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From:   Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Date:   Tue, 1 Oct 2019 23:06:18 +0200
Message-ID: <CANiq72nZRc5TXxhXSQnMhaeQaP2RuDpHf+1CvC8kDV8_m14WeQ@mail.gmail.com>
Subject: Re: [PATCH] compiler: enable CONFIG_OPTIMIZE_INLINING forcibly
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Nick Desaulniers <ndesaulniers@google.com>,
        Russell King - ARM Linux admin <linux@armlinux.org.uk>,
        Will Deacon <will@kernel.org>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        linux-arch <linux-arch@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Stefan Wahren <wahrenst@gmx.net>,
        Kees Cook <keescook@google.com>,
        clang-built-linux <clang-built-linux@googlegroups.com>
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On Tue, Oct 1, 2019 at 10:53 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> 1. is clearly the most common case, but there is also
>
> 4. Some compiler version (possibly long gone, possibly still current)
> makes bad inlining decisions that result in horrible but functionally
> correct object code for a particular function, and forcing a function to
> be inlined results in what we had expected the compiler to do already.

There is also 5. code that does not even compile without it, e.g.
_static_cpu_has() in x86_64 which requires
__attribute__((always_inline)), at least on GCC 9.2.

For x64_64 it is the only one case I found, though. If you disable
__always_inline everything else compiles and links (in a defconfig).

Cheers,
Miguel