linux-kernel - Re: [PATCH 1/3] kbuild: Change CFI_CLANG to depend on __builtin_function

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Date:   Mon, 4 Apr 2022 12:40:46 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        llvm@...ts.linux.dev
Subject: Re: [PATCH 1/3] kbuild: Change CFI_CLANG to depend on __builtin_function_start

On Sat, Apr 2, 2022 at 6:32 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> On Sat, Apr 2, 2022 at 5:19 AM Sami Tolvanen <samitolvanen@...gle.com> wrote:
> >
> > Clang 14 added support for the __builtin_function_start()
> > built-in function, which allows us to implement function_nocfi()
> > without architecture-specific inline assembly. This patch changes
> > CONFIG_CFI_CLANG to depend on the built-in and effectively upgrades
> > the minimum supported compiler version for CFI to Clang 14.
>
> From this description, I think the straight-forward change would be:
>
>     depends on CLANG_VERSION >= 120000
> -->
>     depends on CLANG_VERSION >= 140000
>
> Any reason to avoid this?

I thought testing for the compiler feature was preferred, but I can
certainly just increase the minimum version number here too.

Sami