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.

gdb/ChangeLog

@@ -1,3 +1,16 @@
+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.
+
 2014-11-11  Daniel Colascione  <dancol@dancol.org>
 
 	Warn about cross-PID-namespace debugging.

gdb/arch-utils.c

@@ -826,7 +826,18 @@ int default_insn_is_jump (struct gdbarch *gdbarch, CORE_ADDR addr)
   return 0;
 }
 
-/* */
+void
+default_skip_permanent_breakpoint (struct regcache *regcache)
+{
+  struct gdbarch *gdbarch = get_regcache_arch (regcache);
+  CORE_ADDR current_pc = regcache_read_pc (regcache);
+  const gdb_byte *bp_insn;
+  int bp_len;
+
+  bp_insn = gdbarch_breakpoint_from_pc (gdbarch, &current_pc, &bp_len);
+  current_pc += bp_len;
+  regcache_write_pc (regcache, current_pc);
+}
 
 /* -Wmissing-prototypes */
 extern initialize_file_ftype _initialize_gdbarch_utils;

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

gdb/gdbarch.c

@@ -393,6 +393,7 @@ gdbarch_alloc (const struct gdbarch_info *info,
   gdbarch->elf_make_msymbol_special = default_elf_make_msymbol_special;
   gdbarch->coff_make_msymbol_special = default_coff_make_msymbol_special;
   gdbarch->register_reggroup_p = default_register_reggroup_p;
+  gdbarch->skip_permanent_breakpoint = default_skip_permanent_breakpoint;
   gdbarch->displaced_step_hw_singlestep = default_displaced_step_hw_singlestep;
   gdbarch->displaced_step_fixup = NULL;
   gdbarch->displaced_step_free_closure = NULL;
@@ -581,7 +582,7 @@ verify_gdbarch (struct gdbarch *gdbarch)
   /* Skip verify of gcore_bfd_target, has predicate.  */
   /* Skip verify of vtable_function_descriptors, invalid_p == 0 */
   /* Skip verify of vbit_in_delta, invalid_p == 0 */
-  /* Skip verify of skip_permanent_breakpoint, has predicate.  */
+  /* Skip verify of skip_permanent_breakpoint, invalid_p == 0 */
   /* Skip verify of max_insn_length, has predicate.  */
   /* Skip verify of displaced_step_copy_insn, has predicate.  */
   /* Skip verify of displaced_step_hw_singlestep, invalid_p == 0 */
@@ -1189,9 +1190,6 @@ gdbarch_dump (struct gdbarch *gdbarch, struct ui_file *file)
   fprintf_unfiltered (file,
                       "gdbarch_dump: skip_main_prologue = <%s>\n",
                       host_address_to_string (gdbarch->skip_main_prologue));
-  fprintf_unfiltered (file,
-                      "gdbarch_dump: gdbarch_skip_permanent_breakpoint_p() = %d\n",
-                      gdbarch_skip_permanent_breakpoint_p (gdbarch));
   fprintf_unfiltered (file,
                       "gdbarch_dump: skip_permanent_breakpoint = <%s>\n",
                       host_address_to_string (gdbarch->skip_permanent_breakpoint));
@@ -3465,13 +3463,6 @@ set_gdbarch_vbit_in_delta (struct gdbarch *gdbarch,
   gdbarch->vbit_in_delta = vbit_in_delta;
 }
 
-int
-gdbarch_skip_permanent_breakpoint_p (struct gdbarch *gdbarch)
-{
-  gdb_assert (gdbarch != NULL);
-  return gdbarch->skip_permanent_breakpoint != NULL;
-}
-
 void
 gdbarch_skip_permanent_breakpoint (struct gdbarch *gdbarch, struct regcache *regcache)
 {

gdb/gdbarch.h

@@ -829,8 +829,6 @@ extern void set_gdbarch_vbit_in_delta (struct gdbarch *gdbarch, int vbit_in_delt
 
 /* Advance PC to next instruction in order to skip a permanent breakpoint. */
 
-extern int gdbarch_skip_permanent_breakpoint_p (struct gdbarch *gdbarch);
-
 typedef void (gdbarch_skip_permanent_breakpoint_ftype) (struct regcache *regcache);
 extern void gdbarch_skip_permanent_breakpoint (struct gdbarch *gdbarch, struct regcache *regcache);
 extern void set_gdbarch_skip_permanent_breakpoint (struct gdbarch *gdbarch, gdbarch_skip_permanent_breakpoint_ftype *skip_permanent_breakpoint);

gdb/gdbarch.sh

@@ -699,7 +699,7 @@ v:int:vtable_function_descriptors:::0:0::0
 v:int:vbit_in_delta:::0:0::0
 
 # Advance PC to next instruction in order to skip a permanent breakpoint.
-F:void:skip_permanent_breakpoint:struct regcache *regcache:regcache
+f:void:skip_permanent_breakpoint:struct regcache *regcache:regcache:default_skip_permanent_breakpoint:default_skip_permanent_breakpoint::0
 
 # The maximum length of an instruction on this architecture in bytes.
 V:ULONGEST:max_insn_length:::0:0

gdb/i386-tdep.c

@@ -4523,18 +4523,6 @@ i386_fetch_pointer_argument (struct frame_info *frame, int argi,
   return read_memory_unsigned_integer (sp + (4 * (argi + 1)), 4, byte_order);
 }
 
-static void
-i386_skip_permanent_breakpoint (struct regcache *regcache)
-{
-  CORE_ADDR current_pc = regcache_read_pc (regcache);
-
- /* On i386, breakpoint is exactly 1 byte long, so we just
-    adjust the PC in the regcache.  */
-  current_pc += 1;
-  regcache_write_pc (regcache, current_pc);
-}
-
-
 #define PREFIX_REPZ	0x01
 #define PREFIX_REPNZ	0x02
 #define PREFIX_LOCK	0x04
@@ -8566,9 +8554,6 @@ i386_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
     set_gdbarch_iterate_over_regset_sections
       (gdbarch, i386_iterate_over_regset_sections);
 
-  set_gdbarch_skip_permanent_breakpoint (gdbarch,
-					 i386_skip_permanent_breakpoint);
-
   set_gdbarch_fast_tracepoint_valid_at (gdbarch,
 					i386_fast_tracepoint_valid_at);
 

gdb/infrun.c

@@ -2075,13 +2075,7 @@ resume (int step, enum gdb_signal sig)
      breakpoints can't be removed.  So we have to test for it here.  */
   if (breakpoint_here_p (aspace, pc) == permanent_breakpoint_here)
     {
-      if (gdbarch_skip_permanent_breakpoint_p (gdbarch))
       gdbarch_skip_permanent_breakpoint (gdbarch, regcache);
-      else
-	error (_("\
-The program is stopped at a permanent breakpoint, but GDB does not know\n\
-how to step past a permanent breakpoint on this architecture.  Try using\n\
-a command like `return' or `jump' to continue execution."));
     }
 
   /* If we have a breakpoint to step over, make sure to do a single