https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106699
Bug ID: 106699
Summary: Since gcc 12, deferencing constant literal addresses
triggers -Warray-bounds warning
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: yann at droneaud dot fr
Target Milestone: ---
Since GCC 12.1, compiling memtest86+ triggers the following warning:
In function 'find_rsdp',
inlined from 'acpi_init' at ../system/acpi.c:329:29:
../system/acpi.c:185:29: warning: array subscript 0 is outside array bounds of
'uint16_t[0]' {aka 'short unsigned int[]'} [-Warray-bounds]
185 | uintptr_t address = *(uint16_t *)0x40E << 4;
| ^~~~~~~~~~~~~~~~~~
../system/hwctrl.c: In function 'reboot':
../system/hwctrl.c:76:9: warning: array subscript 0 is outside array bounds of
'uint16_t[0]' {aka 'short unsigned int[]'} [-Warray-bounds]
76 | *((uint16_t *)0x472) = 0x1234;
| ^~~~~~~~~~~~~~~~~~~~
In function 'find_cpus_in_floating_mp_struct',
inlined from 'smp_init' at ../system/smp.c:543:39:
../system/smp.c:346:29: warning: array subscript 0 is outside array bounds of
'uint16_t[0]' {aka 'short unsigned int[]'} [-Warray-bounds]
346 | uintptr_t address = *(uint16_t *)0x40E << 4;
| ^~~~~~~~~~~~~~~~~~
Sure using integer literal as a pointer is a recipe for disaster in most cases.
But it's for a freestanding environment, a bootloader, a kernel.
So -Warray-bounds should not infer an address points to a empty array.
A minimal test case:
#include <stdint.h>
void write(void) {
*((uint16_t *)0x472) = 0x1234;
}
uint16_t read(void) {
return *(uint16_t *)0x40E << 4;
}
https://godbolt.org/z/c9993xx41
