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

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Date:   Wed, 09 Mar 2022 00:14:06 +0200
From:   Adrian Ratiu <adrian.ratiu@...labora.com>
To:     Daniel Borkmann <daniel@...earbox.net>, 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

Hello Daniel,

On Tue, 08 Mar 2022, Daniel Borkmann <daniel@...earbox.net> wrote:
> 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? 
>

Yes, let's target this for bpf-next. The issue was introduced in 
the 5.17 cycle but indeed it's late. I can do a stable backport to 
5.17 after it releases.

Thanks,
Adrian

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