https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103858
Bug ID: 103858
Summary: [12 Regression] strlen() implementation is optimized
into a call to strlen() at -O2, causing infinite
recursion
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: dani at danielbertalan dot dev
Target Milestone: ---
Compiler Explorer link: https://godbolt.org/z/h419G55P4
The following function is folded into a call to strlen() by gcc 12 (commit
61e53698a08dc1d9a54d785218af687a6751c1b3) at -O2, unless -fno-builtin-strlen is
specified. This function is taken from a (naive) libc implementation, where
this is the only definition of strlen(), so it ends up calling itself
recursively, overflowing the stack.
#include <stddef.h>
size_t strlen(const char* str)
{
size_t len = 0;
while (*(str++))
++len;
return len;
}
x86_64 assembly output:
strlen:
cmp BYTE PTR [rdi], 0
je .L3
lea rax, [rdi+1]
sub rsp, 8
mov rdi, rax
call strlen
add rsp, 8
add rax, 1
ret
.L3:
xor eax, eax
ret
My workaround is to compile our libc with -ffreestanding/-fno-builtin, but I'd
like to avoid that, as it might prevent other (valid) optimizations from being
performed on our code.
