a2d8743cc8
This implements Fast-Forward Sequences documented in ARM64EC ABI https://learn.microsoft.com/en-us/windows/arm/arm64ec-abi. There are two conditions when linker should generate such thunks: - For each exported ARM64EC functions. It applies only to ARM64EC functions (we may also have pure x64 functions, for which no thunk is needed). MSVC linker creates `EXP+<mangled export name>` symbol in those cases that points to the thunk and uses that symbol for the export. It's observable from the module: it's possible to reference such symbols as I did in the test. Note that it uses export name, not name of the symbol that's exported (as in `foo` in `/EXPORT:foo=bar`). This implies that if the same function is exported multiple times, it will have multiple thunks. I followed this MSVC behavior. - For hybrid_patchable functions. The linker tries to generate a thunk for each undefined `EXP+*` symbol (and such symbols are created by the compiler as a target of weak alias from the demangled name). MSVC linker tries to find corresponding `*$hp_target` symbol and if fails to do so, it outputs a cryptic error like `LINK : fatal error LNK1000: Internal error during IMAGE::BuildImage`. I just skip generating the thunk in such case (which causes undefined reference error). MSVC linker additionally checks that the symbol complex type is a function (see also #102898). We generally don't do such checks in LLD, so I made it less strict. It should be fine: if it's some data symbol, it will not have `$hp_target` symbol, so we will skip it anyway.
LLVM Linker (lld)
This directory and its subdirectories contain source code for the LLVM Linker, a modular cross platform linker which is built as part of the LLVM compiler infrastructure project.
lld is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt.
Benchmarking
In order to make sure various developers can evaluate patches over the same tests, we create a collection of self contained programs.
It is hosted at https://s3-us-west-2.amazonaws.com/linker-tests/lld-speed-test.tar.xz
The current sha256 is 10eec685463d5a8bbf08d77f4ca96282161d396c65bd97dc99dbde644a31610f.