https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120574
Bug ID: 120574
Summary: Inconsistent array size overflow behavior between -O0
and others optimizations: code compiles at -O1、-O2、O3,
but fails at -O0
Product: gcc
Version: 14.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: 2023091106 at cauc dot edu.cn
Target Milestone: ---
When compiling the following code using GCC with different optimization levels,
-O0 results in a compilation error due to excessive local object size, while
-O1 or other optimizations and above compile and run successfully. This
inconsistency may hide bugs or undefined behavior depending on optimization
flags.
Tested with: gcc (GCC) 12/13/14
========the gcc code========
#include <stdio.h>
void a(void) {
puts("A");
}
void b() {
char arr[(size_t)-1 / 2]; // Test for large array allocation issues
arr[(size_t)-1 / 2]='a';
printf("Array size: %zu\n", sizeof(arr));
}
void c() {
int arr[((size_t)-1)/2 / sizeof(int)]; // Test for integer division and
overflow
arr[((size_t)-1)/2 / sizeof(int)]='a';
printf("Integer array size: %zu\n", sizeof(arr));
}
int main(void)
{
b();
c();
}
========output========
$ gcc-14 -Wall -Wextra -O0 -o test test.c
test.c: 在function ‘b’中:
test.c:7:6: error：total size of local objects 9223372036854775808 exceeds
maximum 9223372036854775296
7 | void b() {
| ^
test.c: in function ‘c’中:
test.c:13:6: error：total size of local objects 9223372036854775808 exceeds
maximum 9223372036854775296
13 | void c() {
| ^
$ gcc-14 -Wall -Wextra -O1 -o test test.c
$ ./test
Array size: 9223372036854775807
Integer array size: 9223372036854775804
========the gcc versions=========
$ gcc-14 -v
Using built-in specs.
COLLECT_GCC=gcc-14
COLLECT_LTO_WRAPPER=/opt/gcc-14/libexec/gcc/x86_64-pc-linux-gnu/14.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --prefix=/opt/gcc-14 --enable-languages=c,c++
--disable-multilib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.1.0 (GCC)
