[RFC,PATCH 07/14] ptrace: x86: change syscall_trace_leave() to rely on tracehook when stepping

[Oleg Nesterov]

(already in mm: 
ptrace-x86-change-syscall_trace_leave-to-rely-on-tracehook-when-stepping.patch)

Suggested by Roland.

Unlike powepc, x86 always calls tracehook_report_syscall_exit(step)
with step = 0, and sends the trap by hand.

This results in unnecessary SIGTRAP when PTRACE_SINGLESTEP follows
the syscall-exit stop.

Change syscall_trace_leave() to pass the correct "step" argument to
tracehook and remove the send_sigtrap() logic.

Signed-off-by: Oleg Nesterov <o...@redhat.com>
Acked-by: Roland McGrath <rol...@redhat.com>
---

 arch/x86/kernel/ptrace.c |   21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

--- V1/arch/x86/kernel/ptrace.c~7_X86_CONVERT_SYSCALL_LEAVE     2009-11-24 
19:52:11.000000000 +0100
+++ V1/arch/x86/kernel/ptrace.c 2009-11-24 19:52:12.000000000 +0100
@@ -1528,29 +1528,22 @@ asmregparm long syscall_trace_enter(stru
 
 asmregparm void syscall_trace_leave(struct pt_regs *regs)
 {
+       bool step;
+
        if (unlikely(current->audit_context))
                audit_syscall_exit(AUDITSC_RESULT(regs->ax), regs->ax);
 
        if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
                trace_sys_exit(regs, regs->ax);
 
-       if (test_thread_flag(TIF_SYSCALL_TRACE))
-               tracehook_report_syscall_exit(regs, 0);
-
        /*
         * If TIF_SYSCALL_EMU is set, we only get here because of
         * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
         * We already reported this syscall instruction in
-        * syscall_trace_enter(), so don't do any more now.
-        */
-       if (unlikely(test_thread_flag(TIF_SYSCALL_EMU)))
-               return;
-
-       /*
-        * If we are single-stepping, synthesize a trap to follow the
-        * system call instruction.
+        * syscall_trace_enter().
         */
-       if (test_thread_flag(TIF_SINGLESTEP) &&
-           tracehook_consider_fatal_signal(current, SIGTRAP))
-               send_sigtrap(current, regs, 0, TRAP_BRKPT);
+       step = unlikely(test_thread_flag(TIF_SINGLESTEP)) &&
+                       !test_thread_flag(TIF_SYSCALL_EMU);
+       if (step || test_thread_flag(TIF_SYSCALL_TRACE))
+               tracehook_report_syscall_exit(regs, step);
 }