Re: force symbols for inline functions to be addressed at a particular library

["Peter McAlpine" <petermca at gmail dot com>]

Sorry to re-post, but does anyone have suggestions on how to force g++
to link against libc for 'stat' symbol instead of using the weak
symbol from my shared library?

Any help would be greatly appreciated.
-Peter

On 9/24/07, Peter McAlpine <petermca@gmail.com> wrote:
> Hello,
>
> I have written a program and shared library, both of which use the
> libc stat function. I want to build optimized and non-optimized
> versions of each, and then run the optimized program against the
> non-optimized library.
>
> The stat function is inline, and thus the optimized version of my
> shared library does not actually have the stat symbol.
>
> My non-optimized program was compiled and linked against the
> non-optimized library, and for some reason when g++ links my program
> it thinks stat symbol should be found in my shared library. In fact it
> should be found in libc.
>
> At runtime, my non-optimized program looks for the stat symbol in my
> (optimized) shared library, but because the shared library has had the
> (inline) stat symbol optimized out I get a runtime error:
> undefined symbol: stat
>
> If anyone can give me some direction on how to get g++ to use the libc
> stat symbol instead of my shared library's stat symbol I'd greatly
> appreciate it.
>
> Thanks,
> -Peter
>
> PS - Below is the code/script I'm using to show this undesired behaviour.
> ################# t.sh (compile/run) ######################
> #! /bin/bash -v
> # build non-O libfoo
> g++ -O0 -c -o foo.o foo.cpp
> g++ -O0 -shared -o libfoo_no.so foo.o
>
> # build O libfoo
> g++ -O -c -o foo.o foo.cpp
> g++ -O -shared -o libfoo_o.so foo.o
>
> # build t against no
> rm -f libfoo.so
> ln -s libfoo_no.so libfoo.so
> gcc -O0 -c -o t.o t.c
>
> # G++
> g++ -O0 -o t_no -L. t.o -lfoo
>
> echo
> # run t_no with o
> rm -f libfoo.so
> ln -s libfoo_o.so libfoo.so
> ./t_no
>
> ############## foo.cpp ##################
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <unistd.h>
> #include <stdio.h>
> #include "foo.h"
>
> int thefile(const char *path) {
>     struct stat statbuf;
>     int rc = 0;
>     printf("in thefile1: %s\n", path);
>     rc = stat(path, &statbuf);
>     printf("in thefile2: %s\n", path);
>     return rc;
> }
>
> ############# foo.h ############
> int thefile(const char *path);
>
> ############# t.c #############
> #include <stdio.h>
> #include <sys/stat.h>
> #include <sys/types.h>
> #include <unistd.h>
> #include "foo.h"
>
> ############### int main(int argc, char *argv) ##############
> {
>     struct stat attr;
>     printf("in main\n");
>     stat("/tmp/aoeu", &attr);
>     printf("in main2\n");
>
>     return 0;
> }
>
> ############ Output from compile/run ##################
> ./t.sh
> #! /bin/bash -v
> # build non-O libfoo
> g++ -O0 -c -o foo.o foo.cpp
> g++ -O0 -shared -o libfoo_no.so foo.o
>
> # build O libfoo
> g++ -O -c -o foo.o foo.cpp
> g++ -O -shared -o libfoo_o.so foo.o
>
> # build t against no
> rm -f libfoo.so
> ln -s libfoo_no.so libfoo.so
> gcc -O0 -c -o t.o t.c
>
> # G++
> g++ -O0 -o t_no -L. t.o -lfoo
>
> echo
>
> # run t_no with o
> rm -f libfoo.so
> ln -s libfoo_o.so libfoo.so
> ./t_no
> in main
> ./t_no: symbol lookup error: ./t_no: undefined symbol: stat
>