http://sourceware.org/ml/gdb-patches/2015-02/msg00734.html

Subject: [PATCH 7/8] gdbserver/Linux: Use TRAP_BRKPT/TRAP_HWBPT

This patch adjusts gdbserver's Linux backend to tell gdbserver core

(and ultimately GDB) whether a trap was caused by a breakpoint.

It teaches the backend to get that information out of the si_code of

the SIGTRAP siginfo.

gdb/gdbserver/ChangeLog:

2015-02-25  Pedro Alves  <palves@redhat.com>

        * linux-low.c (check_stopped_by_breakpoint) [USE_SIGTRAP_SIGINFO]:

	Decide whether a breakpoint triggered based on the SIGTRAP's

	siginfo.si_code.

        (thread_still_has_status_pending_p) [USE_SIGTRAP_SIGINFO]: Don't check whether a

        breakpoint is inserted if relying on SIGTRAP's siginfo.si_code.

	(linux_low_filter_event): Check for breakpoints before checking

	watchpoints.

	(linux_wait_1): Don't re-increment the PC if relying on SIGTRAP's

	siginfo.si_code.

        (linux_stopped_by_sw_breakpoint)

        (linux_supports_stopped_by_sw_breakpoint)

        (linux_stopped_by_hw_breakpoint)

        (linux_supports_stopped_by_hw_breakpoint): New functions.

        (linux_target_ops): Install new target methods.

---

 gdb/gdbserver/linux-low.c | 122 +++++++++++++++++++++++++++++++++++++++++++---

 1 file changed, 116 insertions(+), 6 deletions(-)

Index: gdb-7.6.1/gdb/gdbserver/linux-low.c

===================================================================

--- gdb-7.6.1.orig/gdb/gdbserver/linux-low.c	2016-03-13 21:42:34.115589901 +0100

+++ gdb-7.6.1/gdb/gdbserver/linux-low.c	2016-03-13 21:45:00.625644976 +0100

@@ -1360,6 +1360,8 @@

   return (struct lwp_info*) find_inferior (&all_lwps, same_lwp, &ptid);

 }

+static void save_stop_reason (struct lwp_info *lwp);

+

 static struct lwp_info *

 linux_wait_for_lwp (ptid_t ptid, int *wstatp, int options)

 {

@@ -1465,6 +1467,10 @@

 	  current_inferior = saved_inferior;

 	}

+

+      /* RHEL */

+      if (!child->stopped_by_watchpoint)

+	save_stop_reason (child);

     }

   /* Store the STOP_PC, with adjustment applied.  This depends on the

@@ -1847,6 +1853,47 @@

    being stepped.  */

 ptid_t step_over_bkpt;

+// gdb/nat/linux-ptrace.h

+#if defined __i386__ || defined __x86_64__

+# define GDB_ARCH_IS_TRAP_BRKPT(X) ((X) == SI_KERNEL)

+# define GDB_ARCH_IS_TRAP_HWBKPT(X) ((X) == TRAP_HWBKPT)

+#elif defined __powerpc__

+# define GDB_ARCH_IS_TRAP_BRKPT(X) ((X) == SI_KERNEL || (X) == TRAP_BRKPT)

+# define GDB_ARCH_IS_TRAP_HWBKPT(X) ((X) == TRAP_HWBKPT)

+#elif defined __mips__

+# define GDB_ARCH_IS_TRAP_BRKPT(X) ((X) == SI_KERNEL)

+# define GDB_ARCH_IS_TRAP_HWBKPT(X) ((X) == SI_KERNEL)

+#else

+# define GDB_ARCH_IS_TRAP_BRKPT(X) ((X) == TRAP_BRKPT)

+# define GDB_ARCH_IS_TRAP_HWBKPT(X) ((X) == TRAP_HWBKPT)

+#endif

+

+// gdb/nat/linux-ptrace.h

+#ifndef TRAP_HWBKPT

+# define TRAP_HWBKPT 4

+#endif

+

+static void

+save_stop_reason (struct lwp_info *lwp)

+{

+  siginfo_t siginfo;

+

+  if (ptrace (PTRACE_GETSIGINFO, lwpid_of (lwp),

+              (PTRACE_ARG3_TYPE) 0, &siginfo) == 0)

+    {

+      if (siginfo.si_signo == SIGTRAP)

+        {

+          if (GDB_ARCH_IS_TRAP_HWBKPT (siginfo.si_code))

+	    {

+              /* This can indicate either a hardware breakpoint or

+                 hardware watchpoint.  Check debug registers.  */

+//              if (!check_stopped_by_watchpoint (lwp))

+		lwp->stopped_by_hw_breakpoint = 1;

+	    }

+	}

+    }

+}

+

 /* Wait for an event from child PID.  If PID is -1, wait for any

    child.  Store the stop status through the status pointer WSTAT.

    OPTIONS is passed to the waitpid call.  Return 0 if no child stop

@@ -3332,6 +3396,7 @@

   errno = 0;

   lwp->stopped = 0;

   lwp->stopped_by_watchpoint = 0;

+  lwp->stopped_by_hw_breakpoint = 0;

   lwp->stepping = step;

   ptrace (step ? PTRACE_SINGLESTEP : PTRACE_CONT, lwpid_of (lwp),

 	  (PTRACE_ARG3_TYPE) 0,

@@ -4856,6 +4921,26 @@

     return 1;

 }

+/* Implement the to_stopped_by_hw_breakpoint target_ops

+   method.  */

+

+static int

+linux_stopped_by_hw_breakpoint (void)

+{

+  struct lwp_info *lwp = get_thread_lwp (current_inferior);

+

+  return lwp->stopped_by_hw_breakpoint;

+}

+

+/* Implement the to_supports_stopped_by_hw_breakpoint target_ops

+   method.  */

+

+static int

+linux_supports_stopped_by_hw_breakpoint (void)

+{

+  return 1; // RHEL

+}

+

 static int

 linux_stopped_by_watchpoint (void)

 {

@@ -5946,6 +6031,8 @@

   linux_read_auxv,

   linux_insert_point,

   linux_remove_point,

+  linux_stopped_by_hw_breakpoint,

+  linux_supports_stopped_by_hw_breakpoint,

   linux_stopped_by_watchpoint,

   linux_stopped_data_address,

 #if defined(__UCLIBC__) && defined(HAS_NOMMU)

Index: gdb-7.6.1/gdb/gdbserver/linux-low.h

===================================================================

--- gdb-7.6.1.orig/gdb/gdbserver/linux-low.h	2016-03-13 21:45:52.861021138 +0100

+++ gdb-7.6.1/gdb/gdbserver/linux-low.h	2016-03-13 21:46:00.668077363 +0100

@@ -223,6 +223,9 @@

      watchpoint trap.  */

   int stopped_by_watchpoint;

+  /* RHEL: TARGET_STOPPED_BY_HW_BREAKPOINT */

+  int stopped_by_hw_breakpoint;

+

   /* On architectures where it is possible to know the data address of

      a triggered watchpoint, STOPPED_DATA_ADDRESS is non-zero, and

      contains such data address.  Only valid if STOPPED_BY_WATCHPOINT