[PATCH] MIPS: ptrace: Fix PTRACE_PEEKUSR requests for 64-bit FGRs

[Maciej W. Rozycki]

Use 64-bit accesses for 64-bit floating-point general registers with 
PTRACE_PEEKUSR, removing the truncation of their upper halves in the 
FR=1 mode, caused by commit bbd426f542cb ("MIPS: Simplify FP context 
access"), which inadvertently switched them to using 32-bit accesses.

The PTRACE_POKEUSR side is fine as it's never been broken and continues 
using 64-bit accesses.

Cc: <stable@xxxxxxxxxxxxxxx> # 3.19+
Fixes: bbd426f542cb ("MIPS: Simplify FP context access")
Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxx>
---
Hi,

 Here's another one, spotted in the course of GDB PR gdb/22286 regression 
testing with the n64 ABI.  Please apply.

  Maciej
---
 arch/mips/kernel/ptrace.c   |    2 +-
 arch/mips/kernel/ptrace32.c |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

linux-mips-ptrace-peekusr-fp64.diff
Index: linux/arch/mips/kernel/ptrace.c
===================================================================
--- linux.orig/arch/mips/kernel/ptrace.c	2018-05-15 17:44:25.000000000 +0100
+++ linux/arch/mips/kernel/ptrace.c	2018-05-16 11:22:00.714605000 +0100
@@ -1070,7 +1070,7 @@ long arch_ptrace(struct task_struct *chi
 				break;
 			}
 #endif
-			tmp = get_fpr32(&fregs[addr - FPR_BASE], 0);
+			tmp = get_fpr64(&fregs[addr - FPR_BASE], 0);
 			break;
 		case PC:
 			tmp = regs->cp0_epc;
Index: linux/arch/mips/kernel/ptrace32.c
===================================================================
--- linux.orig/arch/mips/kernel/ptrace32.c	2018-05-15 17:45:16.000000000 +0100
+++ linux/arch/mips/kernel/ptrace32.c	2018-05-16 11:22:16.313698000 +0100
@@ -109,7 +109,7 @@ long compat_arch_ptrace(struct task_stru
 						addr & 1);
 				break;
 			}
-			tmp = get_fpr32(&fregs[addr - FPR_BASE], 0);
+			tmp = get_fpr64(&fregs[addr - FPR_BASE], 0);
 			break;
 		case PC:
 			tmp = regs->cp0_epc;