MIPS: Use $a0 instead of $v0 for __syscall_error() argument

$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 <cernekee@gmail.com>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

0 files changed, 0 insertions, 0 deletions