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Date:   Fri, 18 Oct 2019 15:02:10 -0500
From:   Segher Boessenkool <segher@kernel.crashing.org>
To:     Nathan Chancellor <natechancellor@gmail.com>
Cc:     Nick Desaulniers <ndesaulniers@google.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 3/3] powerpc/prom_init: Use -ffreestanding to avoid a reference to bcmp
Message-ID: <20191018200210.GR28442@gate.crashing.org>
References: <20190911182049.77853-1-natechancellor@gmail.com> <20191014025101.18567-1-natechancellor@gmail.com> <20191014025101.18567-4-natechancellor@gmail.com> <20191014093501.GE28442@gate.crashing.org> <CAKwvOdmcUT2A9FG0JD9jd0s=gAavRc_h+RLG6O3mBz4P1FfF8w@mail.gmail.com> <20191014191141.GK28442@gate.crashing.org> <20191018190022.GA1292@ubuntu-m2-xlarge-x86>
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On Fri, Oct 18, 2019 at 12:00:22PM -0700, Nathan Chancellor wrote:
> Just as an FYI, there was some more discussion around the availablity
> and use of bcmp in this LLVM bug which spawned
> commit 5f074f3e192f ("lib/string.c: implement a basic bcmp").
> 
> https://bugs.llvm.org/show_bug.cgi?id=41035#c13
> 
> I believe this is the proper solution but I am fine with whatever works,
> I just want our CI to be green without any out of tree patches again...

I think the proper solution is for the kernel to *do* use -ffreestanding,
and then somehow tell the kernel that memcpy etc. are the standard
functions.  A freestanding GCC already requires memcpy, memmove, memset,
memcmp, and sometimes abort to exist and do the standard thing; why cannot
programs then also rely on it to be the standard functions.

What exact functions are the reason the kernel does not use -ffreestanding?
Is it just memcpy?  Is more wanted?


Segher