powerpc: trap_is_syscall() helper to hide syscall trap number

A new system call interrupt will be added with a new trap number.
Hide the explicit 0xc00 test behind an accessor to reduce churn
in callers.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Make it a static inline]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200507121332.2233629-3-mpe@ellerman.id.au

arch/powerpc/include/asm/ptrace.h

@@ -222,6 +222,11 @@ static inline void set_trap(struct pt_regs *regs, unsigned long val)
 	regs->trap = (regs->trap & TRAP_FLAGS_MASK) | (val & ~TRAP_FLAGS_MASK);
 }
 
+static inline bool trap_is_syscall(struct pt_regs *regs)
+{
+	return TRAP(regs) == 0xc00;
+}
+
 #define arch_has_single_step()	(1)
 #ifndef CONFIG_BOOK3S_601
 #define arch_has_block_step()	(true)

arch/powerpc/include/asm/syscall.h

@@ -26,7 +26,10 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 	 * This is important for seccomp so that compat tasks can set r0 = -1
 	 * to reject the syscall.
 	 */
-	return TRAP(regs) == 0xc00 ? regs->gpr[0] : -1;
+	if (trap_is_syscall(regs))
+		return regs->gpr[0];
+	else
+		return -1;
 }
 
 static inline void syscall_rollback(struct task_struct *task,

arch/powerpc/kernel/process.c

@@ -1413,7 +1413,7 @@ void show_regs(struct pt_regs * regs)
 	print_msr_bits(regs->msr);
 	pr_cont("  CR: %08lx  XER: %08lx\n", regs->ccr, regs->xer);
 	trap = TRAP(regs);
-	if ((TRAP(regs) != 0xc00) && cpu_has_feature(CPU_FTR_CFAR))
+	if (!trap_is_syscall(regs) && cpu_has_feature(CPU_FTR_CFAR))
 		pr_cont("CFAR: "REG" ", regs->orig_gpr3);
 	if (trap == 0x200 || trap == 0x300 || trap == 0x600)
 #if defined(CONFIG_4xx) || defined(CONFIG_BOOKE)

arch/powerpc/kernel/signal.c

@@ -198,7 +198,7 @@ static void check_syscall_restart(struct pt_regs *regs, struct k_sigaction *ka,
 	int restart = 1;
 
 	/* syscall ? */
-	if (TRAP(regs) != 0x0C00)
+	if (!trap_is_syscall(regs))
 		return;
 
 	/* error signalled ? */

arch/powerpc/xmon/xmon.c

@@ -1776,7 +1776,7 @@ static void prregs(struct pt_regs *fp)
 #endif
 	printf("pc  = ");
 	xmon_print_symbol(fp->nip, " ", "\n");
-	if (TRAP(fp) != 0xc00 && cpu_has_feature(CPU_FTR_CFAR)) {
+	if (!trap_is_syscall(fp) && cpu_has_feature(CPU_FTR_CFAR)) {
 		printf("cfar= ");
 		xmon_print_symbol(fp->orig_gpr3, " ", "\n");
 	}