https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99140
Bug ID: 99140
Summary: missing -Warray-bounds on a negative index into a
multidimensional VLA cast to one-dimensional
Product: gcc
Version: 11.0
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: ---
The negative subscript in the three functions below is diagnosed only when
accessing an ordinary array but not when accessing a VLA.
$ cat t.c && gcc -O2 -S -Wall t.c
void f (void*);
void f_4_8 (int n)
{
int a[4][8];
((int*)a)[-1] = 0; // -Warray-bounds
f (a);
}
void f_4_n (int n)
{
int a[4][n];
((int*)a)[-1] = 0; // missing warning
f (a);
}
void f_n_8 (int n)
{
int a[n][8];
((int*)a)[-1] = 0; // missing warning
f (a);
}
t.c: In function ‘f_4_8’:
t.c:6:12: warning: array subscript -1 is outside array bounds of ‘int[4][8]’
[-Warray-bounds]
6 | ((int*)a)[-1] = 0; // -Warray-bounds
| ~~~~~~~~~^~~~
t.c:5:7: note: while referencing ‘a’
5 | int a[4][8];
| ^
