$a0 is saved across _dl_runtime_resolve(); $v0 is not. Unfortunately,
__syscall_error() uses $v0 for its argument, not $a0 as is the MIPS ABI
standard. This means that if lazy binding was used for __syscall_error(),
the errno value in $v0 could get corrupted.
The problem can be easily seen in testcases where syscalls in librt fail;
when librt tries to call __syscall_error() in libc, the argument gets
lost and errno gets set to a bogus value:
# ./tst-mqueue1 ; echo $?
mq_receive on O_WRONLY mqd_t did not fail with EBADF: Unknown error
2004684208
1
# ./tst-mqueue2 ; echo $?
mq_timedreceive with too small msg_len did not fail with EMSGSIZE: Unknown
error 1997360560
1
# ./tst-mqueue4 ; echo $?
mq_timedsend did not fail with ETIMEDOUT: Unknown error 2008747440
1
When _dl_runtime_resolve() was taken out of the equation, the same test
cases passed:
# LD_BIND_NOW=y ./tst-mqueue1 ; echo $?
0
# LD_BIND_NOW=y ./tst-mqueue2 ; echo $?
0
# LD_BIND_NOW=y ./tst-mqueue4 ; echo $?
0
Changing __syscall_error() to look at $a0 instead of $v0 fixed the
problem.
(Note that there is also a "__syscall_error.c" file which presumably
uses the standard C calling conventions, but I do not think it is used
on MIPS.)
Signed-off-by: Kevin Cernekee <cerne...@gmail.com>
---
libc/sysdeps/linux/mips/syscall_error.S | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/libc/sysdeps/linux/mips/syscall_error.S
b/libc/sysdeps/linux/mips/syscall_error.S
index 51a8efa..0cc20da 100644
--- a/libc/sysdeps/linux/mips/syscall_error.S
+++ b/libc/sysdeps/linux/mips/syscall_error.S
@@ -43,7 +43,7 @@ ENTRY(__syscall_error)
#ifdef __PIC__
SAVE_GP(GPOFF)
#endif
- REG_S v0, V0OFF(sp)
+ REG_S a0, V0OFF(sp)
REG_S ra, RAOFF(sp)
/* Find our per-thread errno address */
--
1.7.9
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