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    Subject[PATCH 4.9 081/125] MIPS: Negate error syscall return in trace
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: James Hogan <james.hogan@imgtec.com>

    commit 4f32a39d49b25eaa66d2420f1f03d371ea4cd906 upstream.

    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
    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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/mips/kernel/ptrace.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/arch/mips/kernel/ptrace.c
    +++ b/arch/mips/kernel/ptrace.c
    @@ -924,7 +924,7 @@ asmlinkage void syscall_trace_leave(stru
    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);

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