https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100426
Bug ID: 100426
Summary: missing warning for zero-size VLA
Product: gcc
Version: 11.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
GCC diagnoses calls to most allocation functions with a zero size except for
VLAs. The gimple-ssa-warn-alloca.c pass has code to diagnose zero-size VLAs
but it never triggers because the calls to allocate storage for zero-size VLA
are eliminated.
$ cat z.c && gcc -O2 -S -Wall -Walloca-larger-than=1 -Wvla-larger-than=1
-Walloc-zero z.c
void f (void*);
void f0 (void)
{
f (__builtin_alloca (__builtin_strlen ("")));
}
void f1 (void)
{
f (__builtin_malloc (__builtin_strlen ("")));
}
void f2 (void)
{
extern __attribute__ ((alloc_size (1))) void* allocate (int);
f (allocate (__builtin_strlen ("")));
}
void f3 (void)
{
char a[__builtin_strlen ("")]; // missing warning either here
f (a); // or here
}
z.c: In function ‘f0’:
z.c:5:3: warning: argument to ‘alloca’ is zero [-Walloca-larger-than=]
5 | f (__builtin_alloca (__builtin_strlen ("")));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
z.c: In function ‘f1’:
z.c:10:3: warning: argument 1 value is zero [-Walloc-zero]
10 | f (__builtin_malloc (__builtin_strlen ("")));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
z.c:10:3: note: in a call to built-in allocation function ‘__builtin_malloc’
z.c: In function ‘f2’:
z.c:17:3: warning: argument 1 value is zero [-Walloc-zero]
17 | f (allocate (__builtin_strlen ("")));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
z.c:15:49: note: in a call to allocation function ‘allocate’ declared here
15 | extern __attribute__ ((alloc_size (1))) void* allocate (int);
| ^~~~~~~~
