powerpc: Fix various syscall/signal/swapcontext bugs

A careful reading of the recent changes to the system call entry/exit
paths revealed several problems, plus some things that could be
simplified and improved:

* 32-bit wasn't testing the _TIF_NOERROR bit in the syscall fast exit
  path, so it was only doing anything with it once it saw some other
  bit being set.  In other words, the noerror behaviour would apply to
  the next system call where we had to reschedule or deliver a signal,
  which is not necessarily the current system call.

* 32-bit wasn't doing the call to ptrace_notify in the syscall exit
  path when the _TIF_SINGLESTEP bit was set.

* _TIF_RESTOREALL was in both _TIF_USER_WORK_MASK and
  _TIF_PERSYSCALL_MASK, which is odd since _TIF_RESTOREALL is only set
  by system calls.  I took it out of _TIF_USER_WORK_MASK.

* On 64-bit, _TIF_RESTOREALL wasn't causing the non-volatile registers
  to be restored (unless perhaps a signal was delivered or the syscall
  was traced or single-stepped).  Thus the non-volatile registers
  weren't restored on exit from a signal handler.  We probably got
  away with it mostly because signal handlers written in C wouldn't
  alter the non-volatile registers.

* On 32-bit I simplified the code and made it more like 64-bit by
  making the syscall exit path jump to ret_from_except to handle
  preemption and signal delivery.

* 32-bit was calling do_signal unnecessarily when _TIF_RESTOREALL was
  set - but I think because of that 32-bit was actually restoring the
  non-volatile registers on exit from a signal handler.

* I changed the order of enabling interrupts and saving the
  non-volatile registers before calling do_syscall_trace_leave; now we
  enable interrupts first.

Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/entry_32.S

@@ -227,7 +227,7 @@ ret_from_syscall:
 	MTMSRD(r10)
 	lwz	r9,TI_FLAGS(r12)
 	li	r8,-_LAST_ERRNO
-	andi.	r0,r9,(_TIF_SYSCALL_T_OR_A|_TIF_SIGPENDING|_TIF_NEED_RESCHED|_TIF_RESTOREALL|_TIF_RESTORE_SIGMASK)
+	andi.	r0,r9,(_TIF_SYSCALL_T_OR_A|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK)
 	bne-	syscall_exit_work
 	cmplw	0,r3,r8
 	blt+	syscall_exit_cont
@@ -287,8 +287,10 @@ syscall_dotrace:
 
 syscall_exit_work:
 	andi.	r0,r9,_TIF_RESTOREALL
-	bne-	2f
-	cmplw	0,r3,r8
+	beq+	0f
+	REST_NVGPRS(r1)
+	b	2f
+0:	cmplw	0,r3,r8
 	blt+	1f
 	andi.	r0,r9,_TIF_NOERROR
 	bne-	1f
@@ -302,9 +304,7 @@ syscall_exit_work:
 2:	andi.	r0,r9,(_TIF_PERSYSCALL_MASK)
 	beq	4f
 
-	/* Clear per-syscall TIF flags if any are set, but _leave_
-	_TIF_SAVE_NVGPRS set in r9 since we haven't dealt with that
-	yet.  */
+	/* Clear per-syscall TIF flags if any are set.  */
 
 	li	r11,_TIF_PERSYSCALL_MASK
 	addi	r12,r12,TI_FLAGS
@@ -318,8 +318,13 @@ syscall_exit_work:
 	subi	r12,r12,TI_FLAGS
 	
 4:	/* Anything which requires enabling interrupts? */
-	andi.	r0,r9,(_TIF_SYSCALL_T_OR_A|_TIF_SINGLESTEP|_TIF_SAVE_NVGPRS)
-	beq	7f
+	andi.	r0,r9,(_TIF_SYSCALL_T_OR_A|_TIF_SINGLESTEP)
+	beq	ret_from_except
+
+	/* Re-enable interrupts */
+	ori	r10,r10,MSR_EE
+	SYNC
+	MTMSRD(r10)
 
 	/* Save NVGPRS if they're not saved already */
 	lwz	r4,_TRAP(r1)
@@ -328,71 +333,11 @@ syscall_exit_work:
 	SAVE_NVGPRS(r1)
 	li	r4,0xc00
 	stw	r4,_TRAP(r1)
-
-	/* Re-enable interrupts */
-5:	ori	r10,r10,MSR_EE
-	SYNC
-	MTMSRD(r10)
-
-	andi.	r0,r9,_TIF_SAVE_NVGPRS
-	bne	save_user_nvgprs
-
-save_user_nvgprs_cont:
-	andi.	r0,r9,(_TIF_SYSCALL_T_OR_A|_TIF_SINGLESTEP)
-	beq	7f
-
+5:
 	addi	r3,r1,STACK_FRAME_OVERHEAD
 	bl	do_syscall_trace_leave
-	REST_NVGPRS(r1)
+	b	ret_from_except_full
 
-6:	lwz	r3,GPR3(r1)
-	LOAD_MSR_KERNEL(r10,MSR_KERNEL)	/* doesn't include MSR_EE */
-	SYNC
-	MTMSRD(r10)		/* disable interrupts again */
-	rlwinm	r12,r1,0,0,(31-THREAD_SHIFT)	/* current_thread_info() */
-	lwz	r9,TI_FLAGS(r12)
-7:
-	andi.	r0,r9,_TIF_NEED_RESCHED
-	bne	8f
-	lwz	r5,_MSR(r1)
-	andi.	r5,r5,MSR_PR
-	beq	ret_from_except
-	andi.	r0,r9,_TIF_SIGPENDING|_TIF_RESTORE_SIGMASK
-	beq	ret_from_except
-	b	do_user_signal
-8:
-	ori	r10,r10,MSR_EE
-	SYNC
-	MTMSRD(r10)		/* re-enable interrupts */
-	bl	schedule
-	b	6b
-
-save_user_nvgprs:
-	lwz	r8,TI_SIGFRAME(r12)
-
-.macro savewords start, end
-  1:	stw \start,4*(\start)(r8)
-	.section __ex_table,"a"
-	.align	2
-	.long	1b,save_user_nvgprs_fault
-	.previous
-	.if \end - \start
-	savewords "(\start+1)",\end
-	.endif
-.endm	
-	savewords 14,31
-	b	save_user_nvgprs_cont
-
-	
-save_user_nvgprs_fault:
-	li	r3,11		/* SIGSEGV */
-	lwz	r4,TI_TASK(r12)
-	bl	force_sigsegv
-
-	rlwinm	r12,r1,0,0,(31-THREAD_SHIFT)	/* current_thread_info() */
-	lwz	r9,TI_FLAGS(r12)
-	b	save_user_nvgprs_cont
-	
 #ifdef SHOW_SYSCALLS
 do_show_syscall:
 #ifdef SHOW_SYSCALLS_TASK
@@ -490,6 +435,14 @@ ppc_clone:
 	stw	r0,_TRAP(r1)		/* register set saved */
 	b	sys_clone
 
+	.globl	ppc_swapcontext
+ppc_swapcontext:
+	SAVE_NVGPRS(r1)
+	lwz	r0,_TRAP(r1)
+	rlwinm	r0,r0,0,0,30		/* clear LSB to indicate full */
+	stw	r0,_TRAP(r1)		/* register set saved */
+	b	sys_swapcontext
+
 /*
  * Top-level page fault handling.
  * This is in assembler because if do_page_fault tells us that
@@ -683,7 +636,7 @@ user_exc_return:		/* r10 contains MSR_KERNEL here */
 	/* Check current_thread_info()->flags */
 	rlwinm	r9,r1,0,0,(31-THREAD_SHIFT)
 	lwz	r9,TI_FLAGS(r9)
-	andi.	r0,r9,(_TIF_SIGPENDING|_TIF_NEED_RESCHED|_TIF_RESTOREALL|_TIF_RESTORE_SIGMASK)
+	andi.	r0,r9,(_TIF_SIGPENDING|_TIF_RESTORE_SIGMASK|_TIF_NEED_RESCHED)
 	bne	do_work
 
 restore_user: