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From:   Adrian Ratiu <adrian.ratiu@collabora.com>
To:     Daniel Borkmann <daniel@iogearbox.net>, netdev@vger.kernel.org
Cc:     llvm@lists.linux.dev, kernel@collabora.com,
        linux-kernel@vger.kernel.org,
        Nick Desaulniers <ndesaulniers@google.com>,
        Manoj Gupta <manojgupta@chromium.com>,
        Nathan Chancellor <nathan@kernel.org>, bpf@vger.kernel.org
Subject: Re: [PATCH bpf v2] tools: fix unavoidable GCC call in Clang builds
In-Reply-To: <6e82ffbb-ebc8-30e8-2326-95712578ee07@iogearbox.net>
References: <20220308121428.81735-1-adrian.ratiu@collabora.com>
 <6e82ffbb-ebc8-30e8-2326-95712578ee07@iogearbox.net>
Date:   Wed, 09 Mar 2022 00:14:06 +0200
Message-ID: <87fsnsrt1t.fsf@ryzen9.i-did-not-set--mail-host-address--so-tickle-me>
MIME-Version: 1.0
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Hello Daniel,

On Tue, 08 Mar 2022, Daniel Borkmann <daniel@iogearbox.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@chromium.com> Suggested-by: Nathan Chancellor 
>> <nathan@kernel.org> Acked-by: Nathan Chancellor 
>> <nathan@kernel.org> Signed-off-by: Adrian Ratiu 
>> <adrian.ratiu@collabora.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/