symbol-file

Although still I do NOT know now to extract a symbol file from
unstripped binary executable, but seems I got a solution. -_-

% echo "int main(void) {return 0; }" > foo.c
% gcc -ggdb foo.c -o foo.gdb
% gcc -s foo.c -o foo
% gdb -q foo
(no debugging symbols found)
Using host libthread_db library "/lib/libthread_db.so.1".
(gdb) b main
Function "main" not defined.
Make breakpoint pending on future shared library load? (y or [n]) n
(gdb) symbol-file foo.gdb
Reading symbols from /home/david/foo.gdb...done.
(gdb) b main
Breakpoint 1 at 0x8048352: file foo.c, line 1.
(gdb) l
1 int main(void) {return 0; }
(gdb)