From 2fb6915fa22dc5524d704afba58a13305dd9f533 Mon Sep 17 00:00:00 2001 From: "H. Peter Anvin" Date: Fri, 18 Jul 2025 11:35:00 -0700 Subject: [PATCH] compiler_types.h: add "auto" as a macro for "__auto_type" "auto" was defined as a keyword back in the K&R days, but as a storage type specifier. No one ever used it, since it was and is the default storage type for local variables. C++11 recycled the keyword to allow a type to be declared based on the type of an initializer. This was finally adopted into standard C in C23. gcc and clang provide the "__auto_type" alias keyword as an extension for pre-C23, however, there is no reason to pollute the bulk of the source base with this temporary keyword; instead define "auto" as a macro unless the compiler is running in C23+ mode. This macro is added in because that header is included in some of the tools headers, wheres is not as it has a bunch of very kernel-specific things in it. [ Cc: stable to reduce potential backporting burden. ] Signed-off-by: H. Peter Anvin (Intel) Acked-by: Miguel Ojeda Cc: --- include/linux/compiler_types.h | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 3eac51d684261..41172a28ce76d 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -13,6 +13,19 @@ #ifndef __ASSEMBLY__ +/* + * C23 introduces "auto" as a standard way to define type-inferred + * variables, but "auto" has been a (useless) keyword even since K&R C, + * so it has always been "namespace reserved." + * + * Until at some future time we require C23 support, we need the gcc + * extension __auto_type, but there is no reason to put that elsewhere + * in the source code. + */ +#if __STDC_VERSION__ < 202311L +# define auto __auto_type +#endif + /* * Skipped when running bindgen due to a libclang issue; * see https://github.com/rust-lang/rust-bindgen/issues/2244. -- 2.47.3