[llvm-dev] A libc in LLVM

Jake Ehrlich via llvm-dev
Mon, 24 Jun 2019 22:37:38 -0000

disclaimer: I work at Google so don't take my +1 as an independent vote
forward.

We would like to use this on Fuchsia and I am particularly interested in
creating a dynamic linking library for ELF with Roland McGrath's guidance.
We spoke about creating a library for writing dynamic linkers internally
and I don't see why this can't be upstreamed.

On Fuchsia we critically need support for AArch64; What do you expect to be
architecture dependent? I struggled to think of where the architecture and
not the operating system was the issue.

On Mon, Jun 24, 2019 at 3:23 PM Siva Chandra via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hello LLVM Developers,
>
> Within Google, we have a growing range of needs that existing libc
> implementations don't quite address. This is pushing us to start
working on
> a new libc implementation.
>
> Informal conversations with others within the LLVM community has told us
> that a libc in LLVM is actually a broader need, and we are increasingly
> consolidating our toolchains around LLVM. Hence, we wanted to see if the
> LLVM project would be interested in us developing this upstream as part of
> the project.
>
> To be very clear: we don't expect our needs to exactly match everyone
> else's -- part of our impetus is to simplify things wherever we can,
and
> that may not quite match what others want in a libc. That said, we do
> believe that the effort will still be directly beneficial and usable for
> the broader LLVM community, and may serve as a starting point for others in
> the community to flesh out an increasingly complete set of libc
> functionality.
>
> We are still in the early stages, but we do have some high-level goals and
> guiding principles of the initial scope we are interested in pursuing:
>
>
>    1.
>
>    The project should mesh with the "as a library" philosophy of
the LLVM
>    project: even though "the C Standard Library" is nominally
"a library,"
>    most implementations are, in practice, quite monolithic.
>    2.
>
>    The libc should support static non-PIE and static-PIE linking. This
>    means, providing the CRT (the C runtime) and a PIE loader for static
>    non-PIE and static-PIE linked executables.
>    3.
>
>    If there is a specification, we should follow it. The scope that we
>    need includes most of the C Standard Library; POSIX additions; and some
>    necessary, system-specific extensions. This does not mean we should (or
>    can) follow the entire specification -- there will be some parts which
>    simply aren't worth implementing, and some parts which cannot be
safely
>    used in modern coding practice.
>    4.
>
>    Vendor extensions must be considered very carefully, and only admitted
>    when necessary. Similar to Clang and libc++, it does seem inevitable
that
>    we will need to provide some level of compatibility with other
vendors'
>    extensions.
>    5.
>
>    The project should be an exemplar of developing with LLVM tooling. Two
>    examples are fuzz testing from the start, and sanitizer-supported
testing.
>
>
> There are also few areas which we do not intend to invest in at this point:
>
>
>    1.
>
>    Implement dynamic loading and linking support.
>    2.
>
>    Support for more architectures (we'll start with just x86-64 for
>    simplicity).
>
>
> For these areas, the community is of course free to contribute. Our hope
> is that, preserving the "as a library" design philosophy will
make such
> extensions easy, and allow retaining the simplicity when these features
> aren't needed.
>
> We intend to build the new libc in a gradual manner. To begin with,  the
> new libc will be a layer sitting between the application and the system
> libc. Eventually, when the implementation is sufficiently complete, it will
> be able to replace the system libc at least for some use cases and
contexts.
>
> So, what do you think about incorporating this new libc under the LLVM
> project?
>
> Thank you,
>
> Siva Chandra and the rest of the Google LLVM contributors
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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