https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108796
Bug ID: 108796 Summary: GCC 13 accepts [[noreturn]] attribute without -std=c2x Product: gcc Version: 13.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: sam at gentoo dot org Target Milestone: --- Created attachment 54462 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54462&action=edit foo.i GCC 13 (13.0.1 20230212) seems to accept [[noreturn]] as an attribute even when not in C2x mode. This leads to a build failure with sudo-1.9.13 (https://github.com/sudo-project/sudo/issues/239) since https://github.com/sudo-project/sudo/commit/e707ffe58b3ccfe5c72f54c38eac1d7069d5021e. Clang 16.0.0_rc2 does not accept it unless passing -std=c2x. Is this intentional or not? Thanks. foo.c: ``` #include <stdlib.h> [[noreturn]] void foo(void) { abort(); } int main() { foo(); } ``` ``` $ gcc-13 --version gcc-13 (Gentoo Hardened 13.0.1_pre20230212 p8) 13.0.1 20230212 (experimental) Copyright (C) 2023 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. $ gcc-13 -std=c2x -O2 /tmp/foo.c # fine $ gcc-13 -std=c99 -O2 /tmp/foo.c # fine $ gcc-13 -O2 /tmp/foo.c -o /tmp/foo # fine $ clang-16 --version clang version 16.0.0 # actually 16.0.0_rc2 Target: x86_64-pc-linux-gnu Thread model: posix InstalledDir: /usr/lib/llvm/16/bin Configuration file: /etc/clang/clang.cfg $ clang-16 -O2 /tmp/foo.c -o /tmp/foo /tmp/foo.c:3:2: error: expected expression [[noreturn]] void foo(void) { ^ /tmp/foo.c:3:14: error: expected identifier or '(' [[noreturn]] void foo(void) { ^ /tmp/foo.c:8:2: error: call to undeclared function 'foo'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration] foo(); ^ 3 errors generated. $ clang-16 -std=c2x -O2 /tmp/foo.c -o /tmp/foo # fine ```