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Revert "Revert "Lose the hand-written futex assembler.""

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The problem with the original patch was that using syscall(3) means that
errno can be set, but pthread_create(3) was abusing the TLS errno slot as
a pthread_mutex_t for the thread startup handshake.

There was also a mistake in the check for syscall failures --- it should
have checked against -1 instead of 0 (not just because that's the default
idiom, but also here because futex(2) can legitimately return values > 0).

This patch stops abusing the TLS errno slot and adds a pthread_mutex_t to
pthread_internal_t instead. (Note that for LP64 sizeof(pthread_mutex_t) >
sizeof(uintptr_t), so we could potentially clobber other TLS slots too.)

I've also rewritten the LP32 compatibility stubs to directly reuse the
code from the .h file.

This reverts commit 75c55ff84e.

Bug: 15195455
Change-Id: I6ffb13e5cf6a35d8f59f692d94192aae9ab4593d
This commit is contained in:
Elliott Hughes
2014-05-28 19:35:33 +00:00
parent 52f74322b1
commit b30aff405a
24 changed files with 45 additions and 455 deletions
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23
libc/private/bionic_futex.h
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@@ -28,31 +28,42 @@
#ifndef _BIONIC_FUTEX_H
#define _BIONIC_FUTEX_H
#include <errno.h>
#include <linux/futex.h>
#include <sys/cdefs.h>
#include <stdbool.h>
#include <stddef.h>
#include <sys/cdefs.h>
#include <sys/syscall.h>
__BEGIN_DECLS
struct timespec;
extern int __futex_syscall4(volatile void* ftx, int op, int value, const struct timespec* timeout);
static inline __always_inline int __futex(volatile void* ftx, int op, int value, const struct timespec* timeout) {
// Our generated syscall assembler sets errno, but our callers (pthread functions) don't want to.
int saved_errno = errno;
if (__predict_false(syscall(__NR_futex, ftx, op, value, timeout) == -1)) {
int result = -errno;
errno = saved_errno;
return result;
}
return 0;
}
static inline int __futex_wake(volatile void* ftx, int count) {
return __futex_syscall4(ftx, FUTEX_WAKE, count, NULL);
return __futex(ftx, FUTEX_WAKE, count, NULL);
}
static inline int __futex_wake_ex(volatile void* ftx, bool shared, int count) {
return __futex_syscall4(ftx, shared ? FUTEX_WAKE : FUTEX_WAKE_PRIVATE, count, NULL);
return __futex(ftx, shared ? FUTEX_WAKE : FUTEX_WAKE_PRIVATE, count, NULL);
}
static inline int __futex_wait(volatile void* ftx, int value, const struct timespec* timeout) {
return __futex_syscall4(ftx, FUTEX_WAIT, value, timeout);
return __futex(ftx, FUTEX_WAIT, value, timeout);
}
static inline int __futex_wait_ex(volatile void* ftx, bool shared, int value, const struct timespec* timeout) {
return __futex_syscall4(ftx, shared ? FUTEX_WAIT : FUTEX_WAIT_PRIVATE, value, timeout);
return __futex(ftx, shared ? FUTEX_WAIT : FUTEX_WAIT_PRIVATE, value, timeout);
}
__END_DECLS