| commit | 97a58b04c6813d8cab1bfb47ce5023895b016319 | [log] [tgz] |
|---|---|---|
| author | Daniel Paoliello <danpao@microsoft.com> | Fri May 09 14:56:38 2025 -0700 |
| committer | GitHub <noreply@github.com> | Fri May 09 14:56:38 2025 -0700 |
| tree | 802dde382a01b909ee5571573823d753d0aee20e | |
| parent | 829395591ebf248a9fb57dbed6a8383db4ba6e00 [diff] |
[aarch64][x86][win] Add compiler support for MSVC's /funcoverride flag (Windows kernel loader replaceable functions) (#125320) Adds support for MSVC's undocumented `/funcoverride` flag, which marks functions as being replaceable by the Windows kernel loader. This is used to allow functions to be upgraded depending on the capabilities of the current processor (e.g., the kernel can be built with the naive implementation of a function, but that function can be replaced at boot with one that uses SIMD instructions if the processor supports them). For each marked function we need to generate: * An undefined symbol named `<name>_$fo$`. * A defined symbol `<name>_$fo_default$` that points to the `.data` section (anywhere in the data section, it is assumed to be zero sized). * An `/ALTERNATENAME` linker directive that points from `<name>_$fo$` to `<name>_$fo_default$`. This is used by the MSVC linker to generate the appropriate metadata in the Dynamic Value Relocation Table. Marked function must never be inlined (otherwise those inline sites can't be replaced). Note that I've chosen to implement this in AsmPrinter as there was no way to create a `GlobalVariable` for `<name>_$fo$` that would result in a symbol being emitted (as nothing consumes it and it has no initializer). I tried to have `llvm.used` and `llvm.compiler.used` point to it, but this didn't help. Within LLVM I referred to this feature as "loader replaceable" as "function override" already has a different meaning to C++ developers... I also took the opportunity to extract the feature symbol generation code used by both AArch64 and X86 into a common function in AsmPrinter.
Welcome to the LLVM project!
This repository contains the source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and run-time environments.
The LLVM project has multiple components. The core of the project is itself called “LLVM”. This contains all of the tools, libraries, and header files needed to process intermediate representations and convert them into object files. Tools include an assembler, disassembler, bitcode analyzer, and bitcode optimizer.
C-like languages use the Clang frontend. This component compiles C, C++, Objective-C, and Objective-C++ code into LLVM bitcode -- and from there into object files, using LLVM.
Other components include: the libc++ C++ standard library, the LLD linker, and more.
Consult the Getting Started with LLVM page for information on building and running LLVM.
For information on how to contribute to the LLVM project, please take a look at the Contributing to LLVM guide.
Join the LLVM Discourse forums, Discord chat, LLVM Office Hours or Regular sync-ups.
The LLVM project has adopted a code of conduct for participants to all modes of communication within the project.