Add two rtld exported symbols, _rtld_atfork_pre and _rtld_atfork_post.

Threading library calls _pre before the fork, allowing the rtld to
lock itself to ensure that other threads of the process are out of
dynamic linker. _post releases the locks.

This allows the rtld to have consistent state in the child. Although
child may legitimately call only async-safe functions, the call may
need plt relocation resolution, and this requires working rtld.

Reported and debugging help by:	rink
Reviewed by:	kan, davidxu
MFC after:	1 month (anyway, not before 7.1 is out)

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/libc/gen/Symbol.map b/lib/libc/gen/Symbol.map
index 6e8bfce..2e64313 100644
--- a/lib/libc/gen/Symbol.map
+++ b/lib/libc/gen/Symbol.map
@@ -432,6 +432,8 @@ FBSDprivate_1.0 {
 	_spinlock;
 	_spinlock_debug;
 	_spinunlock;
+	_rtld_atfork_pre;
+	_rtld_atfork_post;
 	_rtld_error;		/* for private use */
 	_rtld_thread_init;	/* for private use */
 	_err;