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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Fri, 28 Jan 2022 14:49:15 -0800
Message-ID: <CAKwvOd=Ab+GWNzSC6eaDWTVDF6gJQ9fDDMT3hep-DzhrEA6DpQ@mail.gmail.com>
Subject: Re: [PATCH v2] kbuild: Add environment variables for userprogs flags
To:     Elliot Berman <quic_eberman@quicinc.com>
Cc:     Masahiro Yamada <masahiroy@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Nathan Chancellor <nathan@kernel.org>,
        Matthias Maennich <maennich@google.com>,
        linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev, Fangrui Song <maskray@google.com>
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 On Fri, Jan 28, 2022 at 2:45 PM Fangrui Song <maskray@google.com> wrote:
>
> On 2022-01-28, Elliot Berman wrote:
> >Allow additional arguments be passed to userprogs compilation.
> >Reproducible clang builds need to provide a sysroot and gcc path to
> >ensure same toolchain is used across hosts. KCFLAGS is not currently
> >used for any user programs compilation, so add new USERCFLAGS and
> >USERLDFLAGS which serves similar purpose as HOSTCFLAGS/HOSTLDFLAGS.
> >
> >Specifically, I'm trying to force CC_CAN_LINK to consistently fail in
> >an environment where a user sysroot is not specifically available.
> >Currently, Clang might automatically detect GCC installation on hosts
> >which have it installed to a default location in /. With addition of
> >these environment variables, you can specify flags such as:
> >
> >$ make USERCFLAGS=--sysroot=/dev/null USERLDFLAGS=-Wl,--sysroot=/dev/null
> >
> >to force sysroot detection to fail.
>
> -Wl,--sysroot=/dev/null => --sysroot
>
> As I mentioned in
> https://lore.kernel.org/all/20220128031549.w5a4bilxbkppagfu@google.com/
> -Wl,--sysroot=/dev/null does not suppress search paths like -L/lib .

In that case, Elliot, can you please test whether USERLDFLAGS is
necessary to be specified AT ALL? Maybe we can drop that addition from
this patch if so?
-- 
Thanks,
~Nick Desaulniers