO_seekpos' | |
1157 | /usr/include/libio.h:336: parse error before `_G_fpos64_t' | |
1158 | ||
1159 | The problem is a wrong _G_config.h file in your include path. The | |
1160 | _G_config.h file that comes with glibc 2.1 should be used and not one from | |
1161 | libc5 or from a compiler directory. To check which _G_config.h file the | |
1162 | compiler uses, compile your program with `gcc -E ...|grep G_config.h' and | |
1163 | remove that file. Your compiler should pick up the file that has been | |
1164 | installed by glibc 2.1 in your include directory. | |
1165 | ||
1166 | ||
1167 | 2.30. After upgrading to glibc 2.1, libraries that were compiled against | |
1168 | glibc 2.0.x don't work anymore. | |
1169 | ||
1170 | {AJ} See question 2.27. | |
1171 | ||
1172 | ||
1173 | 2.31. What happened to the Berkeley DB libraries? Can I still use db | |
1174 | in /etc/nsswitch.conf? | |
1175 | ||
1176 | {AJ} Due to too many incompatible changes in disk layout and API of Berkeley | |
1177 | DB and a too tight coupling of libc and libdb, the db library has been | |
1178 | removed completely from glibc 2.2. The only place that really used the | |
1179 | Berkeley DB was the NSS db module. | |
1180 | ||
1181 | The NSS db module has been rewritten to support a number of different | |
1182 | versions of Berkeley DB for the NSS db module. Currently the releases 2.x | |
1183 | and 3.x of Berkeley DB are supported. The older db 1.85 library is not | |
1184 | supported. You can use the version from glibc 2.1.x or download a version | |
1185 | from Sleepycat Software (http://www.sleepycat.com). The library has to be | |
1186 | compiled as shared library and installed in the system lib directory | |
1187 | (normally /lib). The library needs to have a special soname to be found by | |
1188 | the NSS module. | |
1189 | ||
1190 | If public structures change in a new Berkeley db release, this needs to be | |
1191 | reflected in glibc. | |
1192 | ||
1193 | Currently the code searches for libraries with a soname of "libdb.so.3" | |
1194 | (that's the name from db 2.4.14 which comes with glibc 2.1.x) and | |
1195 | "libdb-3.0.so" (the name used by db 3.0.55 as default). | |
1196 | ||
1197 | \f | |
1198 | . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . | |
1199 | ||
1200 | 3. Source and binary incompatibilities, and what to do about them | |
1201 | ||
1202 | 3.1. I expect GNU libc to be 100% source code compatible with | |
1203 | the old Linux based GNU libc. Why isn't it like this? | |
1204 | ||
1205 | {DMT,UD} Not every extension in Linux libc's history was well thought-out. | |
1206 | In fact it had a lot of problems with standards compliance and with | |
1207 | cleanliness. With the introduction of a new version number these errors can | |
1208 | now be corrected. Here is a list of the known source code | |
1209 | incompatibilities: | |
1210 | ||
1211 | * _GNU_SOURCE: glibc does not make the GNU extensions available | |
1212 | automatically. If a program depends on GNU extensions or some | |
1213 | other non-standard functionality, it is necessary to compile it | |
1214 | with the C compiler option -D_GNU_SOURCE, or better, to put | |
1215 | `#define _GNU_SOURCE' at the beginning of your source files, before | |
1216 | any C library header files are included. This difference normally | |
1217 | manifests itself in the form of missing prototypes and/or data type | |
1218 | definitions. Thus, if you get such errors, the first thing you | |
1219 | should do is try defining _GNU_SOURCE and see if that makes the | |
1220 | problem go away. | |
1221 | ||
1222 | For more information consult the file `NOTES' in the GNU C library | |
1223 | sources. | |
1224 | ||
1225 | * reboot(): GNU libc sanitizes the interface of reboot() to be more | |
1226 | compatible with the interface used on other OSes. reboot() as | |
1227 | implemented in glibc takes just one argument. This argument | |
1228 | corresponds to the third argument of the Linux reboot system call. | |
1229 | That is, a call of the form reboot(a, b, c) needs to be changed into | |
1230 | reboot(c). Beside this the header <sys/reboot.h> defines the needed | |
1231 | constants for the argument. These RB_* constants should be used | |
1232 | instead of the cryptic magic numbers. | |
1233 | ||
1234 | * swapon(): the interface of this function didn't change, but the | |
1235 | prototype is in a separate header file <sys/swap.h>. This header | |
1236 | file also provides the SWAP_* constants defined by <linux/swap.h>; | |
1237 | you should use them for the second argument to swapon(). | |
1238 | ||
1239 | * errno: If a program uses the variable "errno", then it _must_ | |
1240 | include <errno.h>. The old libc often (erroneously) declared this | |
1241 | variable implicitly as a side-effect of including other libc header | |
1242 | files. glibc is careful to avoid such namespace pollution, which, | |
1243 | in turn, means that you really need to include the header files that | |
1244 | you depend on. This difference normally manifests itself in the | |
1245 | form of the compiler complaining about references to an undeclared | |
1246 | symbol "errno". | |
1247 | ||
1248 | * Linux-specific syscalls: All Linux system calls now have appropriate | |
1249 | library wrappers and corresponding declarations in various header files. | |
1250 | This is because the syscall() macro that was traditionally used to | |
1251 | work around missing syscall wrappers are inherently non-portable and | |
1252 | error-prone. The following table lists all the new syscall stubs, | |
1253 | the header-file declaring their interface and the system call name. | |
1254 | ||
1255 | syscall name: wrapper name: declaring header file: | |
1256 | ------------- ------------- ---------------------- | |
1257 | bdflush bdflush <sys/kdaemon.h> | |
1258 | syslog ksyslog_ctl <sys/klog.h> | |
1259 | ||
1260 | * lpd: Older versions of lpd depend on a routine called _validuser(). | |
1261 | The library does not provide this function, but instead provides | |
1262 | __ivaliduser() which has a slightly different interface. Simply | |
1263 | upgrading to a newer lpd should fix this problem (e.g., the 4.4BSD | |
1264 | lpd is known to be working). | |
1265 | ||
1266 | * resolver functions/BIND: like on many other systems the functions of | |
1267 | the resolver library are not included in libc itself. There is a | |
1268 | separate library libresolv. If you get undefined symbol errors for | |
1269 | symbols starting with `res_*' simply add -lresolv to your linker | |
1270 | command line. | |
1271 | ||
1272 | * the `signal' function's behavior corresponds to the BSD semantic and | |
1273 | not the SysV semantic as it was in libc-5. The interface on all GNU | |
1274 | systems shall be the same and BSD is the semantic of choice. To use | |
1275 | the SysV behavior simply use `sysv_signal', or define _XOPEN_SOURCE. | |
1276 | See question 3.7 for details. | |
1277 | ||
1278 | ||
1279 | 3.2. Why does getlogin() always return NULL on my Linux box? | |
1280 | ||
1281 | {UD} The GNU C library has a format for the UTMP and WTMP file which differs | |
1282 | from what your system currently has. It was extended to fulfill the needs | |
1283 | of the next years when IPv6 is introduced. The record size is different and | |
1284 | some fields have different positions. The files written by functions from | |
1285 | the one library cannot be read by functions from the other library. Sorry, | |
1286 | but this is what a major release is for. It's better to have a cut now than | |
1287 | having no means to support the new techniques later. | |
1288 | ||
1289 | {MK} There is however a (partial) solution for this problem. Please take a | |
1290 | look at the file `login/README.utmpd'. | |
1291 | ||
1292 | ||
1293 | 3.3. Where are the DST_* constants found in <sys/time.h> on many | |
1294 | systems? | |
1295 | ||
1296 | {UD} These constants come from the old BSD days and are not used anymore | |
1297 | (libc5 does not actually implement the handling although the constants are | |
1298 | defined). | |
1299 | ||
1300 | Instead GNU libc contains zone database support and compatibility code for | |
1301 | POSIX TZ environment variable handling. For former is very much preferred | |
1302 | (see question 4.3). | |
1303 | ||
1304 | ||
1305 | 3.4. The prototypes for `connect', `accept', `getsockopt', | |
1306 | `setsockopt', `getsockname', `getpeername', `send', | |
1307 | `sendto', and `recvfrom' are different in GNU libc from | |
1308 | any other system I saw. This is a bug, isn't it? | |
1309 | ||
1310 | {UD} No, this is no bug. This version of GNU libc already follows the new | |
1311 | Single Unix specifications (and I think the POSIX.1g draft which adopted the | |
1312 | solution). The type for a parameter describing a size is now `socklen_t', a | |
1313 | new type. | |
1314 | ||
1315 | ||
1316 | 3.5. On Linux I've got problems with the declarations in Linux | |
1317 | kernel headers. | |
1318 | ||
1319 | {UD,AJ} On Linux, the use of kernel headers is reduced to the minimum. This | |
1320 | gives Linus the ability to change the headers more freely. Also, user | |
1321 | programs are now insulated from changes in the size of kernel data | |
1322 | structures. | |
1323 | ||
1324 | For example, the sigset_t type is 32 or 64 bits wide in the kernel. In | |
1325 | glibc it is 1024 bits wide. This guarantees that when the kernel gets a | |
1326 | bigger sigset_t (for POSIX.1e realtime support, say) user programs will not | |
1327 | have to be recompiled. Consult the header files for more information about | |
1328 | the changes. | |
1329 | ||
1330 | Therefore you shouldn't include Linux kernel header files directly if glibc | |
1331 | has defined a replacement. Otherwise you might get undefined results because | |
1332 | of type conflicts. | |
1333 | ||
1334 | ||
1335 | 3.6. I don't include any kernel headers myself but the compiler | |
1336 | still complains about redeclarations of types in the kernel | |
1337 | headers. | |
1338 | ||
1339 | {UD} The kernel headers before Linux 2.1.61 and 2.0.32 don't work correctly | |
1340 | with glibc. Compiling C programs is possible in most cases but C++ programs | |
1341 | have (due to the change of the name lookups for `struct's) problems. One | |
1342 | prominent example is `struct fd_set'. | |
1343 | ||
1344 | There might be some problems left but 2.1.61/2.0.32 fix most of the known | |
1345 | ones. See the BUGS file for other known problems. | |
1346 | ||
1347 | ||
1348 | 3.7. Why don't signals interrupt system calls anymore? | |
1349 | ||
1350 | {ZW} By default GNU libc uses the BSD semantics for signal(), unlike Linux | |
1351 | libc 5 which used System V semantics. This is partially for compatibility | |
1352 | with other systems and partially because the BSD semantics tend to make | |
1353 | programming with signals easier. | |
1354 | ||
1355 | There are three differences: | |
1356 | ||
1357 | * BSD-style signals that occur in the middle of a system call do not | |
1358 | affect the system call; System V signals cause the system call to | |
1359 | fail and set errno to EINTR. | |
1360 | ||
1361 | * BSD signal handlers remain installed once triggered. System V signal | |
1362 | handlers work only once, so one must reinstall them each time. | |
1363 | ||
1364 | * A BSD signal is blocked during the execution of its handler. In other | |
1365 | words, a handler for SIGCHLD (for example) does not need to worry about | |
1366 | being interrupted by another SIGCHLD. It may, however, be interrupted | |
1367 | by other signals. | |
1368 | ||
1369 | There is general consensus that for `casual' programming with signals, the | |
1370 | BSD semantics are preferable. You don't need to worry about system calls | |
1371 | returning EINTR, and you don't need to worry about the race conditions | |
1372 | associated with one-shot signal handlers. | |
1373 | ||
1374 | If you are porting an old program that relies on the old semantics, you can | |
1375 | quickly fix the problem by changing signal() to sysv_signal() throughout. | |
1376 | Alternatively, define _XOPEN_SOURCE before including <signal.h>. | |
1377 | ||
1378 | For new programs, the sigaction() function allows you to specify precisely | |
1379 | how you want your signals to behave. All three differences listed above are | |
1380 | individually switchable on a per-signal basis with this function. | |
1381 | ||
1382 | If all you want is for one specific signal to cause system calls to fail and | |
1383 | return EINTR (for example, to implement a timeout) you can do this with | |
1384 | siginterrupt(). | |
1385 | ||
1386 | ||
1387 | 3.8. I've got errors compiling code that uses certain string | |
1388 | functions. Why? | |
1389 | ||
1390 | {AJ} glibc 2.1 has special string functions that are faster than the normal | |
1391 | library functions. Some of the functions are additionally implemented as | |
1392 | inline functions and others as macros. This might lead to problems with | |
1393 | existing codes but it is explicitly allowed by ISO C. | |
1394 | ||
1395 | The optimized string functions are only used when compiling with | |
1396 | optimizations (-O1 or higher). The behavior can be changed with two feature | |
1397 | macros: | |
1398 | ||
1399 | * __NO_STRING_INLINES: Don't do any string optimizations. | |
1400 | * __USE_STRING_INLINES: Use assembly language inline functions (might | |
1401 | increase code size dramatically). | |
1402 | ||
1403 | Since some of these string functions are now additionally defined as macros, | |
1404 | code like "char *strncpy();" doesn't work anymore (and is unnecessary, since | |
1405 | <string.h> has the necessary declarations). Either change your code or | |
1406 | define __NO_STRING_INLINES. | |
1407 | ||
1408 | {UD} Another problem in this area is that gcc still has problems on machines | |
1409 | with very few registers (e.g., ix86). The inline assembler code can require | |
1410 | almost all the registers and the register allocator cannot always handle | |
1411 | this situation. | |
1412 | ||
1413 | One can disable the string optimizations selectively. Instead of writing | |
1414 | ||
1415 | cp = strcpy (foo, "lkj"); | |
1416 | ||
1417 | one can write | |
1418 | ||
1419 | cp = (strcpy) (foo, "lkj"); | |
1420 | ||
1421 | This disables the optimization for that specific call. | |
1422 | ||
1423 | ||
1424 | 3.9. I get compiler messages "Initializer element not constant" with | |
1425 | stdin/stdout/stderr. Why? | |
1426 | ||
1427 | {RM,AJ} Constructs like: | |
1428 | static FILE *InPtr = stdin; | |
1429 | ||
1430 | lead to this message. This is correct behaviour with glibc since stdin is | |
1431 | not a constant expression. Please note that a strict reading of ISO C does | |
1432 | not allow above constructs. | |
1433 | ||
1434 | One of the advantages of this is that you can assign to stdin, stdout, and | |
1435 | stderr just like any other global variable (e.g. `stdout = my_stream;'), | |
1436 | which can be very useful with custom streams that you can write with libio | |
1437 | (but beware this is not necessarily portable). The reason to implement it | |
1438 | this way were versioning problems with the size of the FILE structure. | |
1439 | ||
1440 | To fix those programs you've got to initialize the variable at run time. | |
1441 | This can be done, e.g. in main, like: | |
1442 | ||
1443 | static FILE *InPtr; | |
1444 | int main(void) | |
1445 | { | |
1446 | InPtr = stdin; | |
1447 | } | |
1448 | ||
1449 | or by constructors (beware this is gcc specific): | |
1450 | ||
1451 | static FILE *InPtr; | |
1452 | static void inPtr_construct (void) __attribute__((constructor)); | |
1453 | static void inPtr_construct (void) { InPtr = stdin; } | |
1454 | ||
1455 | ||
1456 | 3.10. I can't compile with gcc -traditional (or | |
1457 | -traditional-cpp). Why? | |
1458 | ||
1459 | {AJ} glibc2 does break -traditional and -traditonal-cpp - and will continue | |
1460 | to do so. For example constructs of the form: | |
1461 | ||
1462 | enum {foo | |
1463 | #define foo foo | |
1464 | } | |
1465 | ||
1466 | are useful for debugging purposes (you can use foo with your debugger that's | |
1467 | why we need the enum) and for compatibility (other systems use defines and | |
1468 | check with #ifdef). | |
1469 | ||
1470 | ||
1471 | 3.11. I get some errors with `gcc -ansi'. Isn't glibc ANSI compatible? | |
1472 | ||
1473 | {AJ} The GNU C library is compatible with the ANSI/ISO C standard. If | |
1474 | you're using `gcc -ansi', the glibc includes which are specified in the | |
1475 | standard follow the standard. The ANSI/ISO C standard defines what has to be | |
1476 | in the include files - and also states that nothing else should be in the | |
1477 | include files (btw. you can still enable additional standards with feature | |
1478 | flags). | |
1479 | ||
1480 | The GNU C library is conforming to ANSI/ISO C - if and only if you're only | |
1481 | using the headers and library functions defined in the standard. | |
1482 | ||
1483 | ||
1484 | 3.12. I can't access some functions anymore. nm shows that they do | |
1485 | exist but linking fails nevertheless. | |
1486 | ||
1487 | {AJ} With the introduction of versioning in glibc 2.1 it is possible to | |
1488 | export only those identifiers (functions, variables) that are really needed | |
1489 | by application programs and by other parts of glibc. This way a lot of | |
1490 | internal interfaces are now hidden. nm will still show those identifiers | |
1491 | but marking them as internal. ISO C states that identifiers beginning with | |
1492 | an underscore are internal to the libc. An application program normally | |
1493 | shouldn't use those internal interfaces (there are exceptions, | |
1494 | e.g. __ivaliduser). If a program uses these interfaces, it's broken. These | |
1495 | internal interfaces might change between glibc releases or dropped | |
1496 | completely. | |
1497 | ||
1498 | ||
1499 | 3.13. When using the db-2 library which comes with glibc is used in | |
1500 | the Perl db modules the testsuite is not passed. This did not | |
1501 | happen with db-1, gdbm, or ndbm. | |
1502 | ||
1503 | Removed. Does not apply anymore. | |
1504 | ||
1505 | ||
1506 | ||
1507 | ||
1508 | 3.14. The pow() inline function I get when including <math.h> is broken. | |
1509 | I get segmentation faults when I run the program. | |
1510 | ||
1511 | {UD} Nope, the implementation is correct. The problem is with egcs version | |
1512 | prior to 1.1. I.e., egcs 1.0 to 1.0.3 are all broken (at least on Intel). | |
1513 | If you have to use this compiler you must define __NO_MATH_INLINES before | |
1514 | including <math.h> to prevent the inline functions from being used. egcs 1.1 | |
1515 | fixes the problem. I don't know about gcc 2.8 and 2.8.1. | |
1516 | ||
1517 | ||
1518 | 3.15. The sys/sem.h file lacks the definition of `union semun'. | |
1519 | ||
1520 | {UD} Nope. This union has to be provided by the user program. Former glibc | |
1521 | versions defined this but it was an error since it does not make much sense | |
1522 | when thinking about it. The standards describing the System V IPC functions | |
1523 | define it this way and therefore programs must be adopted. | |
1524 | ||
1525 | ||
1526 | 3.16. Why has <netinet/ip_fw.h> disappeared? | |
1527 | ||
1528 | {AJ} The corresponding Linux kernel data structures and constants are | |
1529 | totally different in Linux 2.0 and Linux 2.2. This situation has to be | |
1530 | taken care in user programs using the firewall structures and therefore | |
1531 | those programs (ipfw is AFAIK the only one) should deal with this problem | |
1532 | themselves. | |
1533 | ||
1534 | ||
1535 | 3.17. I get floods of warnings when I use -Wconversion and include | |
1536 | <string.h> or <math.h>. | |
1537 | ||
1538 | {ZW} <string.h> and <math.h> intentionally use prototypes to override | |
1539 | argument promotion. -Wconversion warns about all these. You can safely | |
1540 | ignore the warnings. | |
1541 | ||
1542 | -Wconversion isn't really intended for production use, only for shakedown | |
1543 | compiles after converting an old program to standard C. | |
1544 | ||
1545 | ||
1546 | 3.18. After upgrading to glibc 2.1, I receive errors about | |
1547 | unresolved symbols, like `_dl_initial_searchlist' and can not | |
1548 | execute any binaries. What went wrong? | |
1549 | ||
1550 | {AJ} This normally happens if your libc and ld (dynamic linker) are from | |
1551 | different releases of glibc. For example, the dynamic linker | |
1552 | /lib/ld-linux.so.2 comes from glibc 2.0.x, but the version of libc.so.6 is | |
1553 | from glibc 2.1. | |
1554 | ||
1555 | The path /lib/ld-linux.so.2 is hardcoded in every glibc2 binary but | |
1556 | libc.so.6 is searched via /etc/ld.so.cache and in some special directories | |
1557 | like /lib and /usr/lib. If you run configure with another prefix than /usr | |
1558 | and put this prefix before /lib in /etc/ld.so.conf, your system will break. | |
1559 | ||
1560 | So what can you do? Either of the following should work: | |
1561 | ||
1562 | * Run `configure' with the same prefix argument you've used for glibc 2.0.x | |
1563 | so that the same paths are used. | |
1564 | * Replace /lib/ld-linux.so.2 with a link to the dynamic linker from glibc | |
1565 | 2.1. | |
1566 | ||
1567 | You can even call the dynamic linker by hand if everything fails. You've | |
1568 | got to set LD_LIBRARY_PATH so that the corresponding libc is found and also | |
1569 | need to provide an absolute path to your binary: | |
1570 | ||
1571 | LD_LIBRARY_PATH=<path-where-libc.so.6-lives> \ | |
1572 | <path-where-corresponding-dynamic-linker-lives>/ld-linux.so.2 \ | |
1573 | <path-to-binary>/binary | |
1574 | ||
1575 | For example `LD_LIBRARY_PATH=/libold /libold/ld-linux.so.2 /bin/mv ...' | |
1576 | might be useful in fixing a broken system (if /libold contains dynamic | |
1577 | linker and corresponding libc). | |
1578 | ||
1579 | With that command line no path is used. To further debug problems with the | |
1580 | dynamic linker, use the LD_DEBUG environment variable, e.g. | |
1581 | `LD_DEBUG=help echo' for the help text. | |
1582 | ||
1583 | If you just want to test this release, don't put the lib directory in | |
1584 | /etc/ld.so.conf. You can call programs directly with full paths (as above). | |
1585 | When compiling new programs against glibc 2.1, you've got to specify the | |
1586 | correct paths to the compiler (option -I with gcc) and linker (options | |
1587 | --dynamic-linker, -L and --rpath). | |
1588 | ||
1589 | ||
1590 | 3.19. bonnie reports that char i/o with glibc 2 is much slower than with | |
1591 | libc5. What can be done? | |
1592 | ||
1593 | {AJ} The GNU C library uses thread safe functions by default and libc5 used | |
1594 | non thread safe versions. The non thread safe functions have in glibc the | |
1595 | suffix `_unlocked', for details check <stdio.h>. Using `putc_unlocked' etc. | |
1596 | instead of `putc' should give nearly the same speed with bonnie (bonnie is a | |
1597 | benchmark program for measuring disk access). | |
1598 | ||
1599 | ||
1600 | 3.20. Programs compiled with glibc 2.1 can't read db files made with glibc | |
1601 | 2.0. What has changed that programs like rpm break? | |
1602 | ||
1603 | Removed. Does not apply anymore. | |
1604 | ||
1605 | ||
1606 | ||
1607 | ||
1608 | 3.21. Autoconf's AC_CHECK_FUNC macro reports that a function exists, but | |
1609 | when I try to use it, it always returns -1 and sets errno to ENOSYS. | |
1610 | ||
1611 | {ZW} You are using a 2.0 Linux kernel, and the function you are trying to | |
1612 | use is only implemented in 2.1/2.2. Libc considers this to be a function | |
1613 | which exists, because if you upgrade to a 2.2 kernel, it will work. One | |
1614 | such function is sigaltstack. | |
1615 | ||
1616 | Your program should check at runtime whether the function works, and | |
1617 | implement a fallback. Note that Autoconf cannot detect unimplemented | |
1618 | functions in other systems' C libraries, so you need to do this anyway. | |
1619 | ||
1620 | ||
1621 | 3.22. My program segfaults when I call fclose() on the FILE* returned | |
1622 | from setmntent(). Is this a glibc bug? | |
1623 | ||
1624 | {GK} No. Don't do this. Use endmntent(), that's what it's for. | |
1625 | ||
1626 | In general, you should use the correct deallocation routine. For instance, | |
1627 | if you open a file using fopen(), you should deallocate the FILE * using | |
1628 | fclose(), not free(), even though the FILE * is also a pointer. | |
1629 | ||
1630 | In the case of setmntent(), it may appear to work in most cases, but it | |
1631 | won't always work. Unfortunately, for compatibility reasons, we can't | |
1632 | change the return type of setmntent() to something other than FILE *. | |
1633 | ||
1634 | \f | |
1635 | . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . | |
1636 | ||
1637 | 4. Miscellaneous | |
1638 | ||
1639 | 4.1. After I changed configure.in I get `Autoconf version X.Y. | |
1640 | or higher is required for this script'. What can I do? | |
1641 | ||
1642 | {UD} You have to get the specified autoconf version (or a later one) | |
1643 | from your favorite mirror of ftp.gnu.org. | |
1644 | ||
1645 | ||
1646 | 4.2. When I try to compile code which uses IPv6 headers and | |
1647 | definitions on my Linux 2.x.y system I am in trouble. | |
1648 | Nothing seems to work. | |
1649 | ||
1650 | {UD} The problem is that IPv6 development still has not reached a point | |
1651 | where the headers are stable. There are still lots of incompatible changes | |
1652 | made and the libc headers have to follow. | |
1653 | ||
1654 | {PB} The 2.1 release of GNU libc aims to comply with the current versions of | |
1655 | all the relevant standards. The IPv6 support libraries for older Linux | |
1656 | systems used a different naming convention and so code written to work with | |
1657 | them may need to be modified. If the standards make incompatible changes in | |
1658 | the future then the libc may need to change again. | |
1659 | ||
1660 | IPv6 will not work with a 2.0.x kernel. When kernel 2.2 is released it | |
1661 | should contain all the necessary support; until then you should use the | |
1662 | latest 2.1.x release you can find. As of 98/11/26 the currently recommended | |
1663 | kernel for IPv6 is 2.1.129. | |
1664 | ||
1665 | Also, as of the 2.1 release the IPv6 API provided by GNU libc is not | |
1666 | 100% complete. In particular the getipnodebyname and getipnodebyaddr | |
1667 | functions are not implemented. | |
1668 | ||
1669 | ||
1670 | 4.3. When I set the timezone by setting the TZ environment variable | |
1671 | to EST5EDT things go wrong since glibc computes the wrong time | |
1672 | from this information. | |
1673 | ||
1674 | {UD} The problem is that people still use the braindamaged POSIX method to | |
1675 | select the timezone using the TZ environment variable with a format EST5EDT | |
1676 | or whatever. People, if you insist on using TZ instead of the timezone | |
1677 | database (see below), read the POSIX standard, the implemented behaviour is | |
1678 | correct! What you see is in fact the result of the decisions made while | |
1679 | POSIX.1 was created. We've only implemented the handling of TZ this way to | |
1680 | be POSIX compliant. It is not really meant to be used. | |
1681 | ||
1682 | The alternative approach to handle timezones which is implemented is the | |
1683 | correct one to use: use the timezone database. This avoids all the problems | |
1684 | the POSIX method has plus it is much easier to use. Simply run the tzselect | |
1685 | shell script, answer the question and use the name printed in the end by | |
1686 | making a symlink /etc/localtime pointing to /usr/share/zoneinfo/NAME (NAME | |
1687 | is the returned value from tzselect). That's all. You never again have to | |
1688 | worry. | |
1689 | ||
1690 | So, please avoid sending bug reports about time related problems if you use | |
1691 | the POSIX method and you have not verified something is really broken by | |
1692 | reading the POSIX standards. | |
1693 | ||
1694 | ||
1695 | 4.4. What other sources of documentation about glibc are available? | |
1696 | ||
1697 | {AJ} The FSF has a page about the GNU C library at | |
1698 | <http://www.gnu.org/software/libc/>. The problem data base of open and | |
1699 | solved bugs in GNU libc is available at | |
1700 | <http://www-gnats.gnu.org:8080/cgi-bin/wwwgnats.pl>. Eric Green has written | |
1701 | a HowTo for converting from Linux libc5 to glibc2. The HowTo is accessible | |
1702 | via the FSF page and at <http://www.imaxx.net/~thrytis/glibc>. Frodo | |
1703 | Looijaard describes a different way installing glibc2 as secondary libc at | |
1704 | <http://huizen.dds.nl/~frodol/glibc>. | |
1705 | ||
1706 | Please note that this is not a complete list. | |
1707 | ||
1708 | ||
1709 | 4.5. The timezone string for Sydney/Australia is wrong since even when | |
1710 | daylight saving time is in effect the timezone string is EST. | |
1711 | ||
1712 | {UD} The problem for some timezones is that the local authorities decided | |
1713 | to use the term "summer time" instead of "daylight saving time". In this | |
1714 | case the abbreviation character `S' is the same as the standard one. So, | |
1715 | for Sydney we have | |
1716 | ||
1717 | Eastern Standard Time = EST | |
1718 | Eastern Summer Time = EST | |
1719 | ||
1720 | Great! To get this bug fixed convince the authorities to change the laws | |
1721 | and regulations of the country this effects. glibc behaves correctly. | |
1722 | ||
1723 | ||
1724 | 4.6. I've build make 3.77 against glibc 2.1 and now make gets | |
1725 | segmentation faults. | |
1726 | ||
1727 | {AJ} GNU make 3.77 has support for 64 bit filesystems which is slightly | |
1728 | broken (and one of the new features in the GNU C library 2.1 is 64 bit | |
1729 | filesystem support :-( ). To get a working make you can use either make | |
1730 | 3.75 or patch 3.77. A working patch is available via RedHat's Rawhide server | |
1731 | (ftp://rawhide.redhat.com/SRPMS/SRPMS/make-3.77-*src.rpm). | |
1732 | ||
1733 | ||
1734 | 4.7. Why do so many programs using math functions fail on my AlphaStation? | |
1735 | ||
1736 | {AO} The functions floor() and floorf() use an instruction that is not | |
1737 | implemented in some old PALcodes of AlphaStations. This may cause | |
1738 | `Illegal Instruction' core dumps or endless loops in programs that | |
1739 | catch these signals. Updating the firmware to a 1999 release has | |
1740 | fixed the problem on an AlphaStation 200 4/166. | |
1741 | ||
1742 | ||
1743 | 4.8. The conversion table for character set XX does not match with | |
1744 | what I expect. | |
1745 | ||
1746 | {UD} I don't doubt for a minute that some of the conversion tables contain | |
1747 | errors. We tried the best we can and relied on automatic generation of the | |
1748 | data to prevent human-introduced errors but this still is no guarantee. If | |
1749 | you think you found a problem please send a bug report describing it and | |
1750 | give an authoritive reference. The latter is important since otherwise | |
1751 | the current behaviour is as good as the proposed one. | |
1752 | ||
1753 | Before doing this look through the list of known problem first: | |
1754 | ||
1755 | - the GBK (simplified Chinese) encoding is based on Unicode tables. This | |
1756 | is good. These tables, however, differ slightly from the tables used | |
1757 | by the M$ people. The differences are these [+ Unicode, - M$]: | |
1758 | ||
1759 | +0xA1AA 0x2015 | |
1760 | +0xA844 0x2014 | |
1761 | -0xA1AA 0x2014 | |
1762 | -0xA844 0x2015 | |
1763 | ||
1764 | In addition the Unicode tables contain mappings for the GBK characters | |
1765 | 0xA8BC, 0xA8BF, 0xA989 to 0xA995, and 0xFE50 to 0xFEA0. | |
1766 | ||
1767 | - when mapping from EUC-CN to GBK and vice versa we ignore the fact that | |
1768 | the coded character at position 0xA1A4 maps to different Unicode | |
1769 | characters. Since the iconv() implementation can do whatever it wants | |
1770 | if it cannot directly map a character this is a perfectly good solution | |
1771 | since the semantics and appearance of the character does not change. | |
1772 | ||
1773 | \f | |
1774 | ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | |
1775 | ||
1776 | Answers were given by: | |
1777 | {UD} Ulrich Drepper, <drepper@cygnus.com> | |
1778 | {DMT} David Mosberger-Tang, <davidm@AZStarNet.com> | |
1779 | {RM} Roland McGrath, <roland@gnu.org> | |
1780 | {AJ} Andreas Jaeger, <aj@suse.de> | |
1781 | {EY} Eric Youngdale, <eric@andante.jic.com> | |
1782 | {PB} Phil Blundell, <Philip.Blundell@pobox.com> | |
1783 | {MK} Mark Kettenis, <kettenis@phys.uva.nl> | |
1784 | {ZW} Zack Weinberg, <zack@rabi.phys.columbia.edu> | |
1785 | {TK} Thorsten Kukuk, <kukuk@suse.de> | |
1786 | {GK} Geoffrey Keating, <geoffk@ozemail.com.au> | |
1787 | {HJ} H.J. Lu, <hjl@gnu.org> | |
1788 | {CG} Cristian Gafton, <gafton@redhat.com> | |
1789 | {AO} Alexandre Oliva, <oliva@lsd.ic.unicamp.br> | |
1790 | \f | |
1791 | Local Variables: | |
1792 | mode:outline | |
1793 | outline-regexp:"\\?" | |
1794 | fill-column:76 | |
1795 | End: |