https://sourceware.org/bugzilla/show_bug.cgi?id=26762
Bug ID: 26762
Summary: -Wl,--as-needed removes strong symbols in favour of
weak symbols
Product: binutils
Version: 2.34
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: slyfox at inbox dot ru
CC: ccoutant at gmail dot com
Target Milestone: ---
Original bug was a failed attempt to build llvm-11 with LDFLAGS="-flto
-Wl,--as-needed": https://bugs.gentoo.org/749162.
There std::call_once is implemented via weak pthread_once() symbol:
https://gcc.gnu.org/PR55394. Presence of -Wl,--as-needed removes libpthread.so
and breaks the program at runtime as pthread_once() has to have a real
implementation. gcc plans to fix std::call_once by avoiding pthread_once() for
unrelated reason (solving it will take a while).
But the problem seems to be more general when local weak symbols are used to
probe presence of a real implementation dynamically.
What do you think of changing 'ld' to prefer strong symbols from shared
libraries and keeping DT_NEEDED entries even if local object files define weak
symbols?
Toy example:
$ cat a.c
// gcc a.c -o a -Wl,--as-needed -pthread && ./a
#include <stdio.h>
#include <pthread.h>
static pthread_once_t once = PTHREAD_ONCE_INIT;
static __typeof(pthread_once) __gthrw_pthread_once __attribute__
((__weakref__("pthread_once"), __copy__ (pthread_once)));
static void ir(void)
{
printf("foo\n");
}
int main(void)
{
if (__gthrw_pthread_once)
__gthrw_pthread_once(&once, &ir);
}
$ gcc a.c -o a -Wl,--as-needed -pthread -fuse-ld=bfd && ./a
$ gcc a.c -o a -Wl,--as-needed -pthread -fuse-ld=gold && ./a
$ gcc a.c -o a -Wl,--as-needed -pthread -fuse-ld=lld && ./a
$ gcc a.c -o a -Wl,--no-as-needed -pthread -fuse-ld=bfd && ./a
foo
Ideally all 4 tests should call pthread_once from libpthread.so.0 instead of
calling local weak reference.
Thanks!
--
You are receiving this mail because:
You are on the CC list for the bug.
