https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98217
Martin Sebor <msebor at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Severity|normal |enhancement
CC| |msebor at gcc dot gnu.org
Keywords| |diagnostic
Status|UNCONFIRMED |WAITING
Last reconfirmed| |2020-12-09
--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
-Wvla-larger-than=<byte-size> seems close to the feature you're looking for:
$ cat pr98217.c && gcc -O2 -S -Wvla-larger-than=0 pr98217.c
void f (void*, ...);
void func1(int n, int array[n]) /* ok, no warning */
{
int array2[n]; /* bad, VLA on stack, warn! */
int (*array3)[n]; /* ok, no VLA on stack, so no warning */
f (array, array2, array3);
}
pr98217.c: In function ‘func1’:
pr98217.c:5:7: warning: argument to variable-length array may be too large
[-Wvla-larger-than=]
5 | int array2[n]; /* bad, VLA on stack, warn! */
| ^~~~~~
The warning triggers whenever a VLA is either a) known to be larger than the
limit or b) not known to be less than or equal to it. Please let us know if
this isn't sufficient.
For better portability, the solution to the VLA bound parameter problem I would
recommend for single-dimensional VLAs over the forward parameter declaration is
attribute access:
$ cat pr98217-2.c && gcc -S pr98217-2.c
typedef __SIZE_TYPE__ size_t;
__attribute__ ((access (read_write, 1, 2)))
void my_memset (char *p, size_t n, char v)
{
__builtin_memset (p, v, n);
}
char a[3];
void f (void)
{
my_memset (a, 3 * sizeof a, 0);
}
pr98217-2.c: In function ‘f’:
pr98217-2.c:13:3: warning: ‘my_memset’ accessing 9 bytes in a region of size 3
[-Wstringop-overflow=]
13 | my_memset (a, 3 * sizeof a, 0);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
pr98217-2.c:4:6: note: in a call to function ‘my_memset’ declared with
attribute ‘access (read_write, 1, 2)’
4 | void my_memset (char p[], size_t n, char v)
| ^~~~~~~~~
(Worth noting is that neither works reliably when the function is inlined and
the association between the array and its bound is lost.)
