Rework signal frame probing for FreeBSD/x86

- Use signal frame sniffers that look for the signal trampoline
  instruction sequence to detect most signal frames.

- FreeBSD kernels between 9.2 and 10.1 inclusive do not include the
  signal trampoline code in process core dumps.  To detect signal
  frames for core dumps under these kernels, use the
  kern.proc.sigtramp.<pid> sysctl to fetch the location of the signal
  trampoline in the gdb process and assume that PC values within this
  location are signal frames.  This depends on that location being
  identical for all binaries.

gdb/ChangeLog:
2015-02-25  John Baldwin  <jhb@FreeBSD.org>

	* amd64fbsd-nat.c: Include sys/user.h.
	(_initialize_amd64fbsd_nat): Use the KERN_PROC_SIGTRAMP sysctl
	instead of KERN_PS_STRINGS to locate the signal trampoline.
	* i386fbsd-nat.c: Include sys/user.h.
	(_initialize_i386fbsd_nat): Use the KERN_PROC_SIGTRAMP sysctl
	instead of KERN_PS_STRINGS to locate the signal trampoline.
	* amd64fbsd-tdep.c (amd64fbsd_sigtramp_code): New.
	(amd64fbsd_sigtramp_p): New.
	(amd64fbsd_sigtramp_start_addr, amd64fbsd_sigtramp_end_addr): No
	longer set default values.
	(amd64fbsd_init_abi): Set "sigtramp_p" to "amd64fbsd_sigtramp_p".
	* i386fbsd-tdep.c (i386fbsd_sigtramp_start)
	(i386fbsd_sigtramp_middle, i386fbsd_sigtramp_end)
	(i386fbsd_freebsd4_sigtramp_start)
	(i386fbsd_freebsd4_sigtramp_middle)
	(i386fbsd_freebsd4_sigtramp_end, i386fbsd_osigtramp_start)
	(i386fbsd_osigtramp_middle, i386fbsd_osigtramp_end): New.
	(i386fbsd_sigtramp_p): New.
	(i386fbsd_sigtramp_start_addr, i386fbsd_sigtramp_end_addr): No
	longer set default values.
	(i386fbsd_init_abi): Set "sigtramp_p" to "i386fbsd_sigtramp_p".

1 files changed, 21 insertions, 13 deletions

diff --git a/gdb/amd64fbsd-nat.c b/gdb/amd64fbsd-nat.c
index 1c396e2..b1b261c 100644
--- a/gdb/amd64fbsd-nat.c
+++ b/gdb/amd64fbsd-nat.c
@@ -26,6 +26,7 @@
 #include <sys/types.h>
 #include <sys/ptrace.h>
 #include <sys/sysctl.h>
+#include <sys/user.h>
 #include <machine/reg.h>
 
 #include "fbsd-nat.h"
@@ -244,24 +245,31 @@ Please report this to <bug-gdb@gnu.org>."),
 
   SC_RBP_OFFSET = offset;
 
-  /* FreeBSD provides a kern.ps_strings sysctl that we can use to
-     locate the sigtramp.  That way we can still recognize a sigtramp
-     if its location is changed in a new kernel.  Of course this is
-     still based on the assumption that the sigtramp is placed
-     directly under the location where the program arguments and
-     environment can be found.  */
+#ifdef KERN_PROC_SIGTRAMP
+  /* Normally signal frames are detected via amd64fbsd_sigtramp_p.
+     However, FreeBSD 9.2 through 10.1 do not include the page holding
+     the signal code in core dumps.  These releases do provide a
+     kern.proc.sigtramp.<pid> sysctl that returns the location of the
+     signal trampoline for a running process.  We fetch the location
+     of the current (gdb) process and use this to identify signal
+     frames in core dumps from these releases.  Note that this only
+     works for core dumps of 64-bit (FreeBSD/amd64) processes and does
+     not handle core dumps of 32-bit (FreeBSD/i386) processes.  */
   {
-    int mib[2];
-    long ps_strings;
+    int mib[4];
+    struct kinfo_sigtramp kst;
     size_t len;
 
     mib[0] = CTL_KERN;
-    mib[1] = KERN_PS_STRINGS;
-    len = sizeof (ps_strings);
-    if (sysctl (mib, 2, &ps_strings, &len, NULL, 0) == 0)
+    mib[1] = KERN_PROC;
+    mib[2] = KERN_PROC_SIGTRAMP;
+    mib[3] = getpid ();
+    len = sizeof (kst);
+    if (sysctl (mib, 4, &kst, &len, NULL, 0) == 0)
       {
-	amd64fbsd_sigtramp_start_addr = ps_strings - 32;
-	amd64fbsd_sigtramp_end_addr = ps_strings;
+	amd64fbsd_sigtramp_start_addr = (uintptr_t) kst.ksigtramp_start;
+	amd64fbsd_sigtramp_end_addr = (uintptr_t) kst.ksigtramp_end;
       }
   }
+#endif
 }