linux-kernel - Re: [PATCH v2 1/2] sparc,x86: vdso: remove meaningless undefining CONFIG_OPTIMIZE

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Date:   Thu, 20 Feb 2020 10:41:55 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        clang-built-linux@...glegroups.com,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        sparclinux@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        "David S. Miller" <davem@...emloft.net>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] sparc,x86: vdso: remove meaningless undefining
 CONFIG_OPTIMIZE_INLINING

On Thu, Feb 20, 2020 at 08:08:06PM +0900, Masahiro Yamada wrote:
> The code, #undef CONFIG_OPTIMIZE_INLINING, is not working as expected
> because <linux/compiler_types.h> is parsed before vclock_gettime.c
> since 28128c61e08e ("kconfig.h: Include compiler types to avoid missed
> struct attributes").
> 
> Since then, <linux/compiler_types.h> is included really early by
> using the '-include' option. So, you cannot negate the decision of
> <linux/compiler_types.h> in this way.
> 
> You can confirm it by checking the pre-processed code, like this:
> 
>   $ make arch/x86/entry/vdso/vdso32/vclock_gettime.i
> 
> There is no difference with/without CONFIG_CC_OPTIMIZE_FOR_SIZE.
> 
> It is about two years since 28128c61e08e. Nobody has reported a
> problem (or, nobody has even noticed the fact that this code is not
> working).
> 
> It is ugly and unreliable to attempt to undefine a CONFIG option from
> C files, and anyway the inlining heuristic is up to the compiler.
> 
> Just remove the broken code.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> Acked-by: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>

Reviewed-by: Nathan Chancellor <natechancellor@...il.com>