https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65886
--- Comment #6 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to H.J. Lu from comment #5)
>
> BTW, you should add -fsymbolic to -fPIC if the shared library will be
> created by -Bsymbolic. It will improve shared library performance.
Here is an example:
[hjl@gnu-tools-1 pr65886-lto]$ cat a.c
int a = -1;
[hjl@gnu-tools-1 pr65886-lto]$ cat b.c
extern int a;
void
bar ()
{
a = 30;
}
[hjl@gnu-tools-1 pr65886-lto]$ vi b.c
[hjl@gnu-tools-1 pr65886-lto]$ cat a.c
int a = -1;
[hjl@gnu-tools-1 pr65886-lto]$ cat b.c
extern int a;
void bar () { a = 30; }
[hjl@gnu-tools-1 pr65886-lto]$ make libb.so
/export/build/gnu/gcc-5/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc-5/build-x86_64-linux/gcc/ -g -O2 -fsymbolic -fPIC -flto
-c -o b.o b.c
/export/build/gnu/gcc-5/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc-5/build-x86_64-linux/gcc/ -g -O2 -fsymbolic -fPIC -flto
-c -o a.o a.c
/export/build/gnu/gcc-5/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc-5/build-x86_64-linux/gcc/ -flto -Wl,-Bsymbolic -g -O2
-fsymbolic -shared -o libb.so b.o a.o
[hjl@gnu-tools-1 pr65886-lto]$ gdb libb.so
GNU gdb (GDB) Fedora 7.8.2-38.fc21
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
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<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from libb.so...done.
(gdb) disass bar
Dump of assembler code for function bar:
0x00000000000005e0 <+0>: movl $0x1e,0x2002be(%rip) # 0x2008a8
<a>
0x00000000000005ea <+10>: retq
End of assembler dump.
(gdb)
