171cb8f53f
The prior page was the proposal doc, this one is now more about what the project intends to do, written in the present tense. Reviewed By: sivachandra Differential Revision: https://reviews.llvm.org/D119379
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========================================================
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llvm-libc: An ISO C-conformant Standard Library for LLVM
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========================================================
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**llvm-libc library is not complete. If you need a fully functioning libc right
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now, you should continue to use your standard system libc.**
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.. contents:: Table of Contents
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:depth: 4
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:local:
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Goals
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=====
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- C17 and upwards conformant.
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- A modular libc with individual pieces implemented in the "as a
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library" philosophy of the LLVM project.
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- Ability to layer this libc over the system libc if possible and desired
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for a platform.
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- Provide POSIX extensions on POSIX compliant platforms.
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- Provide system-specific extensions as appropriate. For example,
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provide the Linux API on Linux.
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- Designed and developed from the start to work with LLVM tooling, fuzz testing
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and sanitizer-supported testing.
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- Use source based implementations as far possible rather than
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assembly. Will try to *fix* the compiler rather than use assembly
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language workarounds.
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- Extensive unit testing and standards conformance testing.
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Why a new C Standard Library?
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=============================
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Implementing a libc is no small task and is not be taken lightly. A
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natural question to ask is, "why a new implementation of the C
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standard library?" Some of the major reasons are as follows:
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- Rather than being built as a single monolithic codebase, llvm-libc is designed
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from the beginning to enable picking and choosing pieces. This allows using
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it as a minimum overlay for e.g. faster math functions than might be
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available on the system library. This is useful where an application may
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need to access improved CPU support over what's available on the system,
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or may need guarantees in performance across different installs.
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- Explicit support for building llvm-libc and code with sanitizer compiler
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options.
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- `Fuzzing`__
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- Be useful for research and review. By avoiding assembly language, using C++
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iterators, RAII and templates, llvm-libc aims to have clearly
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readable code and to improve the compiler as needed to ensure that optimal
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assembly is emitted.
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- Enable fully static compiles.
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.. __: https://github.com/llvm/llvm-project/tree/main/libc/fuzzing
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Platform Support
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================
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Most development is currently targeting x86_64 and aarch64 on Linux. Several
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functions in llvm-libc have been tested on Windows. The Fuchsia platform is
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slowly replacing functions from its bundled libc with functions from llvm-libc.
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ABI Compatibility
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=================
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llvm-libc is written to be ABI independent. Interfaces are generated using
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LLVM's tablegen, so supporting arbitrary ABIs is possible. In it's initial
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stages llvm-libc is not offering ABI stability in any form.
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Other Interesting Documentation
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===============================
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.. toctree::
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build_system
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clang_tidy_checks
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entrypoints
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fuzzing
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ground_truth_specification
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header_generation
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implementation_standard
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integration_test
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layering
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mechanics_of_public_api
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redirectors
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source_layout
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