https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116605
Bug ID: 116605
Summary: __builtin_object_size and
__builtin_dynamic_object_size in mode 1 fall back to
mode 0 for rows of multidimensional arrays
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: gustavo at embeddedor dot com
Target Milestone: ---
__builtin_object_size() and __builtin_dynamic_object_size() in mode 1 fail to
correctly determine the size of multidimensional arrays when the addresses of
their rows are passed as arguments. In this scenario, the built-in functions
fall back to mode 0. See the example code below[1].
#include <stdio.h>
#define expect(p, _v) do { \
size_t v = _v; \
if (p == v) \
printf("ok: %s == %zu\n", #p, p); \
else \
printf("WAT: %s == %zu (expected %zu)\n", #p, p, v); \
} while (0);
const char array[][10] =
{
[0] = "0123456789",
[1] = "0123456789",
[2] = "0123456789",
[3] = "0123456789",
[4] = "0123456789"
};
int main(void) {
/* the whole object: array */
printf("\nWhole object: sizeof(array) = %zu\n", sizeof(array));
expect(sizeof(array), 50);
expect(__builtin_object_size(array, 1), 50);
expect(__builtin_object_size(array, 0), 50);
expect(__builtin_dynamic_object_size(array, 1), 50);
expect(__builtin_dynamic_object_size(array, 0), 50);
/* first row: *array */
printf("\nFirst row: sizeof(*array) = %zu\n", sizeof(*array));
expect(sizeof(*array), 10);
expect(__builtin_object_size(*array, 1), 10);
expect(__builtin_object_size(*array, 0), 50);
expect(__builtin_dynamic_object_size(*array, 1), 10);
expect(__builtin_dynamic_object_size(*array, 0), 50);
/* second row: array[1] */
printf("\nSecond row: sizeof(array[1]) = %zu\n", sizeof(array[1]));
expect(sizeof(array[1]), 10);
expect(__builtin_object_size(array[1], 1), 10);
expect(__builtin_object_size(array[1], 0), 40);
expect(__builtin_dynamic_object_size(array[1], 1), 10);
expect(__builtin_dynamic_object_size(array[1], 0), 40);
return 0;
}
Clang (trunk) correctly resolves the sizes:
Whole object: sizeof(array) = 50
ok: sizeof(array) == 50
ok: __builtin_object_size(array, 1) == 50
ok: __builtin_object_size(array, 0) == 50
ok: __builtin_dynamic_object_size(array, 1) == 50
ok: __builtin_dynamic_object_size(array, 0) == 50
First row: sizeof(*array) = 10
ok: sizeof(*array) == 10
ok: __builtin_object_size(*array, 1) == 10
ok: __builtin_object_size(*array, 0) == 50
ok: __builtin_dynamic_object_size(*array, 1) == 10
ok: __builtin_dynamic_object_size(*array, 0) == 50
Second row: sizeof(array[1]) = 10
ok: sizeof(array[1]) == 10
ok: __builtin_object_size(array[1], 1) == 10
ok: __builtin_object_size(array[1], 0) == 40
ok: __builtin_dynamic_object_size(array[1], 1) == 10
ok: __builtin_dynamic_object_size(array[1], 0) == 40
However, GCC (trunk) produces some incorrect results:
Whole object: sizeof(array) = 50
ok: sizeof(array) == 50
ok: __builtin_object_size(array, 1) == 50
ok: __builtin_object_size(array, 0) == 50
ok: __builtin_dynamic_object_size(array, 1) == 50
ok: __builtin_dynamic_object_size(array, 0) == 50
First row: sizeof(*array) = 10
ok: sizeof(*array) == 10
WAT: __builtin_object_size(*array, 1) == 50 (expected 10)
ok: __builtin_object_size(*array, 0) == 50
WAT: __builtin_dynamic_object_size(*array, 1) == 50 (expected 10)
ok: __builtin_dynamic_object_size(*array, 0) == 50
Second row: sizeof(array[1]) = 10
ok: sizeof(array[1]) == 10
WAT: __builtin_object_size(array[1], 1) == 40 (expected 10)
ok: __builtin_object_size(array[1], 0) == 40
WAT: __builtin_dynamic_object_size(array[1], 1) == 40 (expected 10)
ok: __builtin_dynamic_object_size(array[1], 0) == 40
[1] https://godbolt.org/z/afWMKKoGo
