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diff --git a/llvm/docs/Proposals/LLVMLibC.rst b/llvm/docs/Proposals/LLVMLibC.rst deleted file mode 100644 index e113e7b..0000000 --- a/llvm/docs/Proposals/LLVMLibC.rst +++ /dev/null @@ -1,125 +0,0 @@ -============================== -"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. |