[PATCH RFC 4/8] mips: implement syscall restart generically

[PATCH RFC 4/8] mips: implement syscall restart generically

[Jonas Bonn]

Manipulating task state to effect re-execution of an interrupted syscall
used to be purely architecture specific code.  However, as most arch's
were essentially just making minor adjustments to almost identical logic,
this code could be moved to a common implementation.

The generic variant introduces the function handle_syscall_restart() to be
called after get_signal_to_deliver().  The architecture specific register
manipulations required to effect the actual restart are now implemented
in the generic syscall interface found in asm/syscall.h

This patch transitions this architecture's signal handling code over to
using the generic syscall restart code by:

i)  Implementing the register manipulations in asm/syscall.h
ii) Replacing the restart logic with a call to handle_syscall_restart

Cc: linux-mips@linux-mips.org
Signed-off-by: Jonas Bonn <jonas@southpole.se>
---
 arch/mips/include/asm/syscall.h |   91 +++++++++++++++++++++++++++++++++++++++
 arch/mips/kernel/signal.c       |   40 +----------------
 2 files changed, 94 insertions(+), 37 deletions(-)
 create mode 100644 arch/mips/include/asm/syscall.h

diff --git a/arch/mips/include/asm/syscall.h b/arch/mips/include/asm/syscall.h
new file mode 100644
index 0000000..7280d95
--- /dev/null
+++ b/arch/mips/include/asm/syscall.h
@@ -0,0 +1,91 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * Copyright (C) 2011 Jonas Bonn <jonas@southpole.se>
+ */
+
+#ifndef _ASM_SYSCALL_H
+#define _ASM_SYSCALL_H
+
+#include <linux/err.h>
+#include <linux/sched.h>
+#include <asm/unistd.h>
+
+static inline int
+syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
+{
+	return regs->regs[0] ?: -1;
+}
+
+static inline void
+syscall_rollback(struct task_struct *task, struct pt_regs *regs)
+{
+	regs->regs[2] = regs->regs[0];
+	regs->regs[7] = regs->regs[26];
+}
+
+static inline void
+syscall_clear(struct task_struct *task, struct pt_regs *regs)
+{
+	regs->regs[0] = 0;
+}
+
+static inline void
+syscall_restart(struct task_struct *task, struct pt_regs *regs)
+{
+	syscall_rollback(task, regs);
+	regs->cp0_epc -= 4;
+}
+
+static inline void
+syscall_do_restartblock(struct task_struct *task, struct pt_regs *regs)
+{
+	regs->regs[2] = current->thread.abi->restart;
+	regs->regs[7] = regs->regs[26];
+	regs->cp0_epc -= 4;
+}
+
+static inline long
+syscall_get_error(struct task_struct *task, struct pt_regs *regs)
+{
+	/*
+	 * r7 == 1 if syscall returns error
+	 * r2 contains _positive_ result
+	 */
+	if (regs->regs[7])
+		return -regs->regs[2];
+	else
+		return 0;
+}
+
+static inline long
+syscall_get_return_value(struct task_struct *task, struct pt_regs *regs)
+{
+	return regs->gpr[2];
+}
+
+static inline void
+syscall_set_return_value(struct task_struct *task, struct pt_regs *regs,
+			 int error, long val)
+{
+	regs->gpr[2] = (long) error ? -error : val;
+}
+
+static inline void
+syscall_get_arguments(struct task_struct *task, struct pt_regs *regs,
+		      unsigned int i, unsigned int n, unsigned long *args)
+{
+	/* TODO */
+}
+
+static inline void
+syscall_set_arguments(struct task_struct *task, struct pt_regs *regs,
+		      unsigned int i, unsigned int n, const unsigned long *args)
+{
+	/* TODO */
+}
+
+#endif
diff --git a/arch/mips/kernel/signal.c b/arch/mips/kernel/signal.c
index dbbe0ce..13f2864 100644
--- a/arch/mips/kernel/signal.c
+++ b/arch/mips/kernel/signal.c
@@ -547,27 +547,6 @@ static int handle_signal(unsigned long sig, siginfo_t *info,
 	struct mips_abi *abi = current->thread.abi;
 	void *vdso = current->mm->context.vdso;
 
-	if (regs->regs[0]) {
-		switch(regs->regs[2]) {
-		case ERESTART_RESTARTBLOCK:
-		case ERESTARTNOHAND:
-			regs->regs[2] = EINTR;
-			break;
-		case ERESTARTSYS:
-			if (!(ka->sa.sa_flags & SA_RESTART)) {
-				regs->regs[2] = EINTR;
-				break;
-			}
-		/* fallthrough */
-		case ERESTARTNOINTR:
-			regs->regs[7] = regs->regs[26];
-			regs->regs[2] = regs->regs[0];
-			regs->cp0_epc -= 4;
-		}
-
-		regs->regs[0] = 0;		/* Don't deal with this again.  */
-	}
-
 	if (sig_uses_siginfo(ka))
 		ret = abi->setup_rt_frame(vdso + abi->rt_signal_return_offset,
 					  ka, regs, sig, oldset, info);
@@ -609,6 +588,9 @@ static void do_signal(struct pt_regs *regs)
 		oldset = &current->blocked;
 
 	signr = get_signal_to_deliver(&info, &ka, regs, NULL);
+
+	handle_syscall_restart(regs, &ka, (signr > 0));
+
 	if (signr > 0) {
 		/* Whee!  Actually deliver the signal.  */
 		if (handle_signal(signr, &info, &ka, oldset, regs) == 0) {
@@ -625,22 +607,6 @@ static void do_signal(struct pt_regs *regs)
 		return;
 	}
 
-	if (regs->regs[0]) {
-		if (regs->regs[2] == ERESTARTNOHAND ||
-		    regs->regs[2] == ERESTARTSYS ||
-		    regs->regs[2] == ERESTARTNOINTR) {
-			regs->regs[2] = regs->regs[0];
-			regs->regs[7] = regs->regs[26];
-			regs->cp0_epc -= 4;
-		}
-		if (regs->regs[2] == ERESTART_RESTARTBLOCK) {
-			regs->regs[2] = current->thread.abi->restart;
-			regs->regs[7] = regs->regs[26];
-			regs->cp0_epc -= 4;
-		}
-		regs->regs[0] = 0;	/* Don't deal with this again.  */
-	}
-
 	/*
 	 * If there's no signal to deliver, we just put the saved sigmask
 	 * back
-- 
1.7.5.4

Re: [PATCH RFC 4/8] mips: implement syscall restart generically

[Ralf Baechle]

On Sun, Oct 23, 2011 at 12:19:58PM +0200, Jonas Bonn wrote:

> Manipulating task state to effect re-execution of an interrupted syscall
> used to be purely architecture specific code.  However, as most arch's
> were essentially just making minor adjustments to almost identical logic,
> this code could be moved to a common implementation.
> 
> The generic variant introduces the function handle_syscall_restart() to be
> called after get_signal_to_deliver().  The architecture specific register
> manipulations required to effect the actual restart are now implemented
> in the generic syscall interface found in asm/syscall.h
> 
> This patch transitions this architecture's signal handling code over to
> using the generic syscall restart code by:
> 
> i)  Implementing the register manipulations in asm/syscall.h
> ii) Replacing the restart logic with a call to handle_syscall_restart

Nice cleanup.

Any reason why you add empty version of syscall_get_arguments and
syscall_set_version?  A non-functional version that causes a silent
failure is way worse than something that fails at compile time.

  Ralf

Re: [PATCH RFC 4/8] mips: implement syscall restart generically

[Jonas Bonn]

On 4 November 2011 10:32, Ralf Baechle <ralf@linux-mips.org> wrote:
>
> Nice cleanup.
>
> Any reason why you add empty version of syscall_get_arguments and
> syscall_set_version?  A non-functional version that causes a silent
> failure is way worse than something that fails at compile time.

Good point... I'll remove those empty functions for this patch series
and look into doing a proper implementation for them later.

Thanks for the review.

/Jonas