Fix another crash with gdb parameters in Python

While looking into the language-capturing issue, I found another way
to crash gdb using parameters from Python:

(gdb) python print(gdb.parameter('endian'))

(This is related to PR python/12188, though this patch isn't going to
fix what that bug is really about.)

The problem here is that the global variable that underlies the
"endian" parameter is initialized to NULL.  However, that's not a
valid value for an "enum" set/show parameter.

My understanding is that, in gdb, an "enum" parameter's underlying
variable must have a value that is "==" (not just strcmp-equal) to one
of the values coming from the enum array.  This invariant is relied on
in various places.

I started this patch by fixing the problem with "endian".  Then I
added some assertions to add_setshow_enum_cmd to try to catch other
problems of the same type.

This patch fixes all the problems that I found.  I also looked at all
the calls to add_setshow_enum_cmd to ensure that they were all
included in the gdb I tested.  I think they are: there are no calls in
nat-* files, or in remote-sim.c; and I was trying a build with all
targets, Python, and Guile enabled.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=12188

9 files changed, 41 insertions, 12 deletions

diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c
index 38e3132..3ee978a 100644
--- a/gdb/arch-utils.c
+++ b/gdb/arch-utils.c
@@ -359,7 +359,7 @@ static const char *const endian_enum[] =
   endian_auto,
   NULL,
 };
-static const char *set_endian_string;
+static const char *set_endian_string = endian_auto;
 
 enum bfd_endian
 selected_byte_order (void)
@@ -757,7 +757,8 @@ initialize_current_architecture (void)
      list of architectures.  */
   {
     /* Append ``auto''.  */
-    arches.push_back ("auto");
+    set_architecture_string = "auto";
+    arches.push_back (set_architecture_string);
     arches.push_back (nullptr);
     set_show_commands architecture_cmds
       = add_setshow_enum_cmd ("architecture", class_support,
diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
index f6bd76a..f46913e 100644
--- a/gdb/arm-tdep.c
+++ b/gdb/arm-tdep.c
@@ -9802,6 +9802,8 @@ _initialize_arm_tdep ()
 	size_t offset = strlen ("reg-names-");
 	const char *style = disasm_options->name[i];
 	valid_disassembly_styles[j++] = &style[offset];
+	if (strcmp (&style[offset], "std") == 0)
+	  disassembly_style = &style[offset];
 	length = snprintf (rdptr, rest, "%s - %s\n", &style[offset],
 			   disasm_options->description[i]);
 	rdptr += length;
diff --git a/gdb/charset.c b/gdb/charset.c
index 9b1de08..bf205ae 100644
--- a/gdb/charset.c
+++ b/gdb/charset.c
@@ -1029,6 +1029,9 @@ _initialize_charset ()
 #endif
 #endif
 
+  /* Recall that the first element is always "auto".  */
+  host_charset_name = charset_enum[0];
+  gdb_assert (strcmp (host_charset_name, "auto") == 0);
   add_setshow_enum_cmd ("charset", class_support,
 			charset_enum, &host_charset_name, _("\
 Set the host and target character sets."), _("\
@@ -1057,6 +1060,9 @@ To see a list of the character sets GDB supports, type `set host-charset <TAB>'.
 			show_host_charset_name,
 			&setlist, &showlist);
 
+  /* Recall that the first element is always "auto".  */
+  target_charset_name = charset_enum[0];
+  gdb_assert (strcmp (target_charset_name, "auto") == 0);
   add_setshow_enum_cmd ("target-charset", class_support,
 			charset_enum, &target_charset_name, _("\
 Set the target character set."), _("\
@@ -1069,6 +1075,9 @@ To see a list of the character sets GDB supports, type `set target-charset'<TAB>
 			show_target_charset_name,
 			&setlist, &showlist);
 
+  /* Recall that the first element is always "auto".  */
+  target_wide_charset_name = charset_enum[0];
+  gdb_assert (strcmp (target_wide_charset_name, "auto") == 0);
   add_setshow_enum_cmd ("target-wide-charset", class_support,
 			charset_enum, &target_wide_charset_name,
 			_("\
diff --git a/gdb/cli/cli-decode.c b/gdb/cli/cli-decode.c
index c8cd956..5d94030 100644
--- a/gdb/cli/cli-decode.c
+++ b/gdb/cli/cli-decode.c
@@ -613,6 +613,16 @@ add_setshow_enum_cmd (const char *name,
 		      struct cmd_list_element **set_list,
 		      struct cmd_list_element **show_list)
 {
+  /* We require *VAR to be initialized before this call, and
+     furthermore it must be == to one of the values in ENUMLIST.  */
+  gdb_assert (var != nullptr && *var != nullptr);
+  for (int i = 0; ; ++i)
+    {
+      gdb_assert (enumlist[i] != nullptr);
+      if (*var == enumlist[i])
+	break;
+    }
+
   set_show_commands commands
     =  add_setshow_cmd_full<const char *> (name, theclass, var_enum, var,
 					   set_doc, show_doc, help_doc,
diff --git a/gdb/guile/scm-param.c b/gdb/guile/scm-param.c
index 2bbd463..42727bb 100644
--- a/gdb/guile/scm-param.c
+++ b/gdb/guile/scm-param.c
@@ -458,12 +458,12 @@ add_setshow_generic (enum var_types param_type, enum command_class cmd_class,
       break;
 
     case var_enum:
+      /* Initialize the value, just in case.  */
+      make_setting (self).set<const char *> (self->enumeration[0]);
       commands = add_setshow_enum_cmd (cmd_name, cmd_class, self->enumeration,
 				       &self->value.cstringval, set_doc,
 				       show_doc, help_doc, set_func, show_func,
 				       set_list, show_list);
-      /* Initialize the value, just in case.  */
-      make_setting (self).set<const char *> (self->enumeration[0]);
       break;
 
     default:
diff --git a/gdb/language.c b/gdb/language.c
index 0846b3e..f000142 100644
--- a/gdb/language.c
+++ b/gdb/language.c
@@ -476,7 +476,8 @@ add_set_language_command ()
   /* Display "auto", "local" and "unknown" first, and then the rest,
      alpha sorted.  */
   const char **language_names_p = language_names;
-  *language_names_p++ = language_def (language_auto)->name ();
+  language = language_def (language_auto)->name ();
+  *language_names_p++ = language;
   *language_names_p++ = "local";
   *language_names_p++ = language_def (language_unknown)->name ();
   const char **sort_begin = language_names_p;
@@ -1150,6 +1151,8 @@ _initialize_language ()
   add_alias_cmd ("c", setshow_check_cmds.show, no_class, 1, &showlist);
   add_alias_cmd ("ch", setshow_check_cmds.show, no_class, 1, &showlist);
 
+  range = type_or_range_names[3];
+  gdb_assert (strcmp (range, "auto") == 0);
   add_setshow_enum_cmd ("range", class_support, type_or_range_names,
 			&range,
 			_("Set range checking (on/warn/off/auto)."),
@@ -1158,6 +1161,8 @@ _initialize_language ()
 			show_range_command,
 			&setchecklist, &showchecklist);
 
+  case_sensitive = case_sensitive_names[2];
+  gdb_assert (strcmp (case_sensitive, "auto") == 0);
   add_setshow_enum_cmd ("case-sensitive", class_support, case_sensitive_names,
 			&case_sensitive, _("\
 Set case sensitivity in name search (on/off/auto)."), _("\
@@ -1174,10 +1179,6 @@ For Fortran the default is off; for other languages the default is on."),
 
   add_set_language_command ();
 
-  language = "auto";
-  range = "auto";
-  case_sensitive = "auto";
-
   /* Have the above take effect.  */
   set_language (language_auto);
 }
diff --git a/gdb/osabi.c b/gdb/osabi.c
index 40c86e7..d4a9806 100644
--- a/gdb/osabi.c
+++ b/gdb/osabi.c
@@ -666,11 +666,13 @@ _initialize_gdb_osabi ()
 				  generic_elf_osabi_sniffer);
 
   /* Register the "set osabi" command.  */
+  user_osabi_state = osabi_auto;
+  set_osabi_string = gdb_osabi_available_names[0];
+  gdb_assert (strcmp (set_osabi_string, "auto") == 0);
   add_setshow_enum_cmd ("osabi", class_support, gdb_osabi_available_names,
 			&set_osabi_string,
 			_("Set OS ABI of target."),
 			_("Show OS ABI of target."),
 			NULL, set_osabi, show_osabi,
 			&setlist, &showlist);
-  user_osabi_state = osabi_auto;
 }
diff --git a/gdb/python/py-param.c b/gdb/python/py-param.c
index 24678bc..f5f0eca 100644
--- a/gdb/python/py-param.c
+++ b/gdb/python/py-param.c
@@ -572,13 +572,13 @@ add_setshow_generic (int parmclass, enum command_class cmdclass,
       break;
 
     case var_enum:
+      /* Initialize the value, just in case.  */
+      self->value.cstringval = self->enumeration[0];
       commands = add_setshow_enum_cmd (cmd_name.get (), cmdclass,
 				       self->enumeration,
 				       &self->value.cstringval, set_doc,
 				       show_doc, help_doc, get_set_value,
 				       get_show_value, set_list, show_list);
-      /* Initialize the value, just in case.  */
-      self->value.cstringval = self->enumeration[0];
       break;
 
     default:
diff --git a/gdb/testsuite/gdb.python/py-parameter.exp b/gdb/testsuite/gdb.python/py-parameter.exp
index b025c25..2de148c 100644
--- a/gdb/testsuite/gdb.python/py-parameter.exp
+++ b/gdb/testsuite/gdb.python/py-parameter.exp
@@ -364,3 +364,7 @@ test_really_undocumented_parameter
 test_deprecated_api_parameter
 test_integer_parameter
 test_throwing_parameter
+
+# This caused a gdb crash.
+gdb_test "python print(gdb.parameter('endian'))" "auto" \
+    "print endian parameter"