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Add two rtld exported symbols, _rtld_atfork_pre and _rtld_atfork_post.

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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)
This commit is contained in:
Konstantin Belousov 2008-11-27 11:27:59 +00:00
parent 6974bd9e75
commit cb5c4b10ba
7 changed files with 46 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
lib/libc/gen/Symbol.map
View File

@ -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;

12
lib/libc/gen/dlfcn.c
View File

@ -137,3 +137,15 @@ dl_iterate_phdr(int (*callback)(struct dl_phdr_info *, size_t, void *),
_rtld_error(sorry);
return 0;
}
#pragma weak _rtld_atfork_pre
void
_rtld_atfork_pre(int *locks)
{
}
#pragma weak _rtld_atfork_post
void
_rtld_atfork_post(int *locks)
{
}

11
lib/libthr/thread/thr_fork.c
View File

@ -67,6 +67,7 @@
#include "un-namespace.h"
#include "libc_private.h"
#include "rtld_lock.h"
#include "thr_private.h"
__weak_reference(_pthread_atfork, pthread_atfork);
@ -105,6 +106,7 @@ _fork(void)
pid_t ret;
int errsave;
int unlock_malloc;
int rtld_locks[16];
if (!_thr_is_inited())
return (__sys_fork());
@ -127,6 +129,7 @@ _fork(void)
if (_thr_isthreaded() != 0) {
unlock_malloc = 1;
_malloc_prefork();
_rtld_atfork_pre(rtld_locks);
} else {
unlock_malloc = 0;
}
@ -167,6 +170,10 @@ _fork(void)
/* Ready to continue, unblock signals. */
_thr_signal_unblock(curthread);
if (unlock_malloc) {
_rtld_atfork_post(rtld_locks);
}
/* Run down atfork child handlers. */
TAILQ_FOREACH(af, &_thr_atfork_list, qe) {
if (af->child != NULL)
@ -179,8 +186,10 @@ _fork(void)
/* Ready to continue, unblock signals. */
_thr_signal_unblock(curthread);
if (unlock_malloc)
if (unlock_malloc) {
_rtld_atfork_post(rtld_locks);
_malloc_postfork();
}
/* Run down atfork parent handlers. */
TAILQ_FOREACH(af, &_thr_atfork_list, qe) {

2
libexec/rtld-elf/Symbol.map
View File

@ -21,4 +21,6 @@ FBSDprivate_1.0 {
_rtld_thread_init;
_rtld_allocate_tls;
_rtld_free_tls;
_rtld_atfork_pre;
_rtld_atfork_post;
};

2
libexec/rtld-elf/rtld.c
View File

@ -206,6 +206,8 @@ static func_ptr_type exports[] = {
(func_ptr_type) &_rtld_allocate_tls,
(func_ptr_type) &_rtld_free_tls,
(func_ptr_type) &dl_iterate_phdr,
(func_ptr_type) &_rtld_atfork_pre,
(func_ptr_type) &_rtld_atfork_post,
NULL
};

16
libexec/rtld-elf/rtld_lock.c
View File

@ -316,3 +316,19 @@ _rtld_thread_init(struct RtldLockInfo *pli)
thread_mask_set(flags);
dbg("_rtld_thread_init: done");
}
void
_rtld_atfork_pre(int *locks)
{
locks[2] = wlock_acquire(rtld_phdr_lock);
locks[0] = rlock_acquire(rtld_bind_lock);
}
void
_rtld_atfork_post(int *locks)
{
rlock_release(rtld_bind_lock, locks[0]);
wlock_release(rtld_phdr_lock, locks[2]);
}

2
libexec/rtld-elf/rtld_lock.h
View File

@ -44,6 +44,8 @@ struct RtldLockInfo
};
extern void _rtld_thread_init(struct RtldLockInfo *);
extern void _rtld_atfork_pre(int *);
extern void _rtld_atfork_post(int *);
#ifdef IN_RTLD