add a default method for gdbarch_skip_permanent_breakpoint

breakpoint.c uses gdbarch_breakpoint_from_pc to determine whether a
breakpoint location points at a permanent breakpoint:

 static int
 bp_loc_is_permanent (struct bp_location *loc)
 {
 ...
   addr = loc->address;
   bpoint = gdbarch_breakpoint_from_pc (loc->gdbarch, &addr, &len);
 ...
  if (target_read_memory (loc->address, target_mem, len) == 0
      && memcmp (target_mem, bpoint, len) == 0)
    retval = 1;
 ...

So I think we should default the gdbarch_skip_permanent_breakpoint
hook to advancing the PC by the length of the breakpoint instruction,
as determined by gdbarch_breakpoint_from_pc.  I believe that simple
implementation does the right thing for most architectures.  If
there's an oddball architecture where that doesn't work, then it
should override the hook, just like it should be overriding the hook
if there was no default anyway.

The only two implementation of skip_permanent_breakpoint are
i386_skip_permanent_breakpoint, for x86, and
hppa_skip_permanent_breakpoint, for PA-RISC/HP-UX

The x86 implementation is trivial, and can clearly be replaced by the
new default.

I don't know about the HP-UX one though, I know almost nothing about
PA.  It may well be advancing the PC ends up being equivalent.
Otherwise, it must be that "jump $pc_after_bp" doesn't work either...

Tested on x86_64 Fedora 20 native and gdbserver.

gdb/
2014-11-12  Pedro Alves  <palves@redhat.com>

	* arch-utils.c (default_skip_permanent_breakpoint): New function.
	* arch-utils.h (default_skip_permanent_breakpoint): New
	declaration.
	* gdbarch.sh (skip_permanent_breakpoint): Now an 'f' function.
	Install default_skip_permanent_breakpoint as default method.
	* i386-tdep.c (i386_skip_permanent_breakpoint): Delete function.
	(i386_gdbarch_init): Don't install it.
	* infrun.c (resume): Assume there's always a
	gdbarch_skip_permanent_breakpoint implementation.
	* gdbarch.h, gdbarch.c: Regenerate.

1 files changed, 8 insertions, 0 deletions

diff --git a/gdb/arch-utils.h b/gdb/arch-utils.h
index a609662..1f5dd55 100644
--- a/gdb/arch-utils.h
+++ b/gdb/arch-utils.h
@@ -178,4 +178,12 @@ extern int default_insn_is_jump (struct gdbarch *, CORE_ADDR);
 /* Do-nothing version of vsyscall_range.  Returns false.  */
 
 extern int default_vsyscall_range (struct gdbarch *gdbarch, struct mem_range *range);
+
+/* Default way to advance the PC to the next instruction in order to
+   skip a permanent breakpoint.  Increments the PC by the size of a
+   software breakpoint instruction, as determined with
+   gdbarch_breakpoint_from_pc.  This matches how the breakpoints
+   module determines whether a breakpoint is permanent.  */
+extern void default_skip_permanent_breakpoint (struct regcache *regcache);
+
 #endif