1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
|
Frequently Asked Question on GNU C Library
As every FAQ this one also tries to answer the questions the user
might when using the pacakge. Please make sure you read this before
sending questions/bug reports to the maintainers.
The GNU C Library is very complex. The building process exploits the
features available in tools generally available. But many things can
only be done using GNU tools. Also the code is sometimes hard to
understand because it has to be portable but on the other hand must be
fast. But you need not understand the details to use GNU C Library.
This will only be necessary if you intend to contribute or change it.
If you have any question which you think might be worth answered in
this document let me know.
--drepper@cygnus.com
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q1] ``What systems the GNU C Library runs on?''
[Q2] ``What compiler do I need to translate GNU libc?''
[Q3] ``When starting make I get only errors messages.
What's wrong?''
[Q4] ``After I changed configure.in I get `Autoconf version X.Y.
or higher is required for this script'. What can I do?''
[Q5] ``Do I need a special linker or archiver?''
[Q6] ``Do I need some more things to compile GNU C Library?''
[Q7] ``When I run `nm libc.so|grep " U "' on the produced library
I still find unresolved symbols? Can this be ok?''
[Q8] ``I expect GNU libc to be 100% source code compatible with
the old Linux based GNU libc. Why isn't it like this?''
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q1] ``What systems the GNU C Library runs on?''
[A1] {UD} This is difficult to answer. The file `README' lists the
architectures GNU libc is known to run *at some time*. This does not
mean that it still can be compiled and run on them in the moment.
The systems glibc is known to work on in the moment and most probably
in the future are:
*-*-gnu GNU Hurd
i[3456]86-*-linux Linux-2.0 on Intel
Other Linux platforms are also on the way to be supported but I need
some success reports first.
If you have a system not listed above (or in the `README' file) and
you are really interested in porting it, contact
Roland McGrath <roland@gnu.ai.mit.edu>
or Ulrich Drepper <drepper@cygnus.com>
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q2] ``What compiler do I need to translate GNU libc?''
[A2] {UD} It is (almost) impossible to compile GNU C Library using a
different compiler than GNU CC. A lot of extensions of GNU CC are
used to increase the portability and speed.
But this does not mean you have to use GNU CC for using the GNU C
Library. In fact you should be able to use the native C compiler
because the success only depends on the binutils: the linker and
archiver.
The GNU CC is found like all other GNU packages on
ftp://prep.ai.mit.edu/pub/gnu
or better one of the many mirrors.
You always should try to use the latest official release. Older
versions might not have all the features GNU libc could use.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q3] ``When starting make I get only errors messages.
What's wrong?''
[A3] {UD} You definitely need GNU make to translate GNU libc. No
other make program has the needed functionality.
Versions before 3.74 have bugs which prevent correct execution so you
should upgrade to the latest version before starting the compilation.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q4] ``After I changed configure.in I get `Autoconf version X.Y.
or higher is required for this script'. What can I do?''
[A4] {UD} You have to get the specified autoconf version (or a later)
from your favourite mirror of prep.ai.mit.edu.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q5] ``Do I need a special linker or archiver?''
[A5] {UD} If your native versions are not too buggy you can work with
them. But GNU libc works best with GNU binutils.
On systems where the native linker does not support weak symbols you
will not get a really ISO C compliant C library. Generally speaking
you should use the GNU binutils if they provide at least the same
functionality as your system's tools.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q6] ``Do I need some more things to compile GNU C Library?''
[A6] {UD} Yes, there are some more :-).
* lots of diskspace (for i386-linux this means, e.g., ~70MB)
You should avoid compiling on a NFS mounted device. This is very
slow.
* plenty of time (approx 1h for i386-linux on i586@133 or 2.5h or
i486@66).
If you have some more interested measurements let me know.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q7] ``When I run `nm libc.so|grep " U "' on the produced library
I still find unresolved symbols? Can this be ok?''
[A7] {UD} Yes, this is ok. There can be several kinds of unresolved
symbols:
* magic symbols automatically generated by the linker. Names are
often like __start_* and __stop_*-
* symbols resolved by using libgcc.a
(__udivdi3, __umoddi3, or similar)
* weak symbols, which need not be resolved at all
(currently fabs among others; this gets resolved if the program
is linked against libm, too.)
Generally, you should make sure you find a real program which produces
errors while linking.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
[Q8] ``I expect GNU libc to be 100% source code compatible with
the old Linux based GNU libc. Why isn't it like this?''
[A8] {DMT} Not every extension in Linux libc's history was well
thought. In fact it had a lot of problems with standard compliance
and cleanliness. With the introduction of a new version number these
errors now can be corrected. The following list shows a list of the
know source code incompatibilities.
* _GNU_SOURCE: glibc does not automatically define _GNU_SOURCE. Thus,
if a program depends on GNU extensions, it is necessary
to compile it with C compiler option -D_GNU_SOURCE. This difference
normally mainfests itself in the form of missing prototypes and/or
data type definitions. Thus, if you get such errors, the first thing you
should do is grep the header files in /usr/include and /usr/include/sys
to check whether the functions are really missing or whether it is
just necessary to add a define of _GNU_SOURCE. Similar comments apply
to _BSD_SOURCE, _POSIX_SOURCE, _SVID_SOURCE etc (see
/usr/include/features.h).
* reboot(): GNU libc sanitizes the interface of reboot() to be more
compatible with the interface used on other OSes. In particular,
reboot() as implemented in glibc takes just one argument. This argument
corresponds to the third argument of the Linux reboot system call.
That is, a call of the form reboot(a, b, c) needs to be changed into
reboot(c).
* errno: If a program uses variable "errno", then it _must_ include header
file <errno.h>. The old libc often (erroneously) declared this variable
implicitly as a side-effect of including other libc header files. glibc
is careful to avoid such namespace pollution, which, in turn, means that
you really need to include the header files that you depend on. This
difference normally manifests itself in the form of the compiler
complaining about the references of the undeclared symbol "errno".
* Linux-specific syscalls: All Linux system calls now have appropriate
library wrappers and corresponding declarations in various header files.
This is because the syscall() macro that was traditionally used to
work around missing syscall wrappers are inherently non-portable and
error-prone. The following tables lists all the new syscall stubs,
the header-file declaring their interface and the system call name.
syscall name: wrapper name: declaring header file:
------------- ------------- ----------------------
bdflush bdflush <unistd.h>
create_module create_module <sys/module.h>
delete_module delete_module <sys/module.h>
get_kernel_syms get_kernel_syms <sys/module.h>
init_module init_module <sys/module.h>
syslog ksyslog_ctl <unistd.h>
To get the Linux-specific declarations in <unistd.h>, you'll need
to define C pre-processor macro _LINUX_SOURCE during compilation.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
Answers were given by:
{UD} Ulrich Drepper, <drepper@cygnus.com>
{DMT} David Mosberger-Tang, <davidm@AZStarNet.com>
Local Variables:
mode:text
End:
|
