[PATCH 2/2] x86: change syscall_trace_leave() to rely on tracehook_report_syscall_exit(step)

[Oleg Nesterov]

Extract arch_fill_sigtrap_info() from send_sigtrap() and change
syscall_trace_leave() to rely on tracehook_report_syscall_exit()
to handle stepping.

Note: before this patch x86 generated the unnecessary SIGTRAP
when PTRACE_SINGLESTEP done at the syscall-exit stop, now x86
matches other architectures.

---

 arch/x86/include/asm/ptrace.h |    5 ++++
 arch/x86/kernel/ptrace.c      |   51 +++++++++++++++++++++++-------------------
 2 files changed, 33 insertions(+), 23 deletions(-)

--- TH/arch/x86/include/asm/ptrace.h~2_CONVERT_X86	2009-06-11 14:16:46.000000000 +0200
+++ TH/arch/x86/include/asm/ptrace.h	2009-11-08 20:45:21.000000000 +0100
@@ -230,6 +230,11 @@ extern void user_enable_block_step(struc
 #define arch_has_block_step()	(boot_cpu_data.x86 >= 6)
 #endif
 
+struct siginfo;
+void arch_fill_sigtrap_info(struct task_struct *tsk, struct pt_regs *regs,
+				struct siginfo *info);
+#define arch_has_fill_sigtrap_info
+
 struct user_desc;
 extern int do_get_thread_area(struct task_struct *p, int idx,
 			      struct user_desc __user *info);
--- TH/arch/x86/kernel/ptrace.c~2_CONVERT_X86	2009-09-23 21:12:01.000000000 +0200
+++ TH/arch/x86/kernel/ptrace.c	2009-11-08 20:54:26.000000000 +0100
@@ -1437,21 +1437,33 @@ const struct user_regset_view *task_user
 #endif
 }
 
-void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs,
-					 int error_code, int si_code)
+static inline void fill_sigtrap_info(struct task_struct *tsk,
+					struct pt_regs *regs,
+					int error_code, int si_code,
+					struct siginfo *info)
 {
-	struct siginfo info;
-
 	tsk->thread.trap_no = 1;
 	tsk->thread.error_code = error_code;
 
-	memset(&info, 0, sizeof(info));
-	info.si_signo = SIGTRAP;
-	info.si_code = si_code;
+	memset(info, 0, sizeof(*info));
+	info->si_signo = SIGTRAP;
+	info->si_code = si_code;
+	info->si_addr = user_mode_vm(regs) ? (void __user *) regs->ip : NULL;
+}
 
-	/* User-mode ip? */
-	info.si_addr = user_mode_vm(regs) ? (void __user *) regs->ip : NULL;
+void arch_fill_sigtrap_info(struct task_struct *tsk,
+				struct pt_regs *regs,
+				struct siginfo *info)
+{
+	fill_sigtrap_info(tsk, regs, 0, TRAP_BRKPT, info);
+}
 
+void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs,
+					 int error_code, int si_code)
+{
+	struct siginfo info;
+
+	fill_sigtrap_info(tsk, regs, error_code, si_code, &info);
 	/* Send us the fake SIGTRAP */
 	force_sig_info(SIGTRAP, &info, tsk);
 }
@@ -1516,29 +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);
 }