x86: common send_sigtrap helper for debug event SIGTRAP's,

and use that for system call single-step events.

This one also gets the user mode test right, and makes sure
the siginfo is not leaking any stack contents.

arch/i386/kernel/ptrace.c

@@ -553,6 +553,24 @@ asmlinkage int sys_ptrace(long request, long pid, long addr, long data)
 	return ret;
 }
 
+void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs, int error_code)
+{
+	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 = TRAP_BRKPT;
+
+	/* User-mode eip? */
+	info.si_addr = user_mode(regs) ? (void __user *) regs->eip : NULL;
+
+	/* Send us the fakey SIGTRAP */
+	force_sig_info(SIGTRAP, &info, tsk);
+}
+
 /* notification of system call entry/exit
  * - triggered by current->work.syscall_trace
  */
@@ -568,15 +586,19 @@ void do_syscall_trace(struct pt_regs *regs, int entryexit)
 			audit_syscall_exit(current, regs->eax);
 	}
 
-	if (!test_thread_flag(TIF_SYSCALL_TRACE) &&
-	    !test_thread_flag(TIF_SINGLESTEP))
-		return;
 	if (!(current->ptrace & PT_PTRACED))
 		return;
+
+	/* Fake a debug trap */
+	if (test_thread_flag(TIF_SINGLESTEP))
+		send_sigtrap(current, regs, 0);
+
+	if (!test_thread_flag(TIF_SYSCALL_TRACE))
+		return;
+
 	/* the 0x80 provides a way for the tracing parent to distinguish
 	   between a syscall stop and SIGTRAP delivery */
-	ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD) &&
-				 !test_thread_flag(TIF_SINGLESTEP) ? 0x80 : 0));
+	ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD) ? 0x80 : 0));
 
 	/*
 	 * this isn't the same as continuing with a signal, but it will do

arch/i386/kernel/traps.c

@@ -682,7 +682,6 @@ fastcall void do_debug(struct pt_regs * regs, long error_code)
 {
 	unsigned int condition;
 	struct task_struct *tsk = current;
-	siginfo_t info;
 
 	__asm__ __volatile__("movl %%db6,%0" : "=r" (condition));
 
@@ -723,18 +722,7 @@ fastcall void do_debug(struct pt_regs * regs, long error_code)
 	}
 
 	/* Ok, finally something we can handle */
-	tsk->thread.trap_no = 1;
-	tsk->thread.error_code = error_code;
-	info.si_signo = SIGTRAP;
-	info.si_errno = 0;
-	info.si_code = TRAP_BRKPT;
-	
-	/* If this is a kernel mode trap, save the user PC on entry to 
-	 * the kernel, that's what the debugger can make sense of.
-	 */
-	info.si_addr = ((regs->xcs & 3) == 0) ? (void __user *)tsk->thread.eip
-	                                      : (void __user *)regs->eip;
-	force_sig_info(SIGTRAP, &info, tsk);
+	send_sigtrap(tsk, regs, error_code);
 
 	/* Disable additional traps. They'll be re-enabled when
 	 * the signal is delivered.

include/asm-i386/ptrace.h

@@ -55,6 +55,8 @@ struct pt_regs {
 #define PTRACE_SET_THREAD_AREA    26
 
 #ifdef __KERNEL__
+struct task_struct;
+extern void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs, int error_code);
 #define user_mode(regs) ((VM_MASK & (regs)->eflags) || (3 & (regs)->xcs))
 #define instruction_pointer(regs) ((regs)->eip)
 #if defined(CONFIG_SMP) && defined(CONFIG_FRAME_POINTER)