Subject: [PATCH] Fix ptrace compat wrapper for fpu register access

From: Andreas Schwab <[email-masked]>
Date: Sun, 29 Mar 2009 19:56:19 +0200

The ptrace compat wrapper mishandles access to the fpu registers.  The
PTRACE_PEEKUSR and PTRACE_POKEUSR requests miscalculate the index into
the fpr array due to the broken FPINDEX macro.  The
PPC_PTRACE_PEEKUSR_3264 request needs to use the same formula that the
native ptrace interface uses when operating on the register number (as
opposed to the 4-byte offset).  The PPC_PTRACE_POKEUSR_3264 request
didn't take TS_FPRWIDTH into account.

This was tested with the gdb testsuite on a G5.

Signed-off-by: Andreas Schwab <[email-masked]>

---
diff --git a/arch/powerpc/kernel/ptrace32.c b/arch/powerpc/kernel/ptrace32.c
index 197d49c..f992eaf 100644
--- a/arch/powerpc/kernel/ptrace32.c
+++ b/arch/powerpc/kernel/ptrace32.c
@@ -67,7 +67,7 @@ static long compat_ptrace_old(struct task_struct *child, long request,
 /* Macros to workout the correct index for the FPR in the thread struct */
 #define FPRNUMBER(i) (((i) - PT_FPR0) >> 1)
 #define FPRHALF(i) (((i) - PT_FPR0) & 1)
-#define FPRINDEX(i) TS_FPRWIDTH * FPRNUMBER(i) + FPRHALF(i)
+#define FPRINDEX(i) TS_FPRWIDTH * FPRNUMBER(i) * 2 + FPRHALF(i)
 
 long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
 			compat_ulong_t caddr, compat_ulong_t cdata)
@@ -169,7 +169,7 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
 		if (numReg >= PT_FPR0) {
 			flush_fp_to_thread(child);
 			tmp = ((unsigned long int *)child->thread.fpr)
-				[FPRINDEX(numReg)];
+				[TS_FPRWIDTH * (numReg - PT_FPR0)];
 		} else { /* register within PT_REGS struct */
 			tmp = ptrace_get_reg(child, numReg);
 		} 
@@ -263,7 +263,8 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
 			ret = ptrace_put_reg(child, numReg, freg);
 		} else {
 			flush_fp_to_thread(child);
-			((unsigned int *)child->thread.regs)[index] = data;
+			((unsigned int *)child->thread.regs)
+				[FPRINDEX(index)] = data;
 			ret = 0;
 		}
 		break;

-- 
Andreas Schwab, [email-masked]
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."