xtensa: call do_syscall_trace_{enter,leave} selectively

Check whether calls to do_syscall_trace_{enter,leave} are necessary in
the system_call function. Define _TIF_WORK_MASK to a bitmask of flags
that reuire the calls. Fix comment.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/include/asm/thread_info.h

@@ -101,8 +101,6 @@ static inline struct thread_info *current_thread_info(void)
 /*
  * thread information flags
  * - these are process state flags that various assembly files may need to access
- * - pending work-to-be-done flags are in LSW
- * - other flags in MSW
  */
 #define TIF_SYSCALL_TRACE	0	/* syscall trace active */
 #define TIF_SIGPENDING		1	/* signal pending */
@@ -118,8 +116,7 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
 
-#define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */
-#define _TIF_ALLWORK_MASK	0x0000FFFF	/* work to do on any return to u-space */
+#define _TIF_WORK_MASK		(_TIF_SYSCALL_TRACE | _TIF_SINGLESTEP)
 
 /*
  * Thread-synchronous status.

arch/xtensa/kernel/entry.S

@@ -1846,20 +1846,28 @@ ENTRY(system_call)
 
 	/* regs->syscall = regs->areg[2] */
 
-	l32i	a3, a2, PT_AREG2
+	l32i	a7, a2, PT_AREG2
+	s32i	a7, a2, PT_SYSCALL
+
+	GET_THREAD_INFO(a4, a1)
+	l32i	a3, a4, TI_FLAGS
+	movi	a4, _TIF_WORK_MASK
+	and	a3, a3, a4
+	beqz	a3, 1f
+
 	mov	a6, a2
-	s32i	a3, a2, PT_SYSCALL
 	call4	do_syscall_trace_enter
-	mov	a3, a6
+	l32i	a7, a2, PT_SYSCALL
 
+1:
 	/* syscall = sys_call_table[syscall_nr] */
 
 	movi	a4, sys_call_table
 	movi	a5, __NR_syscalls
 	movi	a6, -ENOSYS
-	bgeu	a3, a5, 1f
+	bgeu	a7, a5, 1f
 
-	addx4	a4, a3, a4
+	addx4	a4, a7, a4
 	l32i	a4, a4, 0
 	movi	a5, sys_ni_syscall;
 	beq	a4, a5, 1f
@@ -1881,6 +1889,10 @@ ENTRY(system_call)
 1:	/* regs->areg[2] = return_value */
 
 	s32i	a6, a2, PT_AREG2
+	bnez	a3, 1f
+	retw
+
+1:
 	mov	a6, a2
 	call4	do_syscall_trace_leave
 	retw

arch/xtensa/kernel/ptrace.c

@@ -487,13 +487,12 @@ long arch_ptrace(struct task_struct *child, long request,
 	return ret;
 }
 
-unsigned long do_syscall_trace_enter(struct pt_regs *regs)
+void do_syscall_trace_enter(struct pt_regs *regs)
 {
 	if (test_thread_flag(TIF_SYSCALL_TRACE) &&
 	    tracehook_report_syscall_entry(regs))
-		return NO_SYSCALL;
+		regs->syscall = NO_SYSCALL;
 
-	return regs->areg[2];
 }
 
 void do_syscall_trace_leave(struct pt_regs *regs)