Handle MIPS Linux SIGTRAP siginfo.si_code values

This unbreaks pending/delayed breakpoints handling, as well as
hardware watchpoints, on MIPS.

Ref: https://sourceware.org/ml/gdb-patches/2016-02/msg00681.html

The MIPS kernel reports SI_KERNEL for all kernel generated traps,
instead of TRAP_BRKPT / TRAP_HWBKPT, but GDB isn't aware of this.

Basically, this commit:

- Folds watchpoints logic into check_stopped_by_breakpoint, and
  renames it to save_stop_reason.

- Adds GDB_ARCH_IS_TRAP_HWBKPT.

- Makes MIPS set both GDB_ARCH_IS_TRAP_BRPT and
  GDB_ARCH_IS_TRAP_HWBKPT to SI_KERNEL.  In save_stop_reason, we
  handle the case of the same si_code returning true for both
  TRAP_BRPT and TRAP_HWBKPT by looking at what the debug registers
  say.

Tested on x86-64 Fedora 20, native and gdbserver.

gdb/ChangeLog:
2016-02-24  Pedro Alves  <palves@redhat.com>

	* linux-nat.c (save_sigtrap) Delete.
	(stop_wait_callback): Call save_stop_reason instead of
	save_sigtrap.
	(check_stopped_by_breakpoint): Rename to ...
	(save_stop_reason): ... this.  Bits of save_sigtrap folded here.
	Use GDB_ARCH_IS_TRAP_HWBKPT and handle ambiguous
	GDB_ARCH_IS_TRAP_BRKPT / GDB_ARCH_IS_TRAP_HWBKPT.  Factor out
	common code between the USE_SIGTRAP_SIGINFO and
	!USE_SIGTRAP_SIGINFO blocks.
	(linux_nat_filter_event): Call save_stop_reason instead of
	save_sigtrap.
	* nat/linux-ptrace.h: Check for both SI_KERNEL and TRAP_BRKPT
	si_code for MIPS.
	* nat/linux-ptrace.h: Fix "TRAP_HWBPT" typo in x86 table.  Add
	comments on MIPS behavior.
	(GDB_ARCH_IS_TRAP_HWBKPT): Define for all archs.

gdb/gdbserver/ChangeLog:
2016-02-24  Pedro Alves  <palves@redhat.com>

	* linux-low.c (check_stopped_by_breakpoint): Rename to ...
	(save_stop_reason): ... this.  Use GDB_ARCH_IS_TRAP_HWBKPT and
	handle ambiguous GDB_ARCH_IS_TRAP_BRKPT / GDB_ARCH_IS_TRAP_HWBKPT.
	Factor out common code between the USE_SIGTRAP_SIGINFO and
	!USE_SIGTRAP_SIGINFO blocks.
	(linux_low_filter_event): Call save_stop_reason instead of
	check_stopped_by_breakpoint and check_stopped_by_watchpoint.
	Update comments.
	(linux_wait_1): Update comments.

1 files changed, 19 insertions, 0 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 95cabdb74f4..0d6ea60bf72 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,22 @@
+2016-02-24  Pedro Alves  <palves@redhat.com>
+
+	* linux-nat.c (save_sigtrap) Delete.
+	(stop_wait_callback): Call save_stop_reason instead of
+	save_sigtrap.
+	(check_stopped_by_breakpoint): Rename to ...
+	(save_stop_reason): ... this.  Bits of save_sigtrap folded here.
+	Use GDB_ARCH_IS_TRAP_HWBKPT and handle ambiguous
+	GDB_ARCH_IS_TRAP_BRKPT / GDB_ARCH_IS_TRAP_HWBKPT.  Factor out
+	common code between the USE_SIGTRAP_SIGINFO and
+	!USE_SIGTRAP_SIGINFO blocks.
+	(linux_nat_filter_event): Call save_stop_reason instead of
+	save_sigtrap.
+	* nat/linux-ptrace.h: Check for both SI_KERNEL and TRAP_BRKPT
+	si_code for MIPS.
+	* nat/linux-ptrace.h: Fix "TRAP_HWBPT" typo in x86 table.  Add
+	comments on MIPS behavior.
+	(GDB_ARCH_IS_TRAP_HWBKPT): Define for all archs.
+
 2016-02-24  Marcin Kościelnicki  <koriakin@0x04.net>
 
 	* rs6000-tdep.c (rs6000_frame_cache): Initialize frame and pc to 0