Linux native: Use TRAP_BRKPT/TRAP_HWBPT

This patch adjusts the native Linux target backend to tell the core
whether a trap was caused by a breakpoint.

It teaches the target to get that information out of the si_code of
the SIGTRAP siginfo.

Tested on x86-64 Fedora 20, s390 RHEL 7, and PPC64 Fedora 18.  An
earlier version was tested on ARM Fedora 21.

gdb/ChangeLog:
2015-03-04  Pedro Alves  <palves@redhat.com>

	* linux-nat.c (save_sigtrap): Check for breakpoints before
	checking watchpoints.
	(status_callback) [USE_SIGTRAP_SIGINFO]: Don't check whether a
	breakpoint is inserted if relying on SIGTRAP's siginfo.si_code.
	(check_stopped_by_breakpoint) [USE_SIGTRAP_SIGINFO]: Decide whether
	a breakpoint triggered based on the SIGTRAP's siginfo.si_code.
	(linux_nat_stopped_by_sw_breakpoint)
	(linux_nat_supports_stopped_by_sw_breakpoint)
	(linux_nat_stopped_by_hw_breakpoint)
	(linux_nat_supports_stopped_by_hw_breakpoint): New functions.
	(linux_nat_wait_1): Don't re-increment the PC if relying on
	SIGTRAP's siginfo->si_code.
	(linux_nat_add_target): Install new target methods.
	* linux-thread-db.c (check_event): Don't account for breakpoint PC
	offset if the target already adjusted the PC.
	* nat/linux-ptrace.h (USE_SIGTRAP_SIGINFO): New.
	(GDB_ARCH_TRAP_BRKPT): New.
	(TRAP_HWBKPT): Define if not already defined.

1 files changed, 104 insertions, 5 deletions

diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index 09edaf9..af77df2 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -2399,11 +2399,19 @@ save_sigtrap (struct lwp_info *lp)
   gdb_assert (lp->stop_reason == TARGET_STOPPED_BY_NO_REASON);
   gdb_assert (lp->status != 0);
 
-  if (check_stopped_by_watchpoint (lp))
-    return;
-
+  /* Check first if this was a SW/HW breakpoint before checking
+     watchpoints, because at least s390 can't tell the data address of
+     hardware watchpoint hits, and the kernel returns
+     stopped-by-watchpoint as long as there's a watchpoint set.  */
   if (linux_nat_status_is_event (lp->status))
     check_stopped_by_breakpoint (lp);
+
+  /* Note that TRAP_HWBKPT can indicate either a hardware breakpoint
+     or hardware watchpoint.  Check which is which if we got
+     TARGET_STOPPED_BY_HW_BREAKPOINT.  */
+  if (lp->stop_reason == TARGET_STOPPED_BY_NO_REASON
+      || lp->stop_reason == TARGET_STOPPED_BY_HW_BREAKPOINT)
+    check_stopped_by_watchpoint (lp);
 }
 
 /* Returns true if the LWP had stopped for a watchpoint.  */
@@ -2557,6 +2565,8 @@ status_callback (struct lwp_info *lp, void *data)
 				paddress (target_gdbarch (), pc));
 	  discard = 1;
 	}
+
+#if !USE_SIGTRAP_SIGINFO
       else if (!breakpoint_inserted_here_p (get_regcache_aspace (regcache), pc))
 	{
 	  if (debug_linux_nat)
@@ -2567,6 +2577,7 @@ status_callback (struct lwp_info *lp, void *data)
 
 	  discard = 1;
 	}
+#endif
 
       if (discard)
 	{
@@ -2669,10 +2680,49 @@ check_stopped_by_breakpoint (struct lwp_info *lp)
   struct gdbarch *gdbarch = get_regcache_arch (regcache);
   CORE_ADDR pc;
   CORE_ADDR sw_bp_pc;
+#if USE_SIGTRAP_SIGINFO
+  siginfo_t siginfo;
+#endif
 
   pc = regcache_read_pc (regcache);
   sw_bp_pc = pc - target_decr_pc_after_break (gdbarch);
 
+#if USE_SIGTRAP_SIGINFO
+  if (linux_nat_get_siginfo (lp->ptid, &siginfo))
+    {
+      if (siginfo.si_signo == SIGTRAP)
+	{
+	  if (siginfo.si_code == GDB_ARCH_TRAP_BRKPT)
+	    {
+	      if (debug_linux_nat)
+		fprintf_unfiltered (gdb_stdlog,
+				    "CSBB: Push back software "
+				    "breakpoint for %s\n",
+				    target_pid_to_str (lp->ptid));
+
+	      /* Back up the PC if necessary.  */
+	      if (pc != sw_bp_pc)
+		regcache_write_pc (regcache, sw_bp_pc);
+
+	      lp->stop_pc = sw_bp_pc;
+	      lp->stop_reason = TARGET_STOPPED_BY_SW_BREAKPOINT;
+	      return 1;
+	    }
+	  else if (siginfo.si_code == TRAP_HWBKPT)
+	    {
+	      if (debug_linux_nat)
+		fprintf_unfiltered (gdb_stdlog,
+				    "CSBB: Push back hardware "
+				    "breakpoint/watchpoint for %s\n",
+				    target_pid_to_str (lp->ptid));
+
+	      lp->stop_pc = pc;
+	      lp->stop_reason = TARGET_STOPPED_BY_HW_BREAKPOINT;
+	      return 1;
+	    }
+	}
+    }
+#else
   if ((!lp->step || lp->stop_pc == sw_bp_pc)
       && software_breakpoint_inserted_here_p (get_regcache_aspace (regcache),
 					      sw_bp_pc))
@@ -2704,10 +2754,53 @@ check_stopped_by_breakpoint (struct lwp_info *lp)
       lp->stop_reason = TARGET_STOPPED_BY_HW_BREAKPOINT;
       return 1;
     }
+#endif
 
   return 0;
 }
 
+
+/* Returns true if the LWP had stopped for a software breakpoint.  */
+
+static int
+linux_nat_stopped_by_sw_breakpoint (struct target_ops *ops)
+{
+  struct lwp_info *lp = find_lwp_pid (inferior_ptid);
+
+  gdb_assert (lp != NULL);
+
+  return lp->stop_reason == TARGET_STOPPED_BY_SW_BREAKPOINT;
+}
+
+/* Implement the supports_stopped_by_sw_breakpoint method.  */
+
+static int
+linux_nat_supports_stopped_by_sw_breakpoint (struct target_ops *ops)
+{
+  return USE_SIGTRAP_SIGINFO;
+}
+
+/* Returns true if the LWP had stopped for a hardware
+   breakpoint/watchpoint.  */
+
+static int
+linux_nat_stopped_by_hw_breakpoint (struct target_ops *ops)
+{
+  struct lwp_info *lp = find_lwp_pid (inferior_ptid);
+
+  gdb_assert (lp != NULL);
+
+  return lp->stop_reason == TARGET_STOPPED_BY_HW_BREAKPOINT;
+}
+
+/* Implement the supports_stopped_by_hw_breakpoint method.  */
+
+static int
+linux_nat_supports_stopped_by_hw_breakpoint (struct target_ops *ops)
+{
+  return USE_SIGTRAP_SIGINFO;
+}
+
 /* Select one LWP out of those that have events pending.  */
 
 static void
@@ -3360,8 +3453,10 @@ linux_nat_wait_1 (struct target_ops *ops,
   gdb_assert (lp != NULL);
 
   /* Now that we've selected our final event LWP, un-adjust its PC if
-     it was a software breakpoint.  */
-  if (lp->stop_reason == TARGET_STOPPED_BY_SW_BREAKPOINT)
+     it was a software breakpoint, and we can't reliably support the
+     "stopped by software breakpoint" stop reason.  */
+  if (lp->stop_reason == TARGET_STOPPED_BY_SW_BREAKPOINT
+      && !USE_SIGTRAP_SIGINFO)
     {
       struct regcache *regcache = get_thread_regcache (lp->ptid);
       struct gdbarch *gdbarch = get_regcache_arch (regcache);
@@ -4651,6 +4746,10 @@ linux_nat_add_target (struct target_ops *t)
   t->to_thread_address_space = linux_nat_thread_address_space;
   t->to_stopped_by_watchpoint = linux_nat_stopped_by_watchpoint;
   t->to_stopped_data_address = linux_nat_stopped_data_address;
+  t->to_stopped_by_sw_breakpoint = linux_nat_stopped_by_sw_breakpoint;
+  t->to_supports_stopped_by_sw_breakpoint = linux_nat_supports_stopped_by_sw_breakpoint;
+  t->to_stopped_by_hw_breakpoint = linux_nat_stopped_by_hw_breakpoint;
+  t->to_supports_stopped_by_hw_breakpoint = linux_nat_supports_stopped_by_hw_breakpoint;
 
   t->to_can_async_p = linux_nat_can_async_p;
   t->to_is_async_p = linux_nat_is_async_p;