[Bug dynamic-link/15199] dlopening a load-time library from an earlier library's initializer corrupts TLS state

["luto at mit dot edu" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=15199

--- Comment #1 from Andy Lutomirski <luto at mit dot edu> 2013-02-26 19:06:57 UTC ---
Here's a self-contained testcase, tested on Fedora 18.

--- begin a.c ---
#include <dlfcn.h>

void a(void) {}
extern void abort(void);

__attribute__((constructor)) static void init(void)
{
  write(1, "dlopen b\n", 9);
  if (!dlopen("libb.so", RTLD_LAZY | RTLD_NOLOAD)) /* This corrupts TLS state
*/
    abort();
  write(1, "dlopen done\n", 12);
}
--- end a.c ---

--- begin b.c ---
static __thread int tls;

void b()
{
  write(1, "Begin TLS access\n", 17);
  tls = 1;  /* This will infinite loop because TLS state is corrupt */
  write(1, "Done\n", 5);
}
--- end b.c ---

--- begin main.c ---
extern void a(void), b(void);

int main()
{
  a();  /* Just to DT_NEEDED it. */
  b();  /* This one will hang. */
}
--- end main.c ---

To trigger the bug, do this:

$ gcc -g -fPIC -shared -o liba.so a.c
$ gcc -g -fPIC -shared -o libb.so b.c
$ gcc -g -o main main.c libb.so liba.so -ldl
$ LD_LIBRARY_PATH=. ./main
dlopen b
dlopen done
Begin TLS access
   [this infinite loops]

Reversing the link order of libb.so and liba.so will cause this code to work.

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