[PATCH 2/4] powerpc: Use SET_TRAP and avoid open-coding trap masking

[Nicholas Piggin]

The pt_regs.trap field keeps 4 low bits for some metadata about the
trap or how it was handled, which is masked off in order to test the
architectural trap number.

Add a SET_TRAP() accessor to set this, equivalent to TRAP() for
returning it. This is actually not quite the equivalent of TRAP()
because it always clears the low bits, which may be harmless if
it can only be updated via ptrace syscall, but it seems dangerous.
In fact settting TRAP from ptrace doesn't seem like a great idea
so maybe it's better deleted.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 arch/powerpc/include/asm/ptrace.h        | 3 +++
 arch/powerpc/kernel/ptrace/ptrace-tm.c   | 2 +-
 arch/powerpc/kernel/ptrace/ptrace-view.c | 2 +-
 arch/powerpc/xmon/xmon.c                 | 2 +-
 4 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/ptrace.h b/arch/powerpc/include/asm/ptrace.h
index 89f31d5a8062..7eaa2ecfd0b7 100644
--- a/arch/powerpc/include/asm/ptrace.h
+++ b/arch/powerpc/include/asm/ptrace.h
@@ -183,10 +183,12 @@ extern int ptrace_put_reg(struct task_struct *task, int regno,
 #ifdef __powerpc64__
 #ifdef CONFIG_PPC_BOOK3S
 #define TRAP(regs)		((regs)->trap)
+#define SET_TRAP(regs, val)	((regs)->trap = (val))
 #define FULL_REGS(regs)		true
 #define SET_FULL_REGS(regs)	do { } while (0)
 #else
 #define TRAP(regs)		((regs)->trap & ~0x1)
+#define SET_TRAP(regs, val)	((regs)->trap = ((regs)->trap & 0x1) | ((val) & ~0x1))
 #define FULL_REGS(regs)		(((regs)->trap & 1) == 0)
 #define SET_FULL_REGS(regs)	((regs)->trap |= 1)
 #endif
@@ -201,6 +203,7 @@ extern int ptrace_put_reg(struct task_struct *task, int regno,
  * is a critical exception (1 means it is).
  */
 #define TRAP(regs)		((regs)->trap & ~0xF)
+#define SET_TRAP(regs, val)	((regs)->trap = ((regs)->trap & 0xF) | ((val) & ~0xF))
 #define FULL_REGS(regs)		(((regs)->trap & 1) == 0)
 #define SET_FULL_REGS(regs)	((regs)->trap |= 1)
 #define IS_CRITICAL_EXC(regs)	(((regs)->trap & 2) != 0)
diff --git a/arch/powerpc/kernel/ptrace/ptrace-tm.c b/arch/powerpc/kernel/ptrace/ptrace-tm.c
index d75aff31f637..ac76b2924a1a 100644
--- a/arch/powerpc/kernel/ptrace/ptrace-tm.c
+++ b/arch/powerpc/kernel/ptrace/ptrace-tm.c
@@ -43,7 +43,7 @@ static int set_user_ckpt_msr(struct task_struct *task, unsigned long msr)
 
 static int set_user_ckpt_trap(struct task_struct *task, unsigned long trap)
 {
-	task->thread.ckpt_regs.trap = trap & 0xfff0;
+	SET_TRAP(&task->thread.ckpt_regs, trap);
 	return 0;
 }
 
diff --git a/arch/powerpc/kernel/ptrace/ptrace-view.c b/arch/powerpc/kernel/ptrace/ptrace-view.c
index 15e3b79b6395..87c8bd67512c 100644
--- a/arch/powerpc/kernel/ptrace/ptrace-view.c
+++ b/arch/powerpc/kernel/ptrace/ptrace-view.c
@@ -149,7 +149,7 @@ static int set_user_dscr(struct task_struct *task, unsigned long dscr)
  */
 static int set_user_trap(struct task_struct *task, unsigned long trap)
 {
-	task->thread.regs->trap = trap & 0xfff0;
+	SET_TRAP(task->thread.regs, trap);
 	return 0;
 }
 
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 7af840c0fc93..20c1fc08819b 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -1178,7 +1178,7 @@ static int do_step(struct pt_regs *regs)
 				return 0;
 			}
 			if (stepped > 0) {
-				regs->trap = 0xd00 | (regs->trap & 1);
+				SET_TRAP(regs, 0xd00);
 				printf("stepped to ");
 				xmon_print_symbol(regs->nip, " ", "\n");
 				ppc_inst_dump(regs->nip, 1, 0);
-- 
2.23.0