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
