ARC: gdbserver breakage in Big-Endian configuration #1

[Based on mainline commit 502a0c775c7f0a: "ARC: pt_regs update #5"]

gdbserver needs @stop_pc, served by ptrace, but fetched from pt_regs
differently, based on in_brkpt_traps(), which in turn relies on
additional machine state in pt_regs->event bitfield.

        unsigned long orig_r8:16, event:16;

For big endian config, this macro was returning false, despite being in
breakpoint Trap exception, causing wrong @stop_pc to be returned to gdb.

Issue #1: In BE, @event above is at offset 2 in word, while a STW insn
          at offset 0 was used to update it. Resort to using ST insn
	  which updates the half-word at right location.

Issue #2: The union involving bitfields causes all the members to be
	  laid out at offset 0. So with fix #1 above, ASM was now
	  updating at offset 2, "C" code was still referencing at
	  offset 0. Fixed by wrapping bitfield in a struct.

Reported-by: Noam Camus <noamc@ezchip.com>
Tested-by: Anton Kolesov <akolesov@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 4 insertions, 2 deletions

diff --git a/arch/arc/include/asm/ptrace.h b/arch/arc/include/asm/ptrace.h
index 6179de7e07c2..2046a89a57cf 100644
--- a/arch/arc/include/asm/ptrace.h
+++ b/arch/arc/include/asm/ptrace.h
@@ -52,12 +52,14 @@ struct pt_regs {
 
         /*to distinguish bet excp, syscall, irq */
         union {
+                struct {
 #ifdef CONFIG_CPU_BIG_ENDIAN
                 /* so that assembly code is same for LE/BE */
                 unsigned long orig_r8:16, event:16;
 #else
                 unsigned long event:16, orig_r8:16;
 #endif
+                };
                 long orig_r8_word;
         };
 };
diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S
index 0c6d664d4a83..6dbe359c760d 100644
--- a/arch/arc/kernel/entry.S
+++ b/arch/arc/kernel/entry.S
@@ -498,7 +498,7 @@ tracesys_exit:
 trap_with_param:
 
         ; stop_pc info by gdb needs this info
-        stw orig_r8_IS_BRKPT, [sp, PT_orig_r8]
+        st  orig_r8_IS_BRKPT, [sp, PT_orig_r8]
 
         mov r0, r12
         lr  r1, [efa]
@@ -723,7 +723,7 @@ not_exception:
         ; things to what they were, before returning from L2 context
         ;----------------------------------------------------------------
 
-        ldw  r9, [sp, PT_orig_r8]      ; get orig_r8 to make sure it is
+        ld   r9, [sp, PT_orig_r8]      ; get orig_r8 to make sure it is
         brne r9, orig_r8_IS_IRQ2, 149f ; infact a L2 ISR ret path
 
         ld r9, [sp, PT_status32]       ; get statu32_l2 (saved in pt_regs)