[PATCH 2/3] gdb: remove gdbarch_displaced_step_fixup_p

[Andrew Burgess <aburgess@redhat.com>]

The comment on the gdbarch_displaced_step_fixup gdbarch method
indicates that this method is optional and that GDB will perform some
default if this method is not supplied.  As such we define a predicate
gdbarch_displaced_step_fixup_p.

It may have been true at one point that the fixup method was optional,
but it is no longer true.  If this method is not defined and GDB tries
to complete a displaced step, then GDB is going to crash.

Additionally the gdbarch_displaced_step_fixup_p predicate is not used
anywhere in GDB.

In this commit I have removed the gdbarch_displaced_step_fixup_p
predicate, and I have updated the validation check for the
gdbarch_displaced_step_fixup method; if the
gdbarch_displaced_step_copy_insn method is defined then the fixup
method must also be defined.

I believe I've manually checked all the current places where
gdbarch_displaced_step_copy_insn is defined and they all also define
the fixup method, so this change should cause no problems for anyone.

There should be no user visible changes after this commit.
---
 gdb/gdbarch-components.py |  4 ++--
 gdb/gdbarch-gen.h         |  2 --
 gdb/gdbarch.c             | 14 ++------------
 3 files changed, 4 insertions(+), 16 deletions(-)

diff --git a/gdb/gdbarch-components.py b/gdb/gdbarch-components.py
index 76ad2832d8a..06be4b57051 100644
--- a/gdb/gdbarch-components.py
+++ b/gdb/gdbarch-components.py
@@ -1851,9 +1851,9 @@ see the comments in infrun.c.
         ("CORE_ADDR", "to"),
         ("struct regcache *", "regs"),
     ],
-    predicate=True,
+    predicate=False,
     predefault="NULL",
-    invalid=True,
+    invalid="(gdbarch->displaced_step_copy_insn == nullptr) != (gdbarch->displaced_step_fixup == nullptr)",
 )
 
 Method(
diff --git a/gdb/gdbarch-gen.h b/gdb/gdbarch-gen.h
index 32b2d96fbe0..ac63e84b191 100644
--- a/gdb/gdbarch-gen.h
+++ b/gdb/gdbarch-gen.h
@@ -1085,8 +1085,6 @@ extern void set_gdbarch_displaced_step_hw_singlestep (struct gdbarch *gdbarch, g
    For a general explanation of displaced stepping and how GDB uses it,
    see the comments in infrun.c. */
 
-extern bool gdbarch_displaced_step_fixup_p (struct gdbarch *gdbarch);
-
 typedef void (gdbarch_displaced_step_fixup_ftype) (struct gdbarch *gdbarch, struct displaced_step_copy_insn_closure *closure, CORE_ADDR from, CORE_ADDR to, struct regcache *regs);
 extern void gdbarch_displaced_step_fixup (struct gdbarch *gdbarch, struct displaced_step_copy_insn_closure *closure, CORE_ADDR from, CORE_ADDR to, struct regcache *regs);
 extern void set_gdbarch_displaced_step_fixup (struct gdbarch *gdbarch, gdbarch_displaced_step_fixup_ftype *displaced_step_fixup);
diff --git a/gdb/gdbarch.c b/gdb/gdbarch.c
index 04fcc92f8f9..4958d3c5fc6 100644
--- a/gdb/gdbarch.c
+++ b/gdb/gdbarch.c
@@ -447,7 +447,8 @@ verify_gdbarch (struct gdbarch *gdbarch)
   /* 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 */
-  /* Skip verify of displaced_step_fixup, has predicate.  */
+  if ((gdbarch->displaced_step_copy_insn == nullptr) != (gdbarch->displaced_step_fixup == nullptr))
+    log.puts ("\n\tdisplaced_step_fixup");
   /* Skip verify of displaced_step_prepare, has predicate.  */
   if ((! gdbarch->displaced_step_finish) != (! gdbarch->displaced_step_prepare))
     log.puts ("\n\tdisplaced_step_finish");
@@ -1087,9 +1088,6 @@ gdbarch_dump (struct gdbarch *gdbarch, struct ui_file *file)
   gdb_printf (file,
 	      "gdbarch_dump: displaced_step_hw_singlestep = <%s>\n",
 	      host_address_to_string (gdbarch->displaced_step_hw_singlestep));
-  gdb_printf (file,
-	      "gdbarch_dump: gdbarch_displaced_step_fixup_p() = %d\n",
-	      gdbarch_displaced_step_fixup_p (gdbarch));
   gdb_printf (file,
 	      "gdbarch_dump: displaced_step_fixup = <%s>\n",
 	      host_address_to_string (gdbarch->displaced_step_fixup));
@@ -4046,19 +4044,11 @@ set_gdbarch_displaced_step_hw_singlestep (struct gdbarch *gdbarch,
   gdbarch->displaced_step_hw_singlestep = displaced_step_hw_singlestep;
 }
 
-bool
-gdbarch_displaced_step_fixup_p (struct gdbarch *gdbarch)
-{
-  gdb_assert (gdbarch != NULL);
-  return gdbarch->displaced_step_fixup != NULL;
-}
-
 void
 gdbarch_displaced_step_fixup (struct gdbarch *gdbarch, struct displaced_step_copy_insn_closure *closure, CORE_ADDR from, CORE_ADDR to, struct regcache *regs)
 {
   gdb_assert (gdbarch != NULL);
   gdb_assert (gdbarch->displaced_step_fixup != NULL);
-  /* Do not check predicate: gdbarch->displaced_step_fixup != NULL, allow call.  */
   if (gdbarch_debug >= 2)
     gdb_printf (gdb_stdlog, "gdbarch_displaced_step_fixup called\n");
   gdbarch->displaced_step_fixup (gdbarch, closure, from, to, regs);
-- 
2.25.4