https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102953
--- Comment #17 from Andrew Cooper <andrew.cooper3 at citrix dot com> ---
I think I've found a bug in the -fcf-check-attribute implementation.
$ cat fnptr-array-arg.c
static int __attribute__((cf_check)) foo(char a[], int b)
{
return 0;
}
int (*ptr)(char[], int) = foo;
$ gcc -Wall -fcf-protection=branch -mmanual-endbr -fcf-check-attribute=no -c
fnptr-array-arg.c -o tmp.o && objdump -d tmp.o
fnptr-array-arg.c:5:27: warning: initialization of 'int (*)(char *, int)'
from incompatible pointer type 'int (__attribute__((nocf_check)) *)(char *,
int)' [-Wincompatible-pointer-types]
5 | int (*ptr)(char[], int) = foo;
| ^~~
tmp.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <foo>:
0: 31 c0 xor %eax,%eax
2: c3 retq
Despite the explicit cf_check, a diagnostic is raised complaining about
cf_check-ness of the pointer, and the generated code has no `endbr64`
instruction.
This issue only manifests when using array arguments in the function. When
switching `char[]` for `char*`, everything works as expected. Also, dropping
-fcf-check-attribute=no also causes things to work.
$ gcc -Wall -fcf-protection=branch -mmanual-endbr -c fnptr-array-arg.c -o
tmp.o && objdump -d tmp.o
tmp.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <foo>:
0: f3 0f 1e fa endbr64
4: 31 c0 xor %eax,%eax
6: c3 retq
Something about the array type seems to cause the explicit cf_check attribute
to be lost.
