[1/4] gdb: fix printf of wchar_t early in a gdb session
Commit Message
Given this test program:
#include <wchar.h>
const wchar_t wide_str[] = L"wide string";
int
main (void)
{
return 0;
}
I observed this GDB behaviour:
$ gdb -q /tmp/printf-wchar_t
Reading symbols from /tmp/printf-wchar_t...
(gdb) start
Temporary breakpoint 1 at 0x40110a: file /tmp/printf-wchar_t.c, line 8.
Starting program: /tmp/printf-wchar_t
Temporary breakpoint 1, main () at /tmp/printf-wchar_t.c:8
25 return 0;
(gdb) printf "%ls\n", wide_str
(gdb)
Notice that the printf results in a blank line rather than the
expected 'wide string' output.
I tracked the problem down to printf_wide_c_string (in printcmd.c), in
this function we do this:
struct type *wctype = lookup_typename (current_language,
"wchar_t", NULL, 0);
int wcwidth = wctype->length ();
the problem here is that 'wchar_t' is a typedef. If we look at the
comment on type::length() we see this:
/* Note that if thistype is a TYPEDEF type, you have to call check_typedef.
But check_typedef does set the TYPE_LENGTH of the TYPEDEF type,
so you only have to call check_typedef once. Since value::allocate
calls check_typedef, X->type ()->length () is safe. */
What this means is that after calling lookup_typename we should call
check_typedef in order to ensure that the length of the typedef has
been setup correctly. We are not doing this in printf_wide_c_string,
and so wcwidth is incorrectly calculated as 0. This is what leads GDB
to print an empty string.
We can see in c_string_operation::evaluate (in c-lang.c) an example of
calling check_typedef specifically to fix this exact issue.
Initially I did fix this problem by adding a check_typedef call into
printf_wide_c_string, but then I figured why not move the
check_typedef call up into lookup_typename itself, that feels like it
should be harmless when looking up a non-typedef type, but will avoid
bugs like this when looking up a typedef. So that's what I did.
I can then remove the extra check_typedef call from c-lang.c, I don't
see any other places where we had extra check_typedef calls. This
doesn't mean we definitely had bugs -- so long as we never checked the
length, or, if we knew that check_typedef had already been called,
then we would be fine.
I don't see any test regressions after this change, and my new test
case is now passing.
---
gdb/c-lang.c | 3 ---
gdb/gdbtypes.c | 11 ++++++----
gdb/gdbtypes.h | 14 ++++++++++--
gdb/testsuite/gdb.base/printf-wchar_t.c | 26 +++++++++++++++++++++++
gdb/testsuite/gdb.base/printf-wchar_t.exp | 26 +++++++++++++++++++++++
5 files changed, 71 insertions(+), 9 deletions(-)
create mode 100644 gdb/testsuite/gdb.base/printf-wchar_t.c
create mode 100644 gdb/testsuite/gdb.base/printf-wchar_t.exp
Comments
>>>>> Andrew Burgess via Gdb-patches <gdb-patches@sourceware.org> writes:
> Initially I did fix this problem by adding a check_typedef call into
> printf_wide_c_string, but then I figured why not move the
> check_typedef call up into lookup_typename itself, that feels like it
> should be harmless when looking up a non-typedef type, but will avoid
> bugs like this when looking up a typedef. So that's what I did.
Makes sense to me.
It's pretty typical for a missing check_typedef to wind up being a bug
in some scenario. I think one of the dreams for method-izing struct
type is to make this impossible -- like having the various methods call
check_typedef themselves (if needed) before returning an answer.
Anyway, this looks good to me.
Reviewed-By: Tom Tromey <tom@tromey.com>
Tom
@@ -615,9 +615,6 @@ c_string_operation::evaluate (struct type *expect_type,
internal_error (_("unhandled c_string_type"));
}
- /* Ensure TYPE_LENGTH is valid for TYPE. */
- check_typedef (type);
-
/* If the caller expects an array of some integral type,
satisfy them. If something odder is expected, rely on the
caller to cast. */
@@ -1648,9 +1648,7 @@ type_name_or_error (struct type *type)
objfile ? objfile_name (objfile) : "<arch>");
}
-/* Lookup a typedef or primitive type named NAME, visible in lexical
- block BLOCK. If NOERR is nonzero, return zero if NAME is not
- suitably defined. */
+/* See gdbtypes.h. */
struct type *
lookup_typename (const struct language_defn *language,
@@ -1662,7 +1660,12 @@ lookup_typename (const struct language_defn *language,
sym = lookup_symbol_in_language (name, block, VAR_DOMAIN,
language->la_language, NULL).symbol;
if (sym != NULL && sym->aclass () == LOC_TYPEDEF)
- return sym->type ();
+ {
+ struct type *type = sym->type ();
+ /* Ensure the length of TYPE is valid. */
+ check_typedef (type);
+ return type;
+ }
if (noerr)
return NULL;
@@ -2586,8 +2586,18 @@ extern void check_stub_method_group (struct type *, int);
extern char *gdb_mangle_name (struct type *, int, int);
-extern struct type *lookup_typename (const struct language_defn *,
- const char *, const struct block *, int);
+/* Lookup a typedef or primitive type named NAME, visible in lexical block
+ BLOCK. If NOERR is nonzero, return zero if NAME is not suitably
+ defined.
+
+ If this function finds a suitable type then check_typedef is called on
+ the type, this ensures that if the type being returned is a typedef
+ then the length of the type will be correct. The original typedef will
+ still be returned, not the result of calling check_typedef. */
+
+extern struct type *lookup_typename (const struct language_defn *language,
+ const char *name,
+ const struct block *block, int noerr);
extern struct type *lookup_template_type (const char *, struct type *,
const struct block *);
new file mode 100644
@@ -0,0 +1,26 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2023 Free Software Foundation, Inc.
+
+ 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/>. */
+
+#include <wchar.h>
+
+const wchar_t wide_str[] = L"wide string";
+
+int
+main (void)
+{
+ return 0;
+}
new file mode 100644
@@ -0,0 +1,26 @@
+# Copyright 2023 Free Software Foundation, Inc.
+
+# 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/>.
+
+standard_testfile
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile]} {
+ return -1
+}
+
+if {![runto_main]} {
+ return -1
+}
+
+gdb_test {printf "%ls\n", wide_str} "^wide string"