gdbserver: handle all eval_result_type values in tracepoint.cc

It was pointed out[1] that after this commit:

  commit 3812b38d8d
  Date:   Thu Oct 20 11:14:33 2022 +0100

      gdbserver: allow agent expressions to fail with invalid memory access

Now that agent expressions might fail with the error
expr_eval_invalid_memory_access, we might overflow the
eval_result_names array in tracepoint.cc.  This is because the
eval_result_names array does not include a string for either
expr_eval_invalid_goto or expr_eval_invalid_memory_access.

I don't know if having expr_eval_invalid_goto missing is also a
problem, but it feels like eval_result_names should just include a
string for every possible error.

I could just add two more strings into the array, but I figure that a
more robust solution will be to move all of the error types, and their
associated strings, into a new ax-result-types.def file, and to then
include this file in both ax.h and tracepoint.cc in order to build
the enum eval_result_type and the eval_result_names string array.
Doing this means it is impossible to have a missing error string in
the future.

[1] https://inbox.sourceware.org/gdb-patches/01059f8a-0e59-55b5-f530-190c26df5ba3@palves.net/

Approved-By: Pedro Alves <pedro@palves.net>

gdbserver/ax-result-types.def

@@ -0,0 +1,44 @@
+/* Agent expression result types.
+
+   Copyright (C) 2023 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/>.  */
+
+/* The AX_RESULT_TYPE macro is used to define a result type that can be
+   generated by agent expression evaluation.  The first macro argument is
+   the name of an enum entry, and the second is a string that describes
+   this result type.  */
+
+AX_RESULT_TYPE (expr_eval_no_error,
+		"terror:no error")
+AX_RESULT_TYPE (expr_eval_empty_expression,
+		"terror:empty expression")
+AX_RESULT_TYPE (expr_eval_empty_stack,
+		"terror:empty stack")
+AX_RESULT_TYPE (expr_eval_stack_overflow,
+		"terror:stack overflow")
+AX_RESULT_TYPE (expr_eval_stack_underflow,
+		"terror:stack underflow")
+AX_RESULT_TYPE (expr_eval_unhandled_opcode,
+		"terror:unhandled opcode")
+AX_RESULT_TYPE (expr_eval_unrecognized_opcode,
+		"terror:unrecognized opcode")
+AX_RESULT_TYPE (expr_eval_divide_by_zero,
+		"terror:divide by zero")
+AX_RESULT_TYPE (expr_eval_invalid_goto,
+		"terror:invalid goto")
+AX_RESULT_TYPE (expr_eval_invalid_memory_access,
+		"terror:invalid memory access")

gdbserver/ax.h

@@ -33,16 +33,9 @@ struct traceframe;
 
 enum eval_result_type
   {
-    expr_eval_no_error,
-    expr_eval_empty_expression,
-    expr_eval_empty_stack,
-    expr_eval_stack_overflow,
-    expr_eval_stack_underflow,
-    expr_eval_unhandled_opcode,
-    expr_eval_unrecognized_opcode,
-    expr_eval_divide_by_zero,
-    expr_eval_invalid_goto,
-    expr_eval_invalid_memory_access
+#define AX_RESULT_TYPE(ENUM,STR) ENUM,
+#include "ax-result-types.def"
+#undef AX_RESULT_TYPE
   };
 
 struct agent_expr

gdbserver/tracepoint.cc

@@ -859,14 +859,9 @@ static struct tracepoint *last_tracepoint;
 
 static const char * const eval_result_names[] =
   {
-    "terror:in the attic",  /* this should never be reported */
-    "terror:empty expression",
-    "terror:empty stack",
-    "terror:stack overflow",
-    "terror:stack underflow",
-    "terror:unhandled opcode",
-    "terror:unrecognized opcode",
-    "terror:divide by zero"
+#define AX_RESULT_TYPE(ENUM,STR) STR,
+#include "ax-result-types.def"
+#undef AX_RESULT_TYPE
   };
 
 #endif