Re: [PATCH] powerpc/ptrace: remove BUG_ON when full register set not available

On Wed, 2011-03-02 at 14:08 +1100, Benjamin Herrenschmidt wrote:

quoted

--- ptracev2.orig/include/linux/regset.h	2011-02-20 12:15:57.000000000 -0600
+++ ptracev2/include/linux/regset.h	2011-02-28 13:33:36.685302349 -0600

@@ -240,6 +240,34 @@ static inline int user_regset_copyout(un
 	}
 	return 0;
 }
+/* want the count to be the registers 14-31 inclusive */
+#define POISON_REG_CNT (PT_R31-PT_R14+1)
+static inline int user_regset_copyout_poison(unsigned int *pos,
+					   unsigned int *count,
+					   void **kbuf, void __user **ubuf,
+					   const int start_pos,
+					   const int end_pos)
+{

I wouldn't put that in a generic location... especially something
like POISON_REG_CNT is very specific to powerpc and our ABI.

Yeah I put it there thinking about readability but only use it in the
one place.  If we go forward with this current strategy I will remove
the #define and just comment more.

.../...

quoted

 static inline int user_regset_copyin(unsigned int *pos, unsigned int *count,
 				     const void **kbuf,

--- ptracev2.orig/arch/powerpc/kernel/ptrace.c	2011-02-20 12:15:57.000000000 -0600
+++ ptracev2/arch/powerpc/kernel/ptrace.c	2011-03-01 13:49:12.686354353 -0600

@@ -234,11 +234,29 @@ static int gpr_get(struct task_struct *t
 	if (target->thread.regs == NULL)
 		return -EIO;
 
-	CHECK_FULL_REGS(target->thread.regs);

Wouldn't it be a simpler/cleaner approach to use a single function call
here that checks if the reg set is full and if not, put poison values
in the thread.regs structure itself ?

The resulting code would be more palatable...

That was actually the way I had done the first patch while debugging the
problem but Paul Mackerras didn't like that I changed the thread struct.

It is not clear to me which is better.  Reporting a poison value that 
isn't actually there or to change the data.  Hopefully a consensus can
be reached and then I can submit a new patch based on that.

Cheers,
Ben.

quoted

-	ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf,
-				  target->thread.regs,
-				  0, offsetof(struct pt_regs, msr));
+	if (!FULL_REGS(target->thread.regs)) {
+                /* Don't have the full register set. Copy out register r0-r13 */
+		ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf,
+					  target->thread.regs,
+					  0, sizeof(long)*PT_R14);
+
+		/* Dont want to change the actual register values so rather than read the */
+		/* actual register copy a poison value into the buffer instead		  */
+		if (!ret)
+			ret = user_regset_copyout_poison(&pos, &count, &kbuf, &ubuf,
+						  sizeof(long)*PT_R14, offsetof(struct pt_regs, nip));
+
+		/* Copy out the rest of the registers as usual */
+		if (!ret)
+			ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf,
+						  target->thread.regs,
+						  offsetof(struct pt_regs, nip), offsetof(struct pt_regs, msr));
+		
+	} else 
+		ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf,
+					  target->thread.regs,
+					  0, offsetof(struct pt_regs, msr));
 	if (!ret) {
 		unsigned long msr = get_user_msr(target);
 		ret = user_regset_copyout(&pos, &count, &kbuf, &ubuf, &msr,

@@ -645,11 +663,29 @@ static int gpr32_get(struct task_struct 
 	if (target->thread.regs == NULL)
 		return -EIO;
 
-	CHECK_FULL_REGS(target->thread.regs);
-
 	pos /= sizeof(reg);
 	count /= sizeof(reg);
 
+	if(!FULL_REGS(target->thread.regs)) {
+		if (kbuf) {
+                	/* Don't have the full register set. Copy out register r0-r13 */
+			for (; count > 0 && pos < PT_R14; --count)
+				*k++ = regs[pos++];
+
+			/* Dont want to change the actual register values so rather than read the */
+			/* actual register copy a poison value into the buffer instead		  */
+			for (; count > 0 && pos <= PT_R31; --count,pos++)
+				*k++ = 0xdeadbeef;
+
+		} else { 
+			for (; count > 0 && pos < PT_R14; --count)
+				if (__put_user((compat_ulong_t) regs[pos++], u++))
+					return -EFAULT;
+			for (; count > 0 && pos <= PT_R31; --count,pos++)
+				if (__put_user((compat_ulong_t) 0xdeadbeef, u++))
+					return -EFAULT;
+		}
+	}
 	if (kbuf)
 		for (; count > 0 && pos < PT_MSR; --count)
 			*k++ = regs[pos++];

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