[IA64] enable singlestep on system call

As is pointed out in
http://www.gelato.org/community/view_linear.php?id=1_1036&from=authors&value=Ian%20Wienand#1_1039,
if single step on break instruction, the break fault has higher
priority than the single-step trap. When the break fault handler
is entered, it advances the IP by 1 instruction so break instruction
single-stepping is skipped, actually it is next instruction which
is single stepped.

This patch modifies this, it adds TIF_SINGLESTEP bit for thread
flags, and generate a fake sigtrap when single stepping break
instruction. Test case in attachment can verify this. Any comments
is welcome.

Signed-off-by: bibo, mao <bibo.mao@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/kernel/ptrace.c

@@ -1405,6 +1405,7 @@ ptrace_disable (struct task_struct *child)
 	struct ia64_psr *child_psr = ia64_psr(task_pt_regs(child));
 
 	/* make sure the single step/taken-branch trap bits are not set: */
+	clear_tsk_thread_flag(child, TIF_SINGLESTEP);
 	child_psr->ss = 0;
 	child_psr->tb = 0;
 }
@@ -1525,6 +1526,7 @@ sys_ptrace (long request, pid_t pid, unsigned long addr, unsigned long data)
 		 * Make sure the single step/taken-branch trap bits
 		 * are not set:
 		 */
+		clear_tsk_thread_flag(child, TIF_SINGLESTEP);
 		ia64_psr(pt)->ss = 0;
 		ia64_psr(pt)->tb = 0;
 
@@ -1556,6 +1558,7 @@ sys_ptrace (long request, pid_t pid, unsigned long addr, unsigned long data)
 			goto out_tsk;
 
 		clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
+		set_tsk_thread_flag(child, TIF_SINGLESTEP);
 		if (request == PTRACE_SINGLESTEP) {
 			ia64_psr(pt)->ss = 1;
 		} else {
@@ -1595,13 +1598,9 @@ sys_ptrace (long request, pid_t pid, unsigned long addr, unsigned long data)
 }
 
 
-void
+static void
 syscall_trace (void)
 {
-	if (!test_thread_flag(TIF_SYSCALL_TRACE))
-		return;
-	if (!(current->ptrace & PT_PTRACED))
-		return;
 	/*
 	 * The 0x80 provides a way for the tracing parent to
 	 * distinguish between a syscall stop and SIGTRAP delivery.
@@ -1664,7 +1663,8 @@ syscall_trace_leave (long arg0, long arg1, long arg2, long arg3,
 		audit_syscall_exit(success, result);
 	}
 
-	if (test_thread_flag(TIF_SYSCALL_TRACE)
+	if ((test_thread_flag(TIF_SYSCALL_TRACE)
+	    || test_thread_flag(TIF_SINGLESTEP))
 	    && (current->ptrace & PT_PTRACED))
 		syscall_trace();
 }

include/asm-ia64/thread_info.h

@@ -84,6 +84,7 @@ struct thread_info {
 #define TIF_NEED_RESCHED	2	/* rescheduling necessary */
 #define TIF_SYSCALL_TRACE	3	/* syscall trace active */
 #define TIF_SYSCALL_AUDIT	4	/* syscall auditing active */
+#define TIF_SINGLESTEP		5	/* restore singlestep on return to user mode */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		17
 #define TIF_MCA_INIT		18	/* this task is processing MCA or INIT */
@@ -92,7 +93,8 @@ struct thread_info {
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
-#define _TIF_SYSCALL_TRACEAUDIT	(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT)
+#define _TIF_SINGLESTEP		(1 << TIF_SINGLESTEP)
+#define _TIF_SYSCALL_TRACEAUDIT	(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SINGLESTEP)
 #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)