On i386, use PCB_SAVECTX flags to distinguish between state saved by a normal

context switch, and state saved by savectx().  This makes backtraces from
kernel crash dumps work much better.

2 files changed, 73 insertions, 2 deletions

diff --git a/gnu/usr.bin/binutils/gdb/config/i386/obsd.mh b/gnu/usr.bin/binutils/gdb/config/i386/obsd.mh
index f5b4b2dffc7..3bdd4c12a9b 100644
--- a/gnu/usr.bin/binutils/gdb/config/i386/obsd.mh
+++ b/gnu/usr.bin/binutils/gdb/config/i386/obsd.mh
@@ -1,6 +1,6 @@
 # Host: OpenBSD/i386 ELF
 NATDEPFILES= fork-child.o inf-ptrace.o \
-	i386bsd-nat.o i386obsd-nat.o i386nbsd-nat.o bsd-kvm.o
+	i386bsd-nat.o i386obsd-nat.o bsd-kvm.o
 NAT_FILE= nm-obsd.h
 
 LOADLIBES= -lkvm
diff --git a/gnu/usr.bin/binutils/gdb/i386obsd-nat.c b/gnu/usr.bin/binutils/gdb/i386obsd-nat.c
index 68cc79044ec..892b17b71eb 100644
--- a/gnu/usr.bin/binutils/gdb/i386obsd-nat.c
+++ b/gnu/usr.bin/binutils/gdb/i386obsd-nat.c
@@ -20,11 +20,76 @@
    Boston, MA 02111-1307, USA.  */
 
 #include "defs.h"
+#include "gdbcore.h"
+#include "regcache.h"
+#include "target.h"
+
+#include "i386-tdep.h"
+#include "i386bsd-nat.h"
 
 #include <sys/param.h>
 #include <sys/sysctl.h>
 
-#include "i386-tdep.h"
+/* Support for debugging kernel virtual memory images.  */
+
+#include <machine/frame.h>
+#include <machine/pcb.h>
+
+#include "bsd-kvm.h"
+
+static int
+i386obsd_supply_pcb (struct regcache *regcache, struct pcb *pcb)
+{
+  struct switchframe sf;
+
+  /* The following is true for OpenBSD 4.3:
+
+     The pcb contains %esp and %ebp at the point of the context switch
+     in cpu_switchto().  At that point we have a stack frame as
+     described by `struct switchframe', which for OpenBSD 4.3 has the
+     following layout:
+
+     %edi
+     %esi
+     %ebx
+     %eip
+
+     we reconstruct the register state as it would look when we just
+     returned from cpu_switchto().
+
+     For crash dumps, the state is saved by savectx().  In that case
+     we just reconstruct the register state as if we just returned
+     from dumsys().  */
+
+  /* The stack pointer shouldn't be zero.  */
+  if (pcb->pcb_esp == 0)
+    return 0;
+
+  if ((pcb->pcb_flags & PCB_SAVECTX) == 0)
+    {
+      /* Yes, we have a frame that matches cpu_switchto().  */
+      read_memory (pcb->pcb_esp, (char *) &sf, sizeof sf);
+      pcb->pcb_esp += sizeof (struct switchframe);
+      regcache_raw_supply (regcache, I386_EDI_REGNUM, &sf.sf_edi);
+      regcache_raw_supply (regcache, I386_ESI_REGNUM, &sf.sf_esi);
+      regcache_raw_supply (regcache, I386_EBX_REGNUM, &sf.sf_ebx);
+      regcache_raw_supply (regcache, I386_EIP_REGNUM, &sf.sf_eip);
+    }
+  else
+    {
+      /* No, the pcb must have been last updated by savectx().  */
+      pcb->pcb_esp = pcb->pcb_ebp;
+      pcb->pcb_ebp = read_memory_integer(pcb->pcb_esp, 4);
+      sf.sf_eip = read_memory_integer(pcb->pcb_esp + 4, 4);
+      regcache_raw_supply (regcache, I386_EIP_REGNUM, &sf.sf_eip);
+    }
+
+  regcache_raw_supply (regcache, I386_EBP_REGNUM, &pcb->pcb_ebp);
+  regcache_raw_supply (regcache, I386_ESP_REGNUM, &pcb->pcb_esp);
+
+  return 1;
+}
+
 
 /* Prevent warning from -Wmissing-prototypes.  */
 void _initialize_i386obsd_nat (void);
@@ -57,4 +122,10 @@ _initialize_i386obsd_nat (void)
       }
   }
 #endif
+
+  /* We've got nothing to add to the common *BSD/i386 target.  */
+  add_target (i386bsd_target ());
+
+  /* Support debugging kernel virtual memory images.  */
+  bsd_kvm_add_target (i386obsd_supply_pcb);
 }