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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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20
libc/bionic/ndk_cruft.cpp
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@@ -31,7 +31,6 @@
#include <ctype.h>
#include <inttypes.h>
#include <linux/futex.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
@@ -201,25 +200,20 @@ extern "C" int vfdprintf(int fd, const char* fmt, va_list ap) {
return vdprintf(fd, fmt, ap);
}
static 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 (syscall(__NR_futex, ftx, op, value, timeout) == 0) {
return 0;
}
int result = -errno;
errno = saved_errno;
return result;
}
#define __futex_wake __real_futex_wake
#define __futex_wait __real_futex_wait
#include "private/bionic_futex.h"
#undef __futex_wake
#undef __futex_wait
// This used to be in <sys/atomics.h>.
extern "C" int __futex_wake(volatile void* ftx, int count) {
return __futex(ftx, FUTEX_WAKE, count, NULL);
return __real_futex_wake(ftx, count);
}
// This used to be in <sys/atomics.h>.
extern "C" int __futex_wait(volatile void* ftx, int value, const struct timespec* timeout) {
return __futex(ftx, FUTEX_WAIT, value, timeout);
return __real_futex_wait(ftx, value, timeout);
}
// Unity's libmono uses this.