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Date: Mon, 26 Oct 2020 20:22:09 +0100 From: Arnd Bergmann <arnd@...nel.org> To: Nick Desaulniers <ndesaulniers@...gle.com> Cc: Nathan Chancellor <natechancellor@...il.com>, LKML <linux-kernel@...r.kernel.org>, clang-built-linux <clang-built-linux@...glegroups.com>, Miguel Ojeda <miguel.ojeda.sandonis@...il.com> Subject: Re: [PATCH] ctype.h: remove duplicate isdigit() helper On Mon, Oct 26, 2020 at 7:23 PM 'Nick Desaulniers' via Clang Built Linux <clang-built-linux@...glegroups.com> wrote: > > On Mon, Oct 26, 2020 at 9:23 AM Arnd Bergmann <arnd@...nel.org> wrote: > > > > From: Arnd Bergmann <arnd@...db.de> > > > > gcc warns a few thousand times about the isdigit() shadow: > > > > include/linux/ctype.h:26:19: warning: declaration of 'isdigit' shadows a built-in function [-Wshadow] > > Don't all functions defined here shadow builtins in GCC? Why is > `isdigit` unique? Is that because it's a `static inline` definition > vs a function like macro? If that's the case, what's the harm in > converting it to a function like macro if that silences the warning? It was originally a macro but got changed to an inline function in 1204c77f9b6a ("include/linux/ctype.h: make isdigit() table lookupless"), apparently in order to avoid evaluating the argument more than once. I suppose we could make it a statement expression with a local variable like #define isdigit(c) ({ __auto_type __c = (c); '0' <= __c && __c <= '9'; }) > > @@ -39,6 +35,18 @@ static inline int isdigit(int c) > > #define isascii(c) (((unsigned char)(c))<=0x7f) > > #define toascii(c) (((unsigned char)(c))&0x7f) > > > > +#if defined __has_builtin > > #ifdef > > only use `defined` explicitly when there's more than one condition > being checked with logical `&&` or `||`. > > > +#if __has_builtin(__builtin_isdigit) > > GCC only recently gained the `__has_builtin` macro (I filed the bug); > I would like to see something akin to > include/linux/compiler_attributes.h but using `__has_builtin` like > compiler_attributes.h uses `__has_attribute`. That way we avoid > spaghetti like this throughout the kernel. Ok. I've added a 'has_builtin()' macro (without underscores) in linux/compiler.h in version 2. I don't use it anywhere else in my current series, so there should be no dependencies. Arnd
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