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authorAndrew Burgess <aburgess@redhat.com>2025-06-03 17:23:10 +0100
committerAndrew Burgess <aburgess@redhat.com>2025-06-04 09:39:33 +0100
commitf84a4db958af0ee1521acdf69eb2be38ea2e66a3 (patch)
tree4217ea7569d4b9e5be3149fa41dafee590fd29c3 /gdb/guile/scm-cmd.c
parent4c1459870634074ea2266ec5755371eec3948963 (diff)
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gdb/python/guile: fix segfault from nested prefix command creation
A commit I recently pushed: commit 0b5023cc71d3af8b18e10e6599a3f9381bc15265 Date: Sat Apr 12 09:15:53 2025 +0100 gdb/python/guile: user created prefix commands get help list can trigger a segfault if a user tries to create nested prefix commands. For example, this will trigger a crash: (gdb) python gdb.ParameterPrefix("prefix-1", gdb.COMMAND_NONE) (gdb) python gdb.ParameterPrefix("prefix-1 prefix-2", gdb.COMMAND_NONE) Fatal signal: Segmentation fault ... etc ... If the user adds an actual parameter under 'prefix-1' before creating 'prefix-2', then everything is fine: (gdb) python gdb.ParameterPrefix("prefix-1", gdb.COMMAND_NONE) (gdb) python gdb.Parameter('prefix-1 param-1', gdb.COMMAND_NONE, gdb.PARAM_BOOLEAN) (gdb) python gdb.ParameterPrefix("prefix-1 prefix-2", gdb.COMMAND_NONE) The mistake in the above patch is in how gdbpy_parse_command_name is used. The BASE_LIST output argument from this function points to the list of commands for the prefix, not to the prefix command itself. So when gdbpy_parse_command_name is called for 'prefix-1 prefix-2', BASE_LIST points to the list of commands associated with 'prefix-1', not to the actual 'prefix-1' cmd_list_element. Back in cmdpy_init, from where gdbpy_parse_command_name was called, I was walking back from the first entry in BASE_LIST to figure out if this was a "show" prefix command or not. However, if BASE_LIST is empty then there is no first item, and this would trigger the segfault. The solution it to extend gdbpy_parse_command_name to also return the prefix cmd_list_element in addition to the existing values. With this done, and cmdpy_init updated, the segfault is now avoided. There's a new test that would trigger the crash without the patch. And, of course, the above commit also broke guile in the exact same way. And the fix is exactly the same. And there's a guile test too. NOTE: We should investigate possibly sharing some of this boiler plate helper code between Python and Guile. But not in this commit. Approved-By: Tom Tromey <tom@tromey.com>
Diffstat (limited to 'gdb/guile/scm-cmd.c')
-rw-r--r--gdb/guile/scm-cmd.c30
1 files changed, 21 insertions, 9 deletions
diff --git a/gdb/guile/scm-cmd.c b/gdb/guile/scm-cmd.c
index 565d588..74646f3 100644
--- a/gdb/guile/scm-cmd.c
+++ b/gdb/guile/scm-cmd.c
@@ -457,11 +457,13 @@ cmdscm_completer (struct cmd_list_element *command,
name of the new command. All earlier words must be existing prefix
commands.
- *BASE_LIST is set to the final prefix command's list of
- *sub-commands.
+ *BASE_LIST is set to the final prefix command's list of sub-commands.
START_LIST is the list in which the search starts.
+ When PREFIX_CMD is not NULL then *PREFIX_CMD is set to the prefix
+ command itself, or NULL, if there is no prefix command.
+
This function returns the xmalloc()d name of the new command.
On error a Scheme exception is thrown. */
@@ -469,13 +471,17 @@ char *
gdbscm_parse_command_name (const char *name,
const char *func_name, int arg_pos,
struct cmd_list_element ***base_list,
- struct cmd_list_element **start_list)
+ struct cmd_list_element **start_list,
+ struct cmd_list_element **prefix_cmd)
{
struct cmd_list_element *elt;
int len = strlen (name);
int i, lastchar;
char *msg;
+ if (prefix_cmd != nullptr)
+ *prefix_cmd = nullptr;
+
/* Skip trailing whitespace. */
for (i = len - 1; i >= 0 && (name[i] == ' ' || name[i] == '\t'); --i)
;
@@ -522,6 +528,8 @@ gdbscm_parse_command_name (const char *name,
if (elt->is_prefix ())
{
*base_list = elt->subcommands;
+ if (prefix_cmd != nullptr)
+ *prefix_cmd = elt;
return result.release ();
}
@@ -743,8 +751,9 @@ gdbscm_register_command_x (SCM self)
if (cmdscm_is_valid (c_smob))
scm_misc_error (FUNC_NAME, _("command is already registered"), SCM_EOL);
+ struct cmd_list_element *prefix_cmd = nullptr;
cmd_name = gdbscm_parse_command_name (c_smob->name, FUNC_NAME, SCM_ARG1,
- &cmd_list, &cmdlist);
+ &cmd_list, &cmdlist, &prefix_cmd);
c_smob->cmd_name = gdbscm_gc_xstrdup (cmd_name);
xfree (cmd_name);
@@ -769,11 +778,14 @@ gdbscm_register_command_x (SCM self)
'set prefix' the user will get the help text listing all
of the sub-commands, and for 'show prefix', the user will
see all of the sub-command values. */
- cmd_list_element *first = *cmd_list;
- while (first->prefix != nullptr)
- first = first->prefix;
-
- bool is_show = first->subcommands == &showlist;
+ if (prefix_cmd != nullptr)
+ {
+ while (prefix_cmd->prefix != nullptr)
+ prefix_cmd = prefix_cmd->prefix;
+ }
+
+ bool is_show = (prefix_cmd != nullptr
+ && prefix_cmd->subcommands == &showlist);
if (is_show)
cmd = add_show_prefix_cmd (c_smob->cmd_name,