linux-kernel - Re: [PATCH] ctype.h: remove duplicate isdigit() helper

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Message-ID: <CAKwvOdmdv6wABToSpJt5b66E1vD3Ec0QC3DnyZm7f2sJkcsNuw@mail.gmail.com>
Date:   Mon, 26 Oct 2020 11:23:29 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        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 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?

>
> As there is already a compiler builtin, just use that, and make
> it clear we do that by defining a macro.  Unfortunately, clang
> does not have the isdigit() builtin, so this has to be conditional.

TODO(Nick): finish the Clang patch that implements that.
https://reviews.llvm.org/D86508

>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  include/linux/ctype.h | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/ctype.h b/include/linux/ctype.h
> index 363b004426db..c407acb258c2 100644
> --- a/include/linux/ctype.h
> +++ b/include/linux/ctype.h
> @@ -23,10 +23,6 @@ extern const unsigned char _ctype[];
>  #define isalnum(c)     ((__ismask(c)&(_U|_L|_D)) != 0)
>  #define isalpha(c)     ((__ismask(c)&(_U|_L)) != 0)
>  #define iscntrl(c)     ((__ismask(c)&(_C)) != 0)
> -static inline int isdigit(int c)
> -{
> -       return '0' <= c && c <= '9';
> -}
>  #define isgraph(c)     ((__ismask(c)&(_P|_U|_L|_D)) != 0)
>  #define islower(c)     ((__ismask(c)&(_L)) != 0)
>  #define isprint(c)     ((__ismask(c)&(_P|_U|_L|_D|_SP)) != 0)
> @@ -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.

> +#define isdigit(ch) __builtin_isdigit(ch)
> +#endif
> +#endif
> +#ifndef isdigit
> +static inline int isdigit(int c)
> +{
> +       return '0' <= c && c <= '9';
> +}
> +#endif
> +
>  static inline unsigned char __tolower(unsigned char c)
>  {
>         if (isupper(c))
> --
> 2.27.0
>


-- 
Thanks,
~Nick Desaulniers