openrisc: Rework signal handling

The mainline signal handling code for OpenRISC has been buggy since day
one with respect to syscall restart.  This patch significantly reworks
the signal handling code:

i)   Move the "work pending" loop to C code (borrowed from ARM arch)

ii)  Allow a tracer to muck about with the IP and skip syscall restart
     in that case (again, borrowed from ARM)

iii) Make signal handling WRT syscall restart actually work

v)   Make the signal handling code look more like that of other
     architectures so that it's easier for others to follow
Reported-by: Anders Nystrom <anders@southpole.se>
Signed-off-by: Jonas Bonn <jonas@southpole.se>

arch/openrisc/kernel/entry.S

@@ -853,37 +853,44 @@ UNHANDLED_EXCEPTION(_vector_0x1f00,0x1f00)
 
 /* ========================================================[ return ] === */
 
+_resume_userspace:
+	DISABLE_INTERRUPTS(r3,r4)
+	l.lwz	r4,TI_FLAGS(r10)
+	l.andi	r13,r4,_TIF_WORK_MASK
+	l.sfeqi	r13,0
+	l.bf	_restore_all
+	 l.nop
+
 _work_pending:
-	/*
-	 * if (current_thread_info->flags & _TIF_NEED_RESCHED)
-	 *     schedule();
-	 */
-	l.lwz   r5,TI_FLAGS(r10)
-	l.andi	r3,r5,_TIF_NEED_RESCHED
-	l.sfnei r3,0
-	l.bnf   _work_notifysig
+	l.lwz	r5,PT_ORIG_GPR11(r1)
+	l.sfltsi r5,0
+	l.bnf	1f
 	 l.nop
-	l.jal   schedule
+	l.andi	r5,r5,0
+1:
+	l.jal	do_work_pending
+	 l.ori	r3,r1,0			/* pt_regs */
+
+	l.sfeqi	r11,0
+	l.bf	_restore_all
 	 l.nop
-	l.j	_resume_userspace
+	l.sfltsi r11,0
+	l.bnf	1f
 	 l.nop
-
-/* Handle pending signals and notify-resume requests.
- * do_notify_resume must be passed the latest pushed pt_regs, not
- * necessarily the "userspace" ones.  Also, pt_regs->syscallno
- * must be set so that the syscall restart functionality works.
- */
-_work_notifysig:
-	l.jal	do_notify_resume
-	 l.ori	r3,r1,0		  /* pt_regs */
-
-_resume_userspace:
-	DISABLE_INTERRUPTS(r3,r4)
-	l.lwz	r3,TI_FLAGS(r10)
-	l.andi	r3,r3,_TIF_WORK_MASK
-	l.sfnei	r3,0
-	l.bf	_work_pending
+	l.and	r11,r11,r0
+	l.ori	r11,r11,__NR_restart_syscall
+	l.j	_syscall_check_trace_enter
 	 l.nop
+1:
+	l.lwz	r11,PT_ORIG_GPR11(r1)
+	/* Restore arg registers */
+	l.lwz	r3,PT_GPR3(r1)
+	l.lwz	r4,PT_GPR4(r1)
+	l.lwz	r5,PT_GPR5(r1)
+	l.lwz	r6,PT_GPR6(r1)
+	l.lwz	r7,PT_GPR7(r1)
+	l.j	_syscall_check_trace_enter
+	 l.lwz	r8,PT_GPR8(r1)
 
 _restore_all:
 	RESTORE_ALL

arch/openrisc/kernel/signal.c

@@ -28,24 +28,24 @@
 #include <linux/tracehook.h>
 
 #include <asm/processor.h>
+#include <asm/syscall.h>
 #include <asm/ucontext.h>
 #include <asm/uaccess.h>
 
 #define DEBUG_SIG 0
 
 struct rt_sigframe {
-	struct siginfo *pinfo;
-	void *puc;
 	struct siginfo info;
 	struct ucontext uc;
 	unsigned char retcode[16];	/* trampoline code */
 };
 
-static int restore_sigcontext(struct pt_regs *regs, struct sigcontext *sc)
+static int restore_sigcontext(struct pt_regs *regs,
+			      struct sigcontext __user *sc)
 {
-	unsigned int err = 0;
+	int err = 0;
 
-	/* Alwys make any pending restarted system call return -EINTR */
+	/* Always make any pending restarted system calls return -EINTR */
 	current_thread_info()->restart_block.fn = do_no_restart_syscall;
 
 	/*
@@ -53,25 +53,21 @@ static int restore_sigcontext(struct pt_regs *regs, struct sigcontext *sc)
 	 * (sc is already checked for VERIFY_READ since the sigframe was
 	 *  checked in sys_sigreturn previously)
 	 */
-	if (__copy_from_user(regs, sc->regs.gpr, 32 * sizeof(unsigned long)))
-		goto badframe;
-	if (__copy_from_user(&regs->pc, &sc->regs.pc, sizeof(unsigned long)))
-		goto badframe;
-	if (__copy_from_user(&regs->sr, &sc->regs.sr, sizeof(unsigned long)))
-		goto badframe;
+	err |= __copy_from_user(regs, sc->regs.gpr, 32 * sizeof(unsigned long));
+	err |= __copy_from_user(&regs->pc, &sc->regs.pc, sizeof(unsigned long));
+	err |= __copy_from_user(&regs->sr, &sc->regs.sr, sizeof(unsigned long));
 
 	/* make sure the SM-bit is cleared so user-mode cannot fool us */
 	regs->sr &= ~SPR_SR_SM;
 
+	regs->orig_gpr11 = -1;	/* Avoid syscall restart checks */
+
 	/* TODO: the other ports use regs->orig_XX to disable syscall checks
 	 * after this completes, but we don't use that mechanism. maybe we can
 	 * use it now ?
 	 */
 
 	return err;
-
-badframe:
-	return 1;
 }
 
 asmlinkage long _sys_rt_sigreturn(struct pt_regs *regs)
@@ -111,21 +107,18 @@ asmlinkage long _sys_rt_sigreturn(struct pt_regs *regs)
  * Set up a signal frame.
  */
 
-static int setup_sigcontext(struct sigcontext *sc, struct pt_regs *regs,
-			    unsigned long mask)
+static int setup_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc)
 {
 	int err = 0;
 
 	/* copy the regs */
-
+	/* There should be no need to save callee-saved registers here...
+	 * ...but we save them anyway.  Revisit this
+	 */
 	err |= __copy_to_user(sc->regs.gpr, regs, 32 * sizeof(unsigned long));
 	err |= __copy_to_user(&sc->regs.pc, &regs->pc, sizeof(unsigned long));
 	err |= __copy_to_user(&sc->regs.sr, &regs->sr, sizeof(unsigned long));
 
-	/* then some other stuff */
-
-	err |= __put_user(mask, &sc->oldmask);
-
 	return err;
 }
 
@@ -181,24 +174,18 @@ static int setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
 	int err = 0;
 
 	frame = get_sigframe(ka, regs, sizeof(*frame));
-
 	if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
 		goto give_sigsegv;
 
-	err |= __put_user(&frame->info, &frame->pinfo);
-	err |= __put_user(&frame->uc, &frame->puc);
-
+	/* Create siginfo.  */
 	if (ka->sa.sa_flags & SA_SIGINFO)
 		err |= copy_siginfo_to_user(&frame->info, info);
-	if (err)
-		goto give_sigsegv;
 
-	/* Clear all the bits of the ucontext we don't use.  */
-	err |= __clear_user(&frame->uc, offsetof(struct ucontext, uc_mcontext));
+	/* Create the ucontext.  */
 	err |= __put_user(0, &frame->uc.uc_flags);
 	err |= __put_user(NULL, &frame->uc.uc_link);
 	err |= __save_altstack(&frame->uc.uc_stack, regs->sp);
-	err |= setup_sigcontext(&frame->uc.uc_mcontext, regs, set->sig[0]);
+	err |= setup_sigcontext(regs, &frame->uc.uc_mcontext);
 
 	err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
 
@@ -207,9 +194,12 @@ static int setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
 
 	/* trampoline - the desired return ip is the retcode itself */
 	return_ip = (unsigned long)&frame->retcode;
-	/* This is l.ori r11,r0,__NR_sigreturn, l.sys 1 */
-	err |= __put_user(0xa960, (short *)(frame->retcode + 0));
-	err |= __put_user(__NR_rt_sigreturn, (short *)(frame->retcode + 2));
+	/* This is:
+		l.ori r11,r0,__NR_sigreturn
+		l.sys 1
+	 */
+	err |= __put_user(0xa960,             (short *)(frame->retcode + 0));
+	err |= __put_user(__NR_rt_sigreturn,  (short *)(frame->retcode + 2));
 	err |= __put_user(0x20000001, (unsigned long *)(frame->retcode + 4));
 	err |= __put_user(0x15000000, (unsigned long *)(frame->retcode + 8));
 
@@ -262,82 +252,106 @@ handle_signal(unsigned long sig,
  * mode below.
  */
 
-void do_signal(struct pt_regs *regs)
+int do_signal(struct pt_regs *regs, int syscall)
 {
 	siginfo_t info;
 	int signr;
 	struct k_sigaction ka;
-
-	/*
-	 * We want the common case to go fast, which
-	 * is why we may in certain cases get here from
-	 * kernel mode. Just return without doing anything
-	 * if so.
-	 */
-	if (!user_mode(regs))
-		return;
-
-	signr = get_signal_to_deliver(&info, &ka, regs, NULL);
-
-	/* If we are coming out of a syscall then we need
-	 * to check if the syscall was interrupted and wants to be
-	 * restarted after handling the signal.  If so, the original
-	 * syscall number is put back into r11 and the PC rewound to
-	 * point at the l.sys instruction that resulted in the
-	 * original syscall.  Syscall results other than the four
-	 * below mean that the syscall executed to completion and no
-	 * restart is necessary.
-	 */
-	if (regs->orig_gpr11) {
-		int restart = 0;
-
-		switch (regs->gpr[11]) {
+	unsigned long continue_addr = 0;
+	unsigned long restart_addr = 0;
+	unsigned long retval = 0;
+	int restart = 0;
+
+	if (syscall) {
+		continue_addr = regs->pc;
+		restart_addr = continue_addr - 4;
+		retval = regs->gpr[11];
+
+		/*
+		 * Setup syscall restart here so that a debugger will
+		 * see the already changed PC.
+		 */
+		switch (retval) {
 		case -ERESTART_RESTARTBLOCK:
+			restart = -2;
+			/* Fall through */
 		case -ERESTARTNOHAND:
-			/* Restart if there is no signal handler */
-			restart = (signr <= 0);
-			break;
 		case -ERESTARTSYS:
-			/* Restart if there no signal handler or
-			 * SA_RESTART flag is set */
-			restart = (signr <= 0 || (ka.sa.sa_flags & SA_RESTART));
-			break;
 		case -ERESTARTNOINTR:
-			/* Always restart */
-			restart = 1;
+			restart++;
+			regs->gpr[11] = regs->orig_gpr11;
+			regs->pc = restart_addr;
 			break;
 		}
+	}
 
-		if (restart) {
-			if (regs->gpr[11] == -ERESTART_RESTARTBLOCK)
-				regs->gpr[11] = __NR_restart_syscall;
-			else
-				regs->gpr[11] = regs->orig_gpr11;
-			regs->pc -= 4;
-		} else {
-			regs->gpr[11] = -EINTR;
+	/*
+	 * Get the signal to deliver.  When running under ptrace, at this
+	 * point the debugger may change all our registers ...
+	 */
+	signr = get_signal_to_deliver(&info, &ka, regs, NULL);
+	/*
+	 * Depending on the signal settings we may need to revert the
+	 * decision to restart the system call.  But skip this if a
+	 * debugger has chosen to restart at a different PC.
+	 */
+	if (signr > 0) {
+		if (unlikely(restart) && regs->pc == restart_addr) {
+			if (retval == -ERESTARTNOHAND ||
+			    retval == -ERESTART_RESTARTBLOCK
+			    || (retval == -ERESTARTSYS
+			        && !(ka.sa.sa_flags & SA_RESTART))) {
+				/* No automatic restart */
+				regs->gpr[11] = -EINTR;
+				regs->pc = continue_addr;
+			}
 		}
-	}
 
-	if (signr <= 0) {
-		/* no signal to deliver so we just put the saved sigmask
-		 * back */
-		restore_saved_sigmask();
-	} else {		/* signr > 0 */
-		/* Whee!  Actually deliver the signal.  */
 		handle_signal(signr, &info, &ka, regs);
+	} else {
+		/* no handler */
+		restore_saved_sigmask();
+		/*
+		 * Restore pt_regs PC as syscall restart will be handled by
+		 * kernel without return to userspace
+		 */
+		if (unlikely(restart) && regs->pc == restart_addr) {
+			regs->pc = continue_addr;
+			return restart;
+		}
 	}
 
-	return;
+	return 0;
 }
 
-asmlinkage void do_notify_resume(struct pt_regs *regs)
+asmlinkage int
+do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
 {
-	if (current_thread_info()->flags & _TIF_SIGPENDING)
-		do_signal(regs);
-
-	if (current_thread_info()->flags & _TIF_NOTIFY_RESUME) {
-		clear_thread_flag(TIF_NOTIFY_RESUME);
-		tracehook_notify_resume(regs);
-	}
+	do {
+		if (likely(thread_flags & _TIF_NEED_RESCHED)) {
+			schedule();
+		} else {
+			if (unlikely(!user_mode(regs)))
+				return 0;
+			local_irq_enable();
+			if (thread_flags & _TIF_SIGPENDING) {
+				int restart = do_signal(regs, syscall);
+				if (unlikely(restart)) {
+					/*
+					 * Restart without handlers.
+					 * Deal with it without leaving
+					 * the kernel space.
+					 */
+					return restart;
+				}
+				syscall = 0;
+			} else {
+				clear_thread_flag(TIF_NOTIFY_RESUME);
+				tracehook_notify_resume(regs);
+			}
+		}
+		local_irq_disable();
+		thread_flags = current_thread_info()->flags;
+	} while (thread_flags & _TIF_WORK_MASK);
+	return 0;
 }