gdb: introduce status enum for displaced step prepare/finish

This is a preparatory patch to reduce the size of the diff of the
upcoming main patch.  It introduces enum types for the return values of
displaced step "prepare" and "finish" operations.  I find that this
expresses better the intention of the code, rather than returning
arbitrary integer values (-1, 0 and 1) which are difficult to remember.
That makes the code easier to read.

I put the new enum types in a new displaced-stepping.h file, because I
introduce that file in a later patch anyway.  Putting it there avoids
having to move it later.

There is one change in behavior for displaced_step_finish: it currently
returns 0 if the thread wasn't doing a displaced step and 1 if the
thread was doing a displaced step which was executed successfully.  It
turns out that this distinction is not needed by any caller, so I've
merged these two cases into "_OK", rather than adding an extra
enumerator.

gdb/ChangeLog:

	* infrun.c (displaced_step_prepare_throw): Change return type to
	displaced_step_prepare_status.
	(displaced_step_prepare): Likewise.
	(displaced_step_finish): Change return type to
	displaced_step_finish_status.
	(resume_1): Adjust.
	(stop_all_threads): Adjust.
	* displaced-stepping.h: New file.

Change-Id: I5c8fe07212cd398d5b486b5936d9d0807acd3788

1 files changed, 47 insertions, 0 deletions

diff --git a/gdb/displaced-stepping.h b/gdb/displaced-stepping.h
new file mode 100644
index 00000000000..44aca74111d
--- /dev/null
+++ b/gdb/displaced-stepping.h
@@ -0,0 +1,47 @@
+/* Displaced stepping related things.
+
+   Copyright (C) 2020 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef DISPLACED_STEPPING_H
+#define DISPLACED_STEPPING_H
+
+enum displaced_step_prepare_status
+{
+  /* A displaced stepping buffer was successfully allocated and prepared.  */
+  DISPLACED_STEP_PREPARE_STATUS_OK,
+
+  /* This particular instruction can't be displaced stepped, GDB should fall
+     back on in-line stepping.  */
+  DISPLACED_STEP_PREPARE_STATUS_CANT,
+
+  /* Not enough resources are available at this time, try again later.  */
+  DISPLACED_STEP_PREPARE_STATUS_UNAVAILABLE,
+};
+
+enum displaced_step_finish_status
+{
+  /* Either the instruction was stepped and fixed up, or the specified thread
+     wasn't executing a displaced step (in which case there's nothing to
+     finish). */
+  DISPLACED_STEP_FINISH_STATUS_OK,
+
+  /* The thread started a displaced step, but didn't complete it.  */
+  DISPLACED_STEP_FINISH_STATUS_NOT_EXECUTED,
+};
+
+#endif /* DISPLACED_STEPPING_H */