commit 17c28958600928109049a3bcc814b0d5bfb1ff3a
author Dave Martin <Dave.Martin@arm.com> Tue Aug 01 15:35:54 2017 +0100
committer Catalin Marinas <catalin.marinas@arm.com> Mon Aug 07 09:58:33 2017 +0100
tree 901508d772cc2fe2b33013b01b59ca990bd8f6c5
parent 35d0e6fb4d219d64ab3b7cffef7a11a0662140f5

arm64: Abstract syscallno manipulation

The -1 "no syscall" value is written in various ways, shared with
the user ABI in some places, and generally obscure.

This patch attempts to make things a little more consistent and
readable by replacing all these uses with a single #define.  A
couple of symbolic helpers are provided to clarify the intent
further.

Because the in-syscall check in do_signal() is changed from >= 0 to
!= NO_SYSCALL by this patch, different behaviour may be observable
if syscallno is set to values less than -1 by a tracer.  However,
this is not different from the behaviour that is already observable
if a tracer sets syscallno to a value >= __NR_(compat_)syscalls.

It appears that this can cause spurious syscall restarting, but
that is not a new behaviour either, and does not appear harmful.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/signal.c

diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 4d04b89..4991e87 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -36,6 +36,7 @@
 #include <asm/ucontext.h>
 #include <asm/unistd.h>
 #include <asm/fpsimd.h>
+#include <asm/ptrace.h>
 #include <asm/signal32.h>
 #include <asm/vdso.h>
 
@@ -387,7 +388,7 @@ static int restore_sigframe(struct pt_regs *regs,
 	/*
 	 * Avoid sys_rt_sigreturn() restarting.
 	 */
-	regs->syscallno = ~0;
+	forget_syscall(regs);
 
 	err |= !valid_user_regs(&regs->user_regs, current);
 	if (err == 0)
@@ -673,13 +674,12 @@ static void do_signal(struct pt_regs *regs)
 {
 	unsigned long continue_addr = 0, restart_addr = 0;
 	int retval = 0;
-	int syscall = regs->syscallno;
 	struct ksignal ksig;
 
 	/*
 	 * If we were from a system call, check for system call restarting...
 	 */
-	if (syscall >= 0) {
+	if (in_syscall(regs)) {
 		continue_addr = regs->pc;
 		restart_addr = continue_addr - (compat_thumb_mode(regs) ? 2 : 4);
 		retval = regs->regs[0];
@@ -687,7 +687,7 @@ static void do_signal(struct pt_regs *regs)
 		/*
 		 * Avoid additional syscall restarting via ret_to_user.
 		 */
-		regs->syscallno = ~0;
+		forget_syscall(regs);
 
 		/*
 		 * Prepare for system call restart. We do this here so that a
@@ -731,7 +731,7 @@ static void do_signal(struct pt_regs *regs)
 	 * Handle restarting a different system call. As above, if a debugger
 	 * has chosen to restart at a different PC, ignore the restart.
 	 */
-	if (syscall >= 0 && regs->pc == restart_addr) {
+	if (in_syscall(regs) && regs->pc == restart_addr) {
 		if (retval == -ERESTART_RESTARTBLOCK)
 			setup_restart_syscall(regs);
 		user_rewind_single_step(current);