diff options
| author | Jakub Jelinek <jakub@redhat.com> | 2024-04-20 00:12:36 +0200 |
|---|---|---|
| committer | Jakub Jelinek <jakub@redhat.com> | 2024-04-20 00:12:36 +0200 |
| commit | 2afdecccbaf5c5b1c7a235509b37092540906c02 (patch) | |
| tree | c1d0dff23d1adc5d89b985ffc70bd5919e6dadb7 | |
| parent | a39983bf58d3097c472252f6989d19b60909dd9a (diff) | |
| download | gcc-2afdecccbaf5c5b1c7a235509b37092540906c02.zip gcc-2afdecccbaf5c5b1c7a235509b37092540906c02.tar.gz gcc-2afdecccbaf5c5b1c7a235509b37092540906c02.tar.bz2 | |
c-family: Allow arguments with NULLPTR_TYPE as sentinels [PR114780]
While in C++ the ellipsis argument conversions include
"An argument that has type cv std::nullptr_t is converted to type void*"
in C23 a nullptr_t argument is not promoted in any way, but va_arg
description says:
"the type of the next argument is nullptr_t and type is a pointer type that has the same
representation and alignment requirements as a pointer to a character type."
So, while in C++ check_function_sentinel will never see NULLPTR_TYPE, for
C23 it can see that and currently we incorrectly warn about those.
The only question is whether we should warn on any argument with
nullptr_t type or just about nullptr (nullptr_t argument with integer_zerop
value). Through undefined behavior guess one could pass non-NULL pointer
that way, say by union { void *p; nullptr_t q; } u; u.p = &whatever;
and pass u.q to ..., but valid code should always pass something that will
read as (char *) 0 when read using va_arg (ap, char *), so I think it is
better not to warn rather than warn in those cases.
Note, clang seems to pass (void *)0 rather than expression of nullptr_t
type to ellipsis in C23 mode as if it did the C++ ellipsis argument
conversions, in that case guess not warning about that would be even safer,
but what GCC does I think follows the spec more closely, even when in a
valid program one shouldn't be able to observe the difference.
2024-04-20 Jakub Jelinek <jakub@redhat.com>
PR c/114780
* c-common.cc (check_function_sentinel): Allow as sentinel any
argument of NULLPTR_TYPE.
* gcc.dg/format/sentinel-2.c: New test.
| -rw-r--r-- | gcc/c-family/c-common.cc | 1 | ||||
| -rw-r--r-- | gcc/testsuite/gcc.dg/format/sentinel-2.c | 21 |
2 files changed, 22 insertions, 0 deletions
diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc index 6fa8243..01e3d24 100644 --- a/gcc/c-family/c-common.cc +++ b/gcc/c-family/c-common.cc @@ -5783,6 +5783,7 @@ check_function_sentinel (const_tree fntype, int nargs, tree *argarray) sentinel = fold_for_warn (argarray[nargs - 1 - pos]); if ((!POINTER_TYPE_P (TREE_TYPE (sentinel)) || !integer_zerop (sentinel)) + && TREE_CODE (TREE_TYPE (sentinel)) != NULLPTR_TYPE /* Although __null (in C++) is only an integer we allow it nevertheless, as we are guaranteed that it's exactly as wide as a pointer, and we don't want to force diff --git a/gcc/testsuite/gcc.dg/format/sentinel-2.c b/gcc/testsuite/gcc.dg/format/sentinel-2.c new file mode 100644 index 0000000..4c29f6f --- /dev/null +++ b/gcc/testsuite/gcc.dg/format/sentinel-2.c @@ -0,0 +1,21 @@ +/* PR c/114780 */ +/* { dg-do compile } */ +/* { dg-options "-std=c23 -Wformat" } */ + +#include <stddef.h> + +[[gnu::sentinel]] void foo (int, ...); +[[gnu::sentinel]] void bar (...); + +void +baz (nullptr_t p) +{ + foo (1, 2, nullptr); + foo (3, 4, 5, p); + bar (nullptr); + bar (p); + foo (6, 7, 0); // { dg-warning "missing sentinel in function call" } + bar (0); // { dg-warning "missing sentinel in function call" } + foo (8, 9, NULL); + bar (NULL); +} |