/usr/lib64/libc.so是如何生成的？

Question

[root@xx test]# cat /usr/lib64/libc.so
/* GNU ld script
   Use the shared library, but some functions are only in
   the static library, so try that secondarily.  */
OUTPUT_FORMAT(elf64-x86-64)
GROUP ( /lib64/libc.so.6 /usr/lib64/libc_nonshared.a  AS_NEEDED ( /lib64/ld-linux-x86-64.so.2 ) )

谁知道这种东西是如何产生的？

Answer 1

使用Make实用程序编译glibc时会生成此错误.

make install在glibc的Makefile中有一条规则(由...开始),它只需将所需的行回显到一些临时文件中$@.new:

(echo '/* GNU ld script';\
 echo '   Use the shared library, but some functions are only in';\
 echo '   the static library, so try that secondarily.  */';\
 cat $<; \
 echo 'GROUP ( $(slibdir)/libc.so$(libc.so-version)' \
      '$(libdir)/$(patsubst %,$(libtype.oS),$(libprefix)$(libc-name))'\
      ' AS_NEEDED (' $(slibdir)/$(rtld-installed-name) ') )' \
) > $@.new

然后将此文件重命名为 libc.so

mv -f $@.new $@

这是Makefile的注释,它解释了一下:

# What we install as libc.so for programs to link against is in fact a
# link script.  It contains references for the various libraries we need.
# The libc.so object is not complete since some functions are only defined
# in libc_nonshared.a.
# We need to use absolute paths since otherwise local copies (if they exist)
# of the files are taken by the linker.

我理解为:libc.so.6不完整,需要一些东西,不能存储在共享库中.所以,glibc开发人员将这个东西移到glibc的静态部分 - libc_nonshared.a.要强制始终联系两者的libc.so.6和libc_nonstared.a,他们创造了一个特殊链接脚本命令LD链接器同时使用时,它要求-lc(的libc)

什么是非共享部分？让我们检查:

$ objdump -t /usr/lib/libc_nonshared.a |grep " F "|grep -v __
00000000 g     F .text  00000058 .hidden atexit
00000000  w    F .text  00000050 .hidden stat
00000000  w    F .text  00000050 .hidden fstat
00000000  w    F .text  00000050 .hidden lstat
00000000 g     F .text  00000050 .hidden stat64
00000000 g     F .text  00000050 .hidden fstat64
00000000 g     F .text  00000050 .hidden lstat64
00000000 g     F .text  00000050 .hidden fstatat
00000000 g     F .text  00000050 .hidden fstatat64
00000000  w    F .text  00000058 .hidden mknod
00000000 g     F .text  00000050 .hidden mknodat
00000000 l     F .text  00000001 nop

有atexit(),*stat*(),mknod等功能.为什么？真的不知道,但这是glibc的事实.

这里有一些长篇解释http://giraffe-data.com/~bryanh/giraffehome/d/note/proglib,我引用它的开头:

The stat() family of functions and mknod() are special.  Their
interfaces are tied so tightly to the underlying operating system that
they change occasionally.