R_X86_64_TPOFF64 revealed by trivial testcase:
===================================================================
#include <stdio.h>
#include <errno.h>
int main() {
void *a = &errno;
printf("errno addr: %llx\n", a);
__asm__("movq errno@gottpoff(%%rip), %0;\n"
"add %%fs:0x0,%0;" : "=r"(a) );
printf("got errno addr: %llx\n", a);
return 0;
}
===================================================================
The addresses application got with R_X86_64_TPOFF64 was different than the once libc
internal __errno_location returned.
R_X86_64_DTPOFF64 testcase is even simpler than that:
===================================================================
#include <stdio.h>
#include <errno.h>
#include <netdb.h>
#undef h_errno
extern __thread int h_errno;
int main() {
printf("h_errno addr: %llx\n", &h_errno);
printf("__h_errno_location addr: %llx\n", __h_errno_location());
return 0;
}
===================================================================
but needs to be linked with "-lpthread". This way we've got h_errno relocation via
R_X86_64_TPOFF64 in application and h_errno relocation via R_X86_64_DTPOFF64 in
libpthread which has its own __h_errno_location() (probably we can kill it later?).
And addresses were different again.
The problem is that both relocations resolve symbols in external modules and thus
should use symbol_addr instead of sym->st_value.
Signed-off-by: Roman I Khimov <khimov@altell.ru>
Signed-off-by: Austin Foxley <austinf@cetoncorp.com>
case R_X86_64_DTPOFF64:
/* During relocation all TLS symbols are defined and used.
* Therefore the offset is already correct. */
- *reloc_addr = sym->st_value + rpnt->r_addend;
+ *reloc_addr = symbol_addr + rpnt->r_addend;
break;
case R_X86_64_TPOFF64:
/* The offset is negative, forward from the thread pointer.
* It is a negative value which will be added to the
* thread pointer. */
CHECK_STATIC_TLS ((struct link_map *) tls_tpnt);
- *reloc_addr = sym->st_value - tls_tpnt->l_tls_offset + rpnt->r_addend;
+ *reloc_addr = symbol_addr - tls_tpnt->l_tls_offset + rpnt->r_addend;
break;
case R_X86_64_32:
*(unsigned int *) reloc_addr = symbol_addr + rpnt->r_addend;