[binutils-gdb] Use signal information to determine SIGTRAP type for FreeBSD.

[John Baldwin <jhb at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=7efba073e2b83803a47fd89e701fe60b98f2debc

commit 7efba073e2b83803a47fd89e701fe60b98f2debc
Author: John Baldwin <jhb@FreeBSD.org>
Date:   Sat Mar 3 21:25:33 2018 -0800

    Use signal information to determine SIGTRAP type for FreeBSD.
    
    Use the signal code from siginfo_t to distinguish SIGTRAP events due
    to trace traps (TRAP_TRACE) and software breakpoints (TRAP_BRKPT).
    For software breakpoints, adjust the PC when the event is reported as
    part of the API when supplying "stopped_by_sw_breakpoint".  Currently
    FreeBSD only supports hardware watchpoints and breakpoints on x86
    which are reported as trace traps.  Signal information is not used on
    MIPS and sparc64 kernels which do not reliably report TRAP_BRKPT for
    software breakpoints.
    
    gdb/ChangeLog:
    
    	* fbsd-nat.c: Include "inf-ptrace.h".
    	(USE_SIGTRAP_SIGINFO): Conditionally define.
    	[USE_SIGTRAP_SIGINFO] (fbsd_handle_debug_trap): New function.
    	(fbsd_wait) [USE_SIGTRAP_SIGINFO]: Call "fbsd_handle_debug_trap".
    	[USE_SIGTRAP_SIGINFO] (fbsd_stopped_by_sw_breakpoint): New
    	function.
    	[USE_SIGTRAP_SIGINFO] (fbsd_supports_stopped_by_sw_breakpoint):
    	Likewise.
    	[USE_SIGTRAP_SIGINFO] (fbsd_supports_stopped_by_hw_breakpoint):
    	Likewise.
    	(fbsd_nat_add_target) [USE_SIGTRAP_SIGINFO]: Set
    	"stopped_by_sw_breakpoint", "supports_stopped_by_sw_breakpoint",
    	"supports_stopped_by_hw_breakpoint" target methods.

Diff:
---
 gdb/ChangeLog  |  16 +++++++++
 gdb/fbsd-nat.c | 107 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 123 insertions(+)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 9a12a5e..1190e0f 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,21 @@
 2018-03-04  John Baldwin  <jhb@FreeBSD.org>
 
+	* fbsd-nat.c: Include "inf-ptrace.h".
+	(USE_SIGTRAP_SIGINFO): Conditionally define.
+	[USE_SIGTRAP_SIGINFO] (fbsd_handle_debug_trap): New function.
+	(fbsd_wait) [USE_SIGTRAP_SIGINFO]: Call "fbsd_handle_debug_trap".
+	[USE_SIGTRAP_SIGINFO] (fbsd_stopped_by_sw_breakpoint): New
+	function.
+	[USE_SIGTRAP_SIGINFO] (fbsd_supports_stopped_by_sw_breakpoint):
+	Likewise.
+	[USE_SIGTRAP_SIGINFO] (fbsd_supports_stopped_by_hw_breakpoint):
+	Likewise.
+	(fbsd_nat_add_target) [USE_SIGTRAP_SIGINFO]: Set
+	"stopped_by_sw_breakpoint", "supports_stopped_by_sw_breakpoint",
+	"supports_stopped_by_hw_breakpoint" target methods.
+
+2018-03-04  John Baldwin  <jhb@FreeBSD.org>
+
 	* NEWS (Changes since GDB 8.1): Add "set/show debug fbsd-nat".
 	* fbsd-nat.c (debug_fbsd_nat): New variable.
 	(show_fbsd_nat_debug): New function.
diff --git a/gdb/fbsd-nat.c b/gdb/fbsd-nat.c
index 2516ac5..bea7f42 100644
--- a/gdb/fbsd-nat.c
+++ b/gdb/fbsd-nat.c
@@ -26,6 +26,7 @@
 #include "gdbcmd.h"
 #include "gdbthread.h"
 #include "gdb_wait.h"
+#include "inf-ptrace.h"
 #include <sys/types.h>
 #include <sys/procfs.h>
 #include <sys/ptrace.h>
@@ -45,6 +46,14 @@
 
 #include <list>
 
+#ifdef TRAP_BRKPT
+/* MIPS does not set si_code for SIGTRAP.  sparc64 reports
+   non-standard values in si_code for SIGTRAP.  */
+# if !defined(__mips__) && !defined(__sparc64__)
+#  define USE_SIGTRAP_SIGINFO
+# endif
+#endif
+
 /* Return the name of a file that can be opened to get the symbols for
    the child process identified by PID.  */
 
@@ -1187,6 +1196,56 @@ fbsd_resume (struct target_ops *ops,
   super_resume (ops, ptid, step, signo);
 }
 
+#ifdef USE_SIGTRAP_SIGINFO
+/* Handle breakpoint and trace traps reported via SIGTRAP.  If the
+   trap was a breakpoint or trace trap that should be reported to the
+   core, return true.  */
+
+static bool
+fbsd_handle_debug_trap (struct target_ops *ops, ptid_t ptid,
+			const struct ptrace_lwpinfo &pl)
+{
+
+  /* Ignore traps without valid siginfo or for signals other than
+     SIGTRAP.  */
+  if (! (pl.pl_flags & PL_FLAG_SI) || pl.pl_siginfo.si_signo != SIGTRAP)
+    return false;
+
+  /* Trace traps are either a single step or a hardware watchpoint or
+     breakpoint.  */
+  if (pl.pl_siginfo.si_code == TRAP_TRACE)
+    {
+      if (debug_fbsd_nat)
+	fprintf_unfiltered (gdb_stdlog,
+			    "FNAT: trace trap for LWP %ld\n", ptid.lwp ());
+      return true;
+    }
+
+  if (pl.pl_siginfo.si_code == TRAP_BRKPT)
+    {
+      /* Fixup PC for the software breakpoint.  */
+      struct regcache *regcache = get_thread_regcache (ptid);
+      struct gdbarch *gdbarch = regcache->arch ();
+      int decr_pc = gdbarch_decr_pc_after_break (gdbarch);
+
+      if (debug_fbsd_nat)
+	fprintf_unfiltered (gdb_stdlog,
+			    "FNAT: sw breakpoint trap for LWP %ld\n",
+			    ptid.lwp ());
+      if (decr_pc != 0)
+	{
+	  CORE_ADDR pc;
+
+	  pc = regcache_read_pc (regcache);
+	  regcache_write_pc (regcache, pc - decr_pc);
+	}
+      return true;
+    }
+
+  return false;
+}
+#endif
+
 /* Wait for the child specified by PTID to do something.  Return the
    process ID of the child, or MINUS_ONE_PTID in case of error; store
    the status in *OURSTATUS.  */
@@ -1372,6 +1431,11 @@ fbsd_wait (struct target_ops *ops,
 	    }
 #endif
 
+#ifdef USE_SIGTRAP_SIGINFO
+	  if (fbsd_handle_debug_trap (ops, wptid, pl))
+	    return wptid;
+#endif
+
 	  /* Note that PL_FLAG_SCE is set for any event reported while
 	     a thread is executing a system call in the kernel.  In
 	     particular, signals that interrupt a sleep in a system
@@ -1410,6 +1474,42 @@ fbsd_wait (struct target_ops *ops,
     }
 }
 
+#ifdef USE_SIGTRAP_SIGINFO
+/* Implement the "to_stopped_by_sw_breakpoint" target_ops method.  */
+
+static int
+fbsd_stopped_by_sw_breakpoint (struct target_ops *ops)
+{
+  struct ptrace_lwpinfo pl;
+
+  if (ptrace (PT_LWPINFO, get_ptrace_pid (inferior_ptid), (caddr_t) &pl,
+	      sizeof pl) == -1)
+    return 0;
+
+  return ((pl.pl_flags & PL_FLAG_SI)
+	  && pl.pl_siginfo.si_signo == SIGTRAP
+	  && pl.pl_siginfo.si_code == TRAP_BRKPT);
+}
+
+/* Implement the "to_supports_stopped_by_sw_breakpoint" target_ops
+   method.  */
+
+static int
+fbsd_supports_stopped_by_sw_breakpoint (struct target_ops *ops)
+{
+  return 1;
+}
+
+/* Implement the "to_supports_stopped_by_hw_breakpoint" target_ops
+   method.  */
+
+static int
+fbsd_supports_stopped_by_hw_breakpoint (struct target_ops *ops)
+{
+  return ops->to_stopped_by_hw_breakpoint != NULL;
+}
+#endif
+
 #ifdef TDP_RFPPWAIT
 /* Target hook for follow_fork.  On entry and at return inferior_ptid is
    the ptid of the followed inferior.  */
@@ -1560,6 +1660,13 @@ fbsd_nat_add_target (struct target_ops *t)
   t->to_wait = fbsd_wait;
   t->to_post_startup_inferior = fbsd_post_startup_inferior;
   t->to_post_attach = fbsd_post_attach;
+#ifdef USE_SIGTRAP_SIGINFO
+  t->to_stopped_by_sw_breakpoint = fbsd_stopped_by_sw_breakpoint;
+  t->to_supports_stopped_by_sw_breakpoint
+    = fbsd_supports_stopped_by_sw_breakpoint;
+  t->to_supports_stopped_by_hw_breakpoint
+    = fbsd_supports_stopped_by_hw_breakpoint;
+#endif
 #ifdef TDP_RFPPWAIT
   t->to_follow_fork = fbsd_follow_fork;
   t->to_insert_fork_catchpoint = fbsd_insert_fork_catchpoint;