[ARM] Add restart block infrastructure

Add the necessary infrastructure to handle restartable syscalls via
the restart_block method.  This isn't perfect, since we are unable
to modify the syscall number with ARM executables (it's typically
encoded into the instruction in the text segment) so instead we
build some code on the user space stack.

There is a potential problem - what happens if we are sleeping,
someone suspends us, resume (we continue to sleep via the restart
block method) suspend and then resume again?  We will build two
sets of restart code on the user stack.  This is probably a little
inefficient, but it should be harmless.

arch/arm/kernel/calls.S

@@ -14,7 +14,7 @@
 #else
 
 __syscall_start:
-/* 0 */		.long	sys_ni_syscall
+/* 0 */		.long	sys_restart_syscall
 		.long	sys_exit
 		.long	sys_fork_wrapper
 		.long	sys_read

arch/arm/kernel/signal.c

@@ -603,7 +603,7 @@ static int do_signal(sigset_t *oldset, struct pt_regs *regs, int syscall)
 			case SIGQUIT: case SIGILL: case SIGTRAP:
 			case SIGABRT: case SIGFPE: case SIGSEGV:
 			case SIGBUS: case SIGSYS: case SIGXCPU: case SIGXFSZ:
-				if (do_coredump(signr, regs))
+				if (do_coredump(signr, exit_code, regs))
 					exit_code |= 0x80;
 				/* FALLTHRU */
 
@@ -615,7 +615,11 @@ static int do_signal(sigset_t *oldset, struct pt_regs *regs, int syscall)
 
 		/* Are we from a system call? */
 		if (syscall) {
+			/* If so, check system call restarting.. */
 			switch (regs->ARM_r0) {
+			case -ERESTART_RESTARTBLOCK:
+				current_thread_info()->restart_block.fn =
+					do_no_restart_syscall;
 			case -ERESTARTNOHAND:
 				regs->ARM_r0 = -EINTR;
 				break;
@@ -638,13 +642,36 @@ static int do_signal(sigset_t *oldset, struct pt_regs *regs, int syscall)
 		return 1;
 	}
 
-	if (syscall &&
-	    (regs->ARM_r0 == -ERESTARTNOHAND ||
+	/*
+	 * No signal to deliver to the process - restart the syscall.
+	 */
+	if (syscall) {
+		if (regs->ARM_r0 == -ERESTART_RESTARTBLOCK) {
+			if (thumb_mode(regs)) {
+				regs->ARM_r7 = __NR_restart_syscall;
+				regs->ARM_pc -= 2;
+			} else {
+				u32 *usp;
+
+				regs->ARM_sp -= 12;
+				usp = (u32 *)regs->ARM_sp;
+
+				put_user(regs->ARM_pc, &usp[0]);
+				/* swi __NR_restart_syscall */
+				put_user(0xef000000 | __NR_restart_syscall, &usp[1]);
+				/* ldr	pc, [sp], #12 */
+				put_user(0xe49df00c, &usp[2]);
+
+				regs->ARM_pc = regs->ARM_sp + 4;
+			}
+		}
+		if (regs->ARM_r0 == -ERESTARTNOHAND ||
 		    regs->ARM_r0 == -ERESTARTSYS ||
-	     regs->ARM_r0 == -ERESTARTNOINTR)) {
+		    regs->ARM_r0 == -ERESTARTNOINTR) {
 			regs->ARM_r0 = regs->ARM_ORIG_r0;
 			regs->ARM_pc -= 4;
 		}
+	}
 	if (single_stepping)
 		ptrace_set_bpt(current);
 	return 0;

include/asm-arm/current.h

 #ifndef _ASMARM_CURRENT_H
 #define _ASMARM_CURRENT_H
 
-#include <asm/thread_info.h>
+#include <linux/thread_info.h>
 
 static inline struct task_struct *get_current(void) __attribute__ (( __const__ ));
 

include/asm-arm/thread_info.h

@@ -51,16 +51,20 @@ struct thread_info {
 	__u32			cpu;		/* cpu */
 	__u32			cpu_domain;	/* cpu domain */
 	struct cpu_context_save	cpu_context;	/* cpu context */
+	struct restart_block    restart_block;
 	union fp_state		fpstate;
 };
 
 #define INIT_THREAD_INFO(tsk)				\
 {							\
-	task:		&tsk,			\
-	exec_domain:	&default_exec_domain,	\
-	flags:		0,			\
-	preempt_count:	0,			\
-	addr_limit:	KERNEL_DS,		\
+	.task		= &tsk,				\
+	.exec_domain	= &default_exec_domain,		\
+	.flags		= 0,				\
+	.preempt_count	= 1,				\
+	.addr_limit	= KERNEL_DS,			\
+	.restart_block	= {				\
+		.fn	= do_no_restart_syscall,	\
+	},						\
 	INIT_EXTRA_THREAD_INFO,				\
 }
 

include/asm-arm/unistd.h

@@ -25,6 +25,7 @@
  * This file contains the system call numbers.
  */
 
+#define __NR_restart_syscall		(__NR_SYSCALL_BASE+  0)
 #define __NR_exit			(__NR_SYSCALL_BASE+  1)
 #define __NR_fork			(__NR_SYSCALL_BASE+  2)
 #define __NR_read			(__NR_SYSCALL_BASE+  3)