linux-kernel - Re: odd endianness toolchains for crosstool

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Message-Id: <2582a7d1-11bd-4952-a2e2-ab3f6b816f0c@app.fastmail.com>
Date: Tue, 03 Sep 2024 06:59:49 +0000
From: "Arnd Bergmann" <arnd@...db.de>
To: "Nathan Chancellor" <nathan@...nel.org>
Cc: "Jason A . Donenfeld" <Jason@...c4.com>, linux-kernel@...r.kernel.org
Subject: Re: odd endianness toolchains for crosstool

On Tue, Sep 3, 2024, at 01:23, Nathan Chancellor wrote:
> On Thu, Aug 29, 2024 at 10:25:32PM +0200, Arnd Bergmann wrote:
>> On Thu, Aug 29, 2024, at 17:51, Jason A. Donenfeld wrote:
>> 
>> I wonder if the ones you list as missing all work with Nathan's clang
>> builds from https://mirrors.edge.kernel.org/pub/tools/llvm/ instead.
>> 
>> As far as I can tell, the main missing bit here is libgcc, which
>> is not always built along with gcc for all possible targets.
>> The llvm replacement for libgcc is https://compiler-rt.llvm.org/,
>> and you may have to build that in addition to musl when you try it.
>> 
>> I don't know if compiler-rt also works with gcc, but if it does,
>> that should fix most of the ones that you report as failing above.
>> The only one that won't work at all is um because the x86 toolchain
>> is already unable to build a kernel for that.
>
> I doubt my toolchains would fix this issue. As far as I am aware, only
> the native compiler runtime is included, not any of the cross ones, as
> the kernel itself does not use them. However, I suspect it would not be
> too difficult to cross build compiler-rt standalone and stitch it into
> my builds separately if desired.

Right, that's what I meant: building compiler-rt for all the
supported targets on clang should not be that hard, it would be
just another step on top of building musl. Doing the same for
gcc may be a different story as libgcc is not usually built as
a standalone library and compiler-rt may require building with
clang rather than gcc.

> FWIW, I have used your toolchains to build UML but maybe that is
> environment dependent?

Did you do that on x86? I only tried on arm64, where it is built
as a nolibc toolchain. Cross-building native x86 toolchains on arm64
is always tricky and I had expected that this would also be
a nolibc version, but it's possible that I accidentally built it
against the x86 glibc as well.

      Arnd