linux-kernel - [Patch] ia64 enable singlestep on system call

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Message-ID: <45C06667.9080904@intel.com>
Date:	Wed, 31 Jan 2007 17:50:31 +0800
From:	"bibo,mao" <bibo.mao@...el.com>
To:	linux-ia64@...r.kernel.org
CC:	linux-kernel@...r.kernel.org, "Luck, Tony" <tony.luck@...el.com>,
	Roland McGrath <roland@...hat.com>,
	"Keshavamurthy, Anil S" <anil.s.keshavamurthy@...el.com>
Subject: [Patch] ia64 enable singlestep on system call

hi,
 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@...el.com>

thanks
bibo,mao 

--------------------------------------------------------
 arch/ia64/kernel/ptrace.c      |   12 ++++++------
 include/asm-ia64/thread_info.h |    4 +++-
 2 files changed, 9 insertions(+), 7 deletions(-)

diff -Nrup -X /root/dontdiff 2.6.20-rc6.org/arch/ia64/kernel/ptrace.c 2.6.20-rc6/arch/ia64/kernel/ptrace.c
--- 2.6.20-rc6.org/arch/ia64/kernel/ptrace.c	2006-09-25 15:20:42.000000000 +0800
+++ 2.6.20-rc6/arch/ia64/kernel/ptrace.c	2007-01-31 18:04:45.000000000 +0800
@@ -1405,6 +1405,7 @@ ptrace_disable (struct task_struct *chil
 	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, uns
 		 * 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, uns
 			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, uns
 }
 
 
-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 arg
 		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();
 }
diff -Nrup -X /root/dontdiff 2.6.20-rc6.org/include/asm-ia64/thread_info.h 2.6.20-rc6/include/asm-ia64/thread_info.h
--- 2.6.20-rc6.org/include/asm-ia64/thread_info.h	2007-01-30 17:57:16.000000000 +0800
+++ 2.6.20-rc6/include/asm-ia64/thread_info.h	2007-01-31 18:01:48.000000000 +0800
@@ -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)

View attachment "singlestep.c" of type "text/plain" (2432 bytes)