[PATCH] Fix for OProfile callgraph for Power 64 bit user apps

[Carl Love]

The following patch fixes the 64 bit user code backtrace 
which currently may hang the system.  

Signed-off-by: Carl Love <carll at us.ibm.com>

Index: linux-2.6.25.1/arch/powerpc/oprofile/backtrace.c
===================================================================
--- linux-2.6.25.1.orig/arch/powerpc/oprofile/backtrace.c	2008-05-01 16:45:25.000000000 -0500
+++ linux-2.6.25.1/arch/powerpc/oprofile/backtrace.c	2008-05-07 11:29:02.000000000 -0500
@@ -53,19 +53,40 @@
 #ifdef CONFIG_PPC64
 static unsigned long user_getsp64(unsigned long sp, int is_first)
 {
-	unsigned long stack_frame[3];
+	unsigned long stk_frm_lr;
+	unsigned long stk_frm_sp;
+	unsigned long size;
+
+	/* Issue the __copy_from_user_inatomic() third argument currently
+	 * only takes sizes 1, 2, 4 or 8 bytes.  Don't read more then the 
+	 * first 48 bytes of the stack frame.  That is all that is 
+	 * guaranteed to exist.  Reading more may cause the system to hang.
+	 *
+	 * 64 bit stack frame layout:
+	 * 0-7   bytes is the pointer to previous stack 
+	 * 8-15  bytes condition register save area
+	 * 16-23 bytes link register save area
+	 */
+	size = sizeof(unsigned long);
+	if (!access_ok(VERIFY_READ, (void __user *)sp, size))
+		return 0;
 
-	if (!access_ok(VERIFY_READ, (void __user *)sp, sizeof(stack_frame)))
+	if (__copy_from_user_inatomic(&stk_frm_sp, (void __user *)sp,
+					size))
 		return 0;
 
-	if (__copy_from_user_inatomic(stack_frame, (void __user *)sp,
-					sizeof(stack_frame)))
+	/* get the LR from the user stack */
+	if (!access_ok(VERIFY_READ, (void __user *)(sp+16), size))
+		return 0;
+
+	if (__copy_from_user_inatomic(&stk_frm_lr, (void __user *)(sp+16),
+					size))
 		return 0;
 
 	if (!is_first)
-		oprofile_add_trace(STACK_LR64(stack_frame));
+		oprofile_add_trace(stk_frm_lr);
 
-	return STACK_SP(stack_frame);
+	return stk_frm_sp;
 }
 #endif