arm: new way of handling ERESTART_RESTARTBLOCK

new "syscall start" flag; handled in syscall_trace() by switching
syscall number to that of syscall_restart(2).  Restarts of that
kind (ERESTART_RESTARTBLOCK) are handled by setting that bit;
syscall number is not modified until the actual call.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index 9650c14..d407ebf 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -24,6 +24,7 @@
 #include <linux/hw_breakpoint.h>
 #include <linux/regset.h>
 #include <linux/audit.h>
+#include <linux/unistd.h>
 
 #include <asm/pgtable.h>
 #include <asm/traps.h>
@@ -916,6 +917,8 @@
 		audit_syscall_entry(AUDIT_ARCH_ARM, scno, regs->ARM_r0,
 				    regs->ARM_r1, regs->ARM_r2, regs->ARM_r3);
 
+	if (why == 0 && test_and_clear_thread_flag(TIF_SYSCALL_RESTARTSYS))
+		scno = __NR_restart_syscall - __NR_SYSCALL_BASE;
 	if (!test_thread_flag(TIF_SYSCALL_TRACE))
 		return scno;
 	if (!(current->ptrace & PT_PTRACED))