[RFC/PATCH 5/5] powerpc: Allow ptrace write to pt_regs trap

[Benjamin Herrenschmidt]

This patch allows a ptracer to write to the "trap" word of the
pt_regs. This, along with the previous patch, should enable gdb
to properly handle syscall restarting after executing a separate
function (at least when there's no restart block).

Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>

 arch/powerpc/kernel/ptrace-common.h |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

Index: linux-cell/arch/powerpc/kernel/ptrace-common.h
===================================================================
--- linux-cell.orig/arch/powerpc/kernel/ptrace-common.h	2007-05-29 16:22:07.000000000 +1000
+++ linux-cell/arch/powerpc/kernel/ptrace-common.h	2007-05-29 16:42:04.000000000 +1000
@@ -41,10 +41,15 @@ static inline int put_reg(struct task_st
 	if (task->thread.regs == NULL)
 		return -EIO;
 
-	if (regno <= PT_MAX_PUT_REG) {
+	if (regno <= PT_MAX_PUT_REG || regno == PT_TRAP) {
 		if (regno == PT_MSR)
 			data = (data & MSR_DEBUGCHANGE)
 				| (task->thread.regs->msr & ~MSR_DEBUGCHANGE);
+		/* We prevent mucking around with the reserved area of trap
+		 * which are used internally by the kernel
+		 */
+		if (regno == PT_TRAP)
+			data &= 0xff00;
 		((unsigned long *)task->thread.regs)[regno] = data;
 		return 0;
 	}