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From: "gauryogesh.nsit at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/55872] Crash issue with RTLD_DEEPBIND usage with stdc++ library
Date: Mon, 07 Jan 2013 10:31:00 -0000
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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.