mirror of
https://github.com/RPCS3/llvm-mirror.git
synced 2024-11-24 19:52:54 +01:00
2cf884bb0b
Reviewers: chandlerc, dlj, echristo, hfinkel, jfb, zturner Subscribers: dexonsmith, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D64939 llvm-svn: 369012
126 lines
5.4 KiB
ReStructuredText
126 lines
5.4 KiB
ReStructuredText
==============================
|
|
"llvm-libc" C Standard Library
|
|
==============================
|
|
|
|
.. contents:: Table of Contents
|
|
:depth: 4
|
|
:local:
|
|
|
|
Introduction
|
|
============
|
|
|
|
This is a proposal to start *llvm-libc*, an implementation of the
|
|
C standard library targeting C17 and above, as part of the LLVM project.
|
|
llvm-libc will also provide platform specific extensions as relevant.
|
|
For example, on Linux it also provides pthreads, librt and other POSIX
|
|
extension libraries.
|
|
|
|
Features
|
|
========
|
|
|
|
llvm-libc will be developed to have a certain minimum set of features:
|
|
|
|
- C17 and upwards conformant.
|
|
- A modular libc with individual pieces implemented in the "as a
|
|
library" philosophy of the LLVM project.
|
|
- Ability to layer this libc over the system libc if possible and desired
|
|
for a platform.
|
|
- Provide C symbols as specified by the standards, but take advantage
|
|
and use C++ language facilities for the core implementation.
|
|
- Provides POSIX extensions on POSIX compliant platforms.
|
|
- Provides system-specific extensions as appropriate. For example,
|
|
provides the Linux API on Linux.
|
|
- Vendor extensions if and only if necessary.
|
|
- Designed and developed from the start to work with LLVM tooling and
|
|
testing like fuzz testing and sanitizer-supported testing.
|
|
- ABI independent implementation as far as possible.
|
|
- Use source based implementations as far possible rather than
|
|
assembly. Will try to *fix* the compiler rather than use assembly
|
|
language workarounds.
|
|
- Extensive unit testing and standards conformance testing. If relevant
|
|
and possible, differential testing: We want to be able
|
|
to test llvm-libc against another battle-tested libc. This is
|
|
essentially to understand how we differ from other libcs. Also if
|
|
relevant and possible, test against the testsuite of an another
|
|
battle-tested libc implementation.
|
|
|
|
Why a new C Standard Library?
|
|
=============================
|
|
|
|
Implementing a libc is no small task and is not be taken lightly. A
|
|
natural question to ask is, "why a new implementation of the C
|
|
standard library?" There is no single answer to this question, but
|
|
some of the major reasons are as follows:
|
|
|
|
- Most libc implementations are monolithic. It is a non-trivial
|
|
porting task to pick and choose only the pieces relevant to one's
|
|
platform. The llvm-libc will be developed with sufficient modularity to
|
|
make picking and choosing a straightforward task.
|
|
- Most libc implementations break when built with sanitizer specific
|
|
compiler options. The llvm-libc will be developed from the start to
|
|
work with those specialized compiler options.
|
|
- The llvm-libc will be developed to support and employ fuzz testing
|
|
from the start.
|
|
- Most libc implementations use a good amount of assembly language,
|
|
and assume specific ABIs (may be platform dependent). With the llvm-libc
|
|
implementation, we want to use normal source code as much as possible so
|
|
that compiler-based changes to the ABI are easy. Moreover, as part of the
|
|
LLVM project, we want to use this opportunity to fix performance related
|
|
compiler bugs rather than using assembly workarounds.
|
|
- A large hole in the LLVM toolchain will be plugged with llvm-libc.
|
|
With the broad platform expertise in the LLVM community, and the
|
|
strong license and project structure, we think that llvm-libc will
|
|
be more tunable and robust, without sacrificing the simplicity and
|
|
accessibility typical of the LLVM project.
|
|
|
|
Platform Support
|
|
================
|
|
|
|
We envision that llvm-libc will support a variety of platforms in the coming
|
|
years. Interested parties are encouraged to participate in the design and
|
|
implementation, and add support for their favorite platforms.
|
|
|
|
ABI Compatibility
|
|
=================
|
|
|
|
As llvm-libc is new, it will not offer ABI stability in the initial stages.
|
|
However, as we've heard from other LLVM contributors that they are interested
|
|
in having ABI stability, llvm-libc code will be written in a manner which is
|
|
amenable to ABI stability. We are looking for contributors interested in
|
|
driving the design in this space to help us define what exactly does ABI
|
|
stability mean for llvm-libc.
|
|
|
|
Layering Over Another libc
|
|
==========================
|
|
|
|
When meaningful and practically possible on a platform, llvm-libc will be
|
|
developed in a fashion that it will be possible to layer it over the system
|
|
libc. This does not mean that one can mix llvm-libc with the system-libc. Also,
|
|
it does not mean that layering is the only way to use llvm-libc. What it
|
|
means is that, llvm-libc can optionally be packaged in a way that it can
|
|
delegate parts of the functionality to the system-libc. The delegation happens
|
|
internal to llvm-libc and is invisible to the users. From the user's point of
|
|
view, they only call into llvm-libc.
|
|
|
|
There are a few problems one needs to be mindful of when implementing such a
|
|
delegation scheme in llvm-libc. Examples of such problems are:
|
|
|
|
1. One cannot mix data structures from llvm-libc with those from the
|
|
system-libc. A translation from one set of data structures to the other should
|
|
happen internal to llvm-libc.
|
|
2. The delegation mechanism has to be implemented over a related set of
|
|
functions. For example, one cannot delegate just the `fopen` function to the
|
|
system-libc. One will have to delegate all `FILE` related functions to the
|
|
system-libc.
|
|
|
|
Current Status
|
|
==============
|
|
|
|
llvm-libc development is still in the planning phase.
|
|
|
|
Build Bots
|
|
==========
|
|
|
|
Once the development starts, there will be llvm-libc focused builders added to
|
|
the LLVM BuildBot.
|