From: Kees Cook <keescook@chromium.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org, linux@armlinux.org.uk,
arnd@arndb.de, ndesaulniers@google.com, nathan@kernel.org
Subject: Re: [PATCH] ARM: Thumb2: avoid __builtin_thread_pointer() on Clang
Date: Thu, 28 Oct 2021 09:52:30 -0700 [thread overview]
Message-ID: <202110280952.352F66D8@keescook> (raw)
In-Reply-To: <20211028083527.1057158-1-ardb@kernel.org>
On Thu, Oct 28, 2021 at 10:35:27AM +0200, Ard Biesheuvel wrote:
> If available, we use the __builtin_thread_pointer() helper to get the
> value of the TLS register, to help the compiler understand that it
> doesn't need to reload it every time we access 'current'.
>
> Unfortunately, Clang fails to emit the MRC system register read
> directly when building for Thumb2, and instead, it issues a call to the
> __aeabi_read_tp helper, which the kernel does not provide, and so this
> result in link failures at build time.
>
> So create a special case for this, and emit the MRC directly using an
> asm() block, just like we do when the helper is not available to begin
> with.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1485
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
--
Kees Cook
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prev parent reply other threads:[~2021-10-28 16:53 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-28 8:35 [PATCH] ARM: Thumb2: avoid __builtin_thread_pointer() on Clang Ard Biesheuvel
2021-10-28 16:25 ` Nick Desaulniers
2021-10-28 16:32 ` Nathan Chancellor
2021-10-28 16:52 ` Kees Cook [this message]
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