MIPS: Negate error syscall return in trace

The sys_exit trace event takes a single return value for the system
call, which MIPS passes the value of the $v0 (result) register, however
MIPS returns positive error codes in $v0 with $a3 specifying that $v0
contains an error code. As a result erroring system calls are traced
returning positive error numbers that can't always be distinguished from
success.

Use regs_return_value() to negate the error code if $a3 is set.

Fixes: 1d7bf993e073 ("MIPS: ftrace: Add support for syscall tracepoints.")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: linux-mips@linux-mips.org
Cc: <stable@vger.kernel.org> # 3.13+
Patchwork: https://patchwork.linux-mips.org/patch/16651/
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

diff --git a/arch/mips/kernel/ptrace.c b/arch/mips/kernel/ptrace.c
index ba3b1f771256f763ce6d03143a3c6cef052ac08c..8e2ea86dc23e89896847b8ff7f60c4eeb49f1d77 100644 (file)
--- a/arch/mips/kernel/ptrace.c
+++ b/arch/mips/kernel/ptrace.c
@@ -913,7 +913,7 @@ asmlinkage void syscall_trace_leave(struct pt_regs *regs)
        audit_syscall_exit(regs);
 
        if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
-               trace_sys_exit(regs, regs->regs[2]);
+               trace_sys_exit(regs, regs_return_value(regs));
 
        if (test_thread_flag(TIF_SYSCALL_TRACE))
                tracehook_report_syscall_exit(regs, 0);