Subject: Re: [RFC/PATCH 4/4] powerpc: Make syscall restart code more common

From: Christoph Hellwig <[email-masked]>
Date: Sat, 2 Jun 2007 12:12:39 +0200

On Wed, May 30, 2007 at 06:05:16PM +1000, Benjamin Herrenschmidt wrote:
> This patch moves the code in signal_32.c and signal_64.c for handling
> syscall restart into a common signal-common.h file and converge around
> a single implementation that is based on the 32 bits one, using trap, ccr
> and r3 rather than the special "result" field for deciding what to do.
> 
> The "result" field is now pretty much deprecated. We still set it for
> the sake of whatever might rely on it in userland but we no longer use
> it's content.
> 
> This, along with a previous patch that enables ptracers to write to
> "trap" and "orig_r3" should allow gdb to properly handle syscall
> restarting.
> 
> There is only one common function for now and it's small enough so
> having it inline is fine. However, there is probably room for more
> merging of _32.c and _64.c in which case we'll probably want to
> have a common .c file and avoid inlines.

Here's an updated version to create a signal.[ch] instead.  It will be
used by the signal consolidation patches I'll post now.

Index: linux-2.6/arch/powerpc/kernel/signal_32.c
===================================================================
--- linux-2.6.orig/arch/powerpc/kernel/signal_32.c	2007-05-31 19:29:19.000000000 +0200
+++ linux-2.6/arch/powerpc/kernel/signal_32.c	2007-06-01 22:25:51.000000000 +0200
@@ -51,6 +51,8 @@
 #include <asm/pgtable.h>
 #endif
 
+#include "signal.h"
+
 #undef DEBUG_SIG
 
 #define _BLOCKABLE (~(sigmask(SIGKILL) | sigmask(SIGSTOP)))
@@ -1156,30 +1158,8 @@ int do_signal(sigset_t *oldset, struct p
 #ifdef CONFIG_PPC32
 no_signal:
 #endif
-	if (TRAP(regs) == 0x0C00		/* System Call! */
-	    && regs->ccr & 0x10000000		/* error signalled */
-	    && ((ret = regs->gpr[3]) == ERESTARTSYS
-		|| ret == ERESTARTNOHAND || ret == ERESTARTNOINTR
-		|| ret == ERESTART_RESTARTBLOCK)) {
-
-		if (signr > 0
-		    && (ret == ERESTARTNOHAND || ret == ERESTART_RESTARTBLOCK
-			|| (ret == ERESTARTSYS
-			    && !(ka.sa.sa_flags & SA_RESTART)))) {
-			/* make the system call return an EINTR error */
-			regs->result = -EINTR;
-			regs->gpr[3] = EINTR;
-			/* note that the cr0.SO bit is already set */
-		} else {
-			regs->nip -= 4;	/* Back up & retry system call */
-			regs->result = 0;
-			regs->trap = 0;
-			if (ret == ERESTART_RESTARTBLOCK)
-				regs->gpr[0] = __NR_restart_syscall;
-			else
-				regs->gpr[3] = regs->orig_gpr3;
-		}
-	}
+	/* Is there any syscall restart business here ? */
+	check_syscall_restart(regs, &ka, signr > 0);
 
 	if (signr == 0) {
 		/* No signal to deliver -- put the saved sigmask back */
Index: linux-2.6/arch/powerpc/kernel/signal_64.c
===================================================================
--- linux-2.6.orig/arch/powerpc/kernel/signal_64.c	2007-05-31 19:29:20.000000000 +0200
+++ linux-2.6/arch/powerpc/kernel/signal_64.c	2007-06-01 22:25:57.000000000 +0200
@@ -34,6 +34,8 @@
 #include <asm/syscalls.h>
 #include <asm/vdso.h>
 
+#include "signal.h"
+
 #define DEBUG_SIG 0
 
 #define _BLOCKABLE (~(sigmask(SIGKILL) | sigmask(SIGSTOP)))
@@ -463,41 +465,6 @@ static int handle_signal(unsigned long s
 	return ret;
 }
 
-static inline void syscall_restart(struct pt_regs *regs, struct k_sigaction *ka)
-{
-	switch ((int)regs->result) {
-	case -ERESTART_RESTARTBLOCK:
-	case -ERESTARTNOHAND:
-		/* ERESTARTNOHAND means that the syscall should only be
-		 * restarted if there was no handler for the signal, and since
-		 * we only get here if there is a handler, we dont restart.
-		 */
-		regs->result = -EINTR;
-		regs->gpr[3] = EINTR;
-		regs->ccr |= 0x10000000;
-		break;
-	case -ERESTARTSYS:
-		/* ERESTARTSYS means to restart the syscall if there is no
-		 * handler or the handler was registered with SA_RESTART
-		 */
-		if (!(ka->sa.sa_flags & SA_RESTART)) {
-			regs->result = -EINTR;
-			regs->gpr[3] = EINTR;
-			regs->ccr |= 0x10000000;
-			break;
-		}
-		/* fallthrough */
-	case -ERESTARTNOINTR:
-		/* ERESTARTNOINTR means that the syscall should be
-		 * called again after the signal handler returns.
-		 */
-		regs->gpr[3] = regs->orig_gpr3;
-		regs->nip -= 4;
-		regs->result = 0;
-		break;
-	}
-}
-
 /*
  * Note that 'init' is a special process: it doesn't get signals it doesn't
  * want to handle. Thus you cannot kill init even with a SIGKILL even by
@@ -522,13 +489,13 @@ int do_signal(sigset_t *oldset, struct p
 		oldset = &current->blocked;
 
 	signr = get_signal_to_deliver(&info, &ka, regs, NULL);
+
+	/* Is there any syscall restart business here ? */
+	check_syscall_restart(regs, &ka, signr > 0);
+
 	if (signr > 0) {
 		int ret;
 
-		/* Whee!  Actually deliver the signal.  */
-		if (TRAP(regs) == 0x0C00)
-			syscall_restart(regs, &ka);
-
 		/*
 		 * Reenable the DABR before delivering the signal to
 		 * user space. The DABR will have been cleared if it
@@ -537,6 +504,7 @@ int do_signal(sigset_t *oldset, struct p
 		if (current->thread.dabr)
 			set_dabr(current->thread.dabr);
 
+		/* Whee!  Actually deliver the signal.  */
 		ret = handle_signal(signr, &ka, &info, oldset, regs);
 
 		/* If a signal was successfully delivered, the saved sigmask is in
@@ -547,19 +515,6 @@ int do_signal(sigset_t *oldset, struct p
 		return ret;
 	}
 
-	if (TRAP(regs) == 0x0C00) {	/* System Call! */
-		if ((int)regs->result == -ERESTARTNOHAND ||
-		    (int)regs->result == -ERESTARTSYS ||
-		    (int)regs->result == -ERESTARTNOINTR) {
-			regs->gpr[3] = regs->orig_gpr3;
-			regs->nip -= 4; /* Back up & retry system call */
-			regs->result = 0;
-		} else if ((int)regs->result == -ERESTART_RESTARTBLOCK) {
-			regs->gpr[0] = __NR_restart_syscall;
-			regs->nip -= 4;
-			regs->result = 0;
-		}
-	}
 	/* No signal to deliver -- put the saved sigmask back */
 	if (test_thread_flag(TIF_RESTORE_SIGMASK)) {
 		clear_thread_flag(TIF_RESTORE_SIGMASK);
Index: linux-2.6/arch/powerpc/kernel/Makefile
===================================================================
--- linux-2.6.orig/arch/powerpc/kernel/Makefile	2007-06-01 22:26:00.000000000 +0200
+++ linux-2.6/arch/powerpc/kernel/Makefile	2007-06-01 22:26:11.000000000 +0200
@@ -12,7 +12,8 @@ endif
 
 obj-y				:= semaphore.o cputable.o ptrace.o syscalls.o \
 				   irq.o align.o signal_32.o pmc.o vdso.o \
-				   init_task.o process.o systbl.o idle.o
+				   init_task.o process.o systbl.o idle.o \
+				   signal.o
 obj-y				+= vdso32/
 obj-$(CONFIG_PPC64)		+= setup_64.o binfmt_elf32.o sys_ppc32.o \
 				   signal_64.o ptrace32.o \
Index: linux-2.6/arch/powerpc/kernel/signal.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6/arch/powerpc/kernel/signal.c	2007-06-01 22:28:16.000000000 +0200
@@ -0,0 +1,62 @@
+/*
+ *    Copyright (c) 2007 Benjamin Herrenschmidt, IBM Coproration
+ *    Extracted from signal_32.c and signal_64.c
+ *
+ * This file is subject to the terms and conditions of the GNU General
+ * Public License.  See the file README.legal in the main directory of
+ * this archive for more details.
+ */
+
+#include <linux/ptrace.h>
+#include <linux/signal.h>
+
+void check_syscall_restart(struct pt_regs *regs, struct k_sigaction *ka,
+		int has_handler)
+{
+	unsigned long ret = regs->gpr[3];
+	int restart = 1;
+
+	/* syscall ? */
+	if (TRAP(regs) != 0x0C00)
+		return;
+
+	/* error signalled ? */
+	if (!(regs->ccr & 0x10000000))
+		return;
+
+	switch (ret) {
+	case ERESTART_RESTARTBLOCK:
+	case ERESTARTNOHAND:
+		/* ERESTARTNOHAND means that the syscall should only be
+		 * restarted if there was no handler for the signal, and since
+		 * we only get here if there is a handler, we dont restart.
+		 */
+		restart = !has_handler;
+		break;
+	case ERESTARTSYS:
+		/* ERESTARTSYS means to restart the syscall if there is no
+		 * handler or the handler was registered with SA_RESTART
+		 */
+		restart = !has_handler || (ka->sa.sa_flags & SA_RESTART) != 0;
+		break;
+	case ERESTARTNOINTR:
+		/* ERESTARTNOINTR means that the syscall should be
+		 * called again after the signal handler returns.
+		 */
+		break;
+	default:
+		return;
+	}
+	if (restart) {
+		if (ret == ERESTART_RESTARTBLOCK)
+			regs->gpr[0] = __NR_restart_syscall;
+		else
+			regs->gpr[3] = regs->orig_gpr3;
+		regs->nip -= 4;
+		regs->result = 0;
+	} else {
+		regs->result = -EINTR;
+		regs->gpr[3] = EINTR;
+		regs->ccr |= 0x10000000;
+	}
+}
Index: linux-2.6/arch/powerpc/kernel/signal.h
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6/arch/powerpc/kernel/signal.h	2007-06-01 22:25:26.000000000 +0200
@@ -0,0 +1,3 @@
+
+void check_syscall_restart(struct pt_regs *regs, struct k_sigaction *ka,
+		int has_handler);