http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55872
--- Comment #4 from Yogesh Gaur <gauryogesh.nsit at gmail dot com> 2013-01-07
10:31:19 UTC ---
Hello,
Actually issue is combination of copy_relocation plus RTLD_DEEPBIND flag.
If I didn't give -fPIE flag while compiling my executable and pass
RTLD_DEEPBIND flag while opening library using dlopen(), then result is
un-expected.
I checked similar issue exist on gcc also:
------------------------------Source Code -----------------------------
$ cat main.c
#include <dlfcn.h>
extern int alpha;
int main()
{
char const * const name = "./lib1.so";
void * handle = dlopen(name, RTLD_NOW | RTLD_LOCAL | RTLD_DEEPBIND);
typedef void (*library_function_type)();
library_function_type func1 = dlsym(handle, "func1");
alpha = 10;
(*func1)();
func2();
dlclose(handle);
return 0;
}
$ cat lib1.c
#include <stdio.h>
extern int alpha;
void func1(){
printf("lib1: Addr=%p, value=%d\n", &alpha, alpha);
}
$ cat lib2.c
#include <stdio.h>
int alpha;
void func2(){
printf("lib2: Addr=%p, value=%d\n", &alpha, alpha);
}
-------------------------------- END ----------------------------------
Compilation command and output:
gcc -shared -fPIC lib2.c -o lib2.so
gcc -shared -fPIC lib1.c lib2.so -o lib1.so
gcc -ldl main.c lib2.so -o a.out
LD_LIBRARY_PATH=$PWD ./a.out
lib1: Addr=0x7f5a39663028, value=0
lib2: Addr=0x601038, value=10
=========================================
Thus for same symbol, alpha, we get two addresses values.
If I remove RTLD_DEEPBIND while opening library, I didn't get this issue:
lib1: Addr=0x601038, value=10
lib2: Addr=0x601038, value=10
Reason for this also I know that in case of RTLD_DEEPBIND scope of search for
lib1.so is its internal library first and then only global library's being
searched.
I want to know that apart from usage of -fPIE flag at compilation time did
any-other solution exist for this issue? As using -fPIE has it's own
side-affect.
--
Regards,
Yogesh Gaur.
