[Buildroot] Status of LLVM

Romain Naour romain.naour at gmail.com
Wed Aug 5 15:55:24 UTC 2020

Hello Thomas,

Le 05/08/2020 à 17:31, Thomas Petazzoni a écrit :
> On Wed, 5 Aug 2020 16:36:12 +0200
> Romain Naour <romain.naour at gmail.com> wrote:
>> Last year I was able to build an aarch64 system with clang 8 (rootfs + kernel)
>> on a Potato Board.
>> Recently I tried again with a riscv64 target running under qemu:
>> https://asciinema.org/a/DDspJVktlVl1Rh97dwLgtYcRY
>> Clang: 10.0
>> kernel: 5.7.12
>> Busybox: 1.31.1 + patch
>> gcc toolchain: Bootlin riscv64--glibc--bleeding-edge-2020.02-2.defconfig
>> I need some time to continue to work on this series and convince upstream to add
>> cland support in Buildroot. But it means more maintenance work for Buildroot
>> maintainers/contributors to fix all packages that fail to build with clang.
>> At least, we need to enable autobuilders testing with clang if this support is
>> added.
> I think it makes sense to have support for clang in Buildroot, and we
> can certainly add testing for clang configurations in our autobuilders.
> The one thing that was still a bit unclear for me is whether it is
> possible to build a system with just clang, without a gcc compiler at
> all. Indeed, Buildroot isn't really suited/designed for building two
> different compilers/toolchains.

>From my testing, we can build the kernel on x86, Aarch64 and riscv64 if we use a
recent enough version (5.7 for riscv64 only with clang 10).

We need the gcc toolchain to provide the libc and other object files
(crtbegin.o) not provided by LLVM/Clang. But the series replace GCC compiler by
clang in the package infrastructure, so we can even remove gcc from host
directory (I tested).

We don't need to build a toolchain with Buildroot, we can use an external
toolchain (I used the Bootlin riscv64 prebuilt toolchain).

For now, we are building host-llvm and host-clang for each build.
It would be interesting to allow an external prebuilt Clang toolchain.

About bootloaders, I didn't test to build them with clang.
Maybe for some packages, we still need a gcc compiler.

Best regards,

> Thomas

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