[RFC] Improve newlib source code compatibility with LLVM clang

[Joel Sherrill]

If [2] is the only patch, it looks mostly safe and straightforward to me at
first glance. Mostly adding a "p" in front of numeric register references,
a lower addition, and a few ifdef's on __clang__ to avoid unsupported
directives. But info documentation is hacked out and there is the addition
of __aarch64_sme_accessible() without explanation.

rdimon-aem.S;208 has a replacement of 1 instruction with 2 with no
explanation.

linux-crt0.c:353 comments out the attribute naked with a C++ comment. I
don't think C++ comments are allowed. If this really needs to disappear, it
likely should just be deleted.

My preference would be a series of patches with specific purposes. For
example, a first patch which adds "p" in front of all the register numbers.
That should eliminate a lot of this patch.

I would like functional additions to be separate from addressing syntax
issues.

Is there anything in there more substantial that I missed?

--joel

On Mon, Jan 20, 2025 at 7:13 AM Volodymyr Turanskyy <
Volodymyr.Turanskyy@arm.com> wrote:

> Hello,
>
>
>
> LLVM Embedded Toolchain for Arm [1] uses newlib as one of libraries for
> embedded development, with a lot of interest from users. Unfortunately,
> newlib cannot be built with LLVM clang out-of-box, because of minor source
> code issues, so the project has to maintain a rather big patch [2] on top
> of newlib.
>
>
>
> Most of the issues are in the assembly syntax, straightforward to fix in a
> way to be supported by both GCC and clang.
>
>
>
> We want to share a series of small patches to update the syntax to improve
> compatibility with both compilers. I will send individual patches to the
> mail list as separate emails for further discussion.
>
>
>
> Note that if there is interest from the newlib community, we would be
> happy to setup a CI that would try to build latest version of newlib to
> show if any new incompatibilities are introduced, however we would not have
> time to fix all of them in timely manner as our focus is on LLVM
> development.
>
>
>
> References:
>
>    1. https://github.com/ARM-software/LLVM-embedded-toolchain-for-Arm
>    2.
>    https://github.com/ARM-software/LLVM-embedded-toolchain-for-Arm/blob/main/patches/newlib/0001-Enable-newlib-build.patch
>
>
>
> Sincerely,
>
>
>
> *Volodymyr Turanskyy* | Principal Software Engineer | CE SW LLVM Team
>
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