linux-kernel - Re: [PATCH bpf v2] tools: fix unavoidable GCC call in Clang builds

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Date:   Tue, 8 Mar 2022 18:17:44 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Adrian Ratiu <adrian.ratiu@...labora.com>, netdev@...r.kernel.org
Cc:     llvm@...ts.linux.dev, kernel@...labora.com,
        linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Manoj Gupta <manojgupta@...omium.com>,
        Nathan Chancellor <nathan@...nel.org>, bpf@...r.kernel.org
Subject: Re: [PATCH bpf v2] tools: fix unavoidable GCC call in Clang builds

On 3/8/22 1:14 PM, Adrian Ratiu wrote:
> In ChromeOS and Gentoo we catch any unwanted mixed Clang/LLVM
> and GCC/binutils usage via toolchain wrappers which fail builds.
> This has revealed that GCC is called unconditionally in Clang
> configured builds to populate GCC_TOOLCHAIN_DIR.
> 
> Allow the user to override CLANG_CROSS_FLAGS to avoid the GCC
> call - in our case we set the var directly in the ebuild recipe.
> 
> In theory Clang could be able to autodetect these settings so
> this logic could be removed entirely, but in practice as the
> commit cebdb7374577 ("tools: Help cross-building with clang")
> mentions, this does not always work, so giving distributions
> more control to specify their flags & sysroot is beneficial.
> 
> Suggested-by: Manoj Gupta <manojgupta@...omium.com>
> Suggested-by: Nathan Chancellor <nathan@...nel.org>
> Acked-by: Nathan Chancellor <nathan@...nel.org>
> Signed-off-by: Adrian Ratiu <adrian.ratiu@...labora.com>
> ---
> Changes in v2:
>    * Replaced variable override GCC_TOOLCHAIN_DIR -> CLANG_CROSS_FLAGS

As I understand it from [0] and given we're late in the cycle, this is
targeted for bpf-next not bpf, right?

Thanks,
Daniel

   [0] https://lore.kernel.org/lkml/87czjk4osi.fsf@ryzen9.i-did-not-set--mail-host-address--so-tickle-me/