[summary: Get rid of libc alias __GI___errno_location]
It seems with Linuxthreads.old (yet to confirm NPTL) errno is not thread
safe.
A simple pthread linked test program (at the bottom) which makes a
failing syscall e.g. open("/not-exist") fails to observe the right errno
in the thread (main is OK)
Conceptually uClibc defines weak __errno_location() while libpthread
defines astrong variant. This arrangement shd work when using -pthread
links. The spoil sport is __GI___errno_location, intended to bypass PLT
for intra-libc callers. It gets called even in case of LT.old links
given the syscall wrappers in libpthread (LT.old). e.g.
open [ in libpthread ]
pthreadsetcanceltype()
__libc_open()
__GI__open()
...
- __GI___errno_location [ existing ]
+ __errno_location [ intended ]
....
pthreadsetcanceltype()
So the solution is to get rid of GI alias for errno_location
altogether.
I tested this on master for ARC as well as an ARMv7 buildroot LT.old
build (daily snapshot of uClibc) and fix works on both.
-------- before ------->8----------
[Main thread] Initial errno = 99
errno @b6f6c338 = 2 (OK)
[Child Thread] Initial errno = 0
errno @be1ffee8 = 0 (BROKEN)
Errno in main after child 4
------- after ----->8------------------
[Main thread] Initial errno = 99
errno @b6f9a338 = 2 (OK)
[Child Thread] Initial errno = 0
errno @be1ffee8 = 2 (OK)
Errno in main after child 4
============Test case ===================
/* $CROSS-gcc -o errno-arc -lpthread */
void *th(void *str)
{
int fd;
printf("\n[%s] Initial errno = %d\n", (char *)str, errno);
fd = open("/nothing", O_RDONLY);
if (fd >= 0) {
close(fd);
//printf("success\n");
} else
printf("errno @%x = %d (%s)\n", &errno, errno, errno ? "OK" :
"BROKEN");
errno = 66;
return NULL;
}
int main(void)
{
pthread_t t;
void *r;
int err;
errno = 99;
th("Main thread");
err = pthread_create(&t, NULL, th, "Child Thread");
if (err) {
fprintf(stderr, "could not spawn thread: %s\n", strerror(err));
return 1;
}
pthread_join(t, &r);
printf("Errno in main after child %d\n", errno);
return 0;
}
Cc: Christian Ruppert <[email protected]>
CC: Francois Bedard <[email protected]>
Cc: Joern Rennecke <[email protected]>
Cc: Jeremy Bennett <[email protected]>
Signed-off-by: Vineet Gupta <[email protected]>
---
libc/misc/internals/__errno_location.c | 1 -
libc/sysdeps/linux/common/bits/errno.h | 3 ---
2 files changed, 4 deletions(-)
diff --git a/libc/misc/internals/__errno_location.c
b/libc/misc/internals/__errno_location.c
index be7a9093efa3..9bbc2d779653 100644
--- a/libc/misc/internals/__errno_location.c
+++ b/libc/misc/internals/__errno_location.c
@@ -16,4 +16,3 @@ int *__errno_location(void)
{
return &errno;
}
-libc_hidden_weak(__errno_location)
diff --git a/libc/sysdeps/linux/common/bits/errno.h
b/libc/sysdeps/linux/common/bits/errno.h
index 777338fb1e0a..611b8359001a 100644
--- a/libc/sysdeps/linux/common/bits/errno.h
+++ b/libc/sysdeps/linux/common/bits/errno.h
@@ -43,11 +43,8 @@
/* Function to get address of global `errno' variable. */
extern int *__errno_location (void) __THROW __attribute__ ((__const__));
# ifdef _LIBC
-# if !defined(__UCLIBC_HAS_TLS__) && !defined(__UCLIBC_HAS_THREADS__)
extern int weak_const_function *__errno_location(void);
-# endif
# endif
-libc_hidden_proto(__errno_location)
# ifdef __UCLIBC_HAS_THREADS__
/* When using threads, errno is a per-thread value. */
--
1.8.3.2
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