[PATCH] ppc64: fix single-stepping into/out of signal handlers

This is the second of 3 patches from David Woodhouse which fix various
problems with signal handling on ppc64.

The problem that this patch fixes is that a process being single-stepped
will execute one instruction too many in certain cases: when a signal is
delivered, when a signal handler returns, and when a system call
instruction is single-stepped.  This patch fixes it by checking if the
process is being single-stepped in the syscall exit path and on signal
delivery, and stopping it if so.  To avoid slowing down the syscall exit
path in the normal case, we use a bit in the thread_info flags, which can
be tested along with the other bits we already test in the syscall exit
path.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/ppc64/kernel/entry.S

@@ -162,7 +162,7 @@ syscall_error_cont:
 
 	/* check for syscall tracing or audit */
 	ld	r9,TI_FLAGS(r12)
-	andi.	r0,r9,_TIF_SYSCALL_T_OR_A
+	andi.	r0,r9,(_TIF_SYSCALL_T_OR_A|_TIF_SINGLESTEP)
 	bne-	syscall_exit_trace
 syscall_exit_trace_cont:
 
@@ -322,7 +322,7 @@ _GLOBAL(ppc64_rt_sigreturn)
 	blt	syscall_exit
 	clrrdi	r4,r1,THREAD_SHIFT
 	ld	r4,TI_FLAGS(r4)
-	andi.	r4,r4,_TIF_SYSCALL_T_OR_A
+	andi.	r4,r4,(_TIF_SYSCALL_T_OR_A|_TIF_SINGLESTEP)
 	beq+	81f
 	bl	.do_syscall_trace_leave
 81:	b	.ret_from_except

arch/ppc64/kernel/ptrace.c

@@ -318,7 +318,8 @@ void do_syscall_trace_leave(void)
 	if (unlikely(current->audit_context))
 		audit_syscall_exit(current, 0);	/* FIXME: pass pt_regs */
 
-	if (test_thread_flag(TIF_SYSCALL_TRACE)
+	if ((test_thread_flag(TIF_SYSCALL_TRACE)
+	     || test_thread_flag(TIF_SINGLESTEP))
 	    && (current->ptrace & PT_PTRACED))
 		do_syscall_trace();
 }

arch/ppc64/kernel/signal.c

@@ -26,6 +26,7 @@
 #include <linux/unistd.h>
 #include <linux/stddef.h>
 #include <linux/elf.h>
+#include <linux/ptrace.h>
 #include <asm/sigcontext.h>
 #include <asm/ucontext.h>
 #include <asm/uaccess.h>
@@ -452,6 +453,9 @@ static void setup_rt_frame(int signr, struct k_sigaction *ka, siginfo_t *info,
 	if (err)
 		goto badframe;
 
+	if (test_thread_flag(TIF_SINGLESTEP))
+		ptrace_notify(SIGTRAP);
+
 	return;
 
 badframe:

arch/ppc64/kernel/signal32.c

@@ -25,6 +25,7 @@
 #include <linux/errno.h>
 #include <linux/elf.h>
 #include <linux/compat.h>
+#include <linux/ptrace.h>
 #include <asm/ppc32.h>
 #include <asm/uaccess.h>
 #include <asm/ppcdebug.h>
@@ -700,6 +701,9 @@ static void handle_rt_signal32(unsigned long sig, struct k_sigaction *ka,
 	regs->trap = 0;
 	regs->result = 0;
 
+	if (test_thread_flag(TIF_SINGLESTEP))
+		ptrace_notify(SIGTRAP);
+
 	return;
 
 badframe:
@@ -863,6 +867,9 @@ static void handle_signal32(unsigned long sig, struct k_sigaction *ka,
 	regs->trap = 0;
 	regs->result = 0;
 
+	if (test_thread_flag(TIF_SINGLESTEP))
+		ptrace_notify(SIGTRAP);
+
 	return;
 
 badframe:

include/asm-ppc64/ptrace-common.h

@@ -58,6 +58,7 @@ static inline void set_single_step(struct task_struct *task)
 	struct pt_regs *regs = task->thread.regs;
 	if (regs != NULL)
 		regs->msr |= MSR_SE;
+	set_ti_thread_flag(task->thread_info, TIF_SINGLESTEP);
 }
 
 static inline void clear_single_step(struct task_struct *task)
@@ -65,6 +66,7 @@ static inline void clear_single_step(struct task_struct *task)
 	struct pt_regs *regs = task->thread.regs;
 	if (regs != NULL)
 		regs->msr &= ~MSR_SE;
+	clear_ti_thread_flag(task->thread_info, TIF_SINGLESTEP);
 }
 
 #endif /* _PPC64_PTRACE_COMMON_H */

include/asm-ppc64/thread_info.h

@@ -97,6 +97,7 @@ static inline struct thread_info *current_thread_info(void)
 #define TIF_RUN_LIGHT		6	/* iSeries run light */
 #define TIF_ABI_PENDING		7	/* 32/64 bit switch needed */
 #define TIF_SYSCALL_AUDIT	8	/* syscall auditing active */
+#define TIF_SINGLESTEP		9	/* singlestepping active */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
@@ -108,6 +109,7 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_RUN_LIGHT		(1<<TIF_RUN_LIGHT)
 #define _TIF_ABI_PENDING	(1<<TIF_ABI_PENDING)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
+#define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
 #define _TIF_SYSCALL_T_OR_A	(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT)
 
 #define _TIF_USER_WORK_MASK	(_TIF_NOTIFY_RESUME | _TIF_SIGPENDING | \