07dad4ecba
The behavior of an undefined weak reference is implementation defined.
For static -no-pie linking, dynamic relocations are generally avoided (except
IRELATIVE). -shared linking generally emits dynamic relocations.
Dynamic -no-pie linking and -pie allow flexibility. Changes adjust the
behavior for better consistency and simpler internal representation,
e.g. https://reviews.llvm.org/D63003 https://reviews.llvm.org/D105164
(generalized to undefined non-weak in
2fcaa00d1e).
GNU ld introduced -z [no]dynamic-undefined-weak option to fine-tune the
behavior. (The option is not very effective with -no-pie, e.g. on
x86-64, `ld.bfd a.o s.so -z dynamic-undefined-weak` generates
R_X86_64_NONE relocations instead of GLOB_DAT/JUMP_SLOT)
This patch implements -z [no]dynamic-undefined-weak option.
The effects are summarized as follows:
* Static -no-pie: no-op
* Dynamic -no-pie: nodynamic-undefined-weak suppresses GLOB_DAT/JUMP_SLOT
* Static -pie: dynamic-undefined-weak generates ABS/GLOB_DAT/JUMP_SLOT.
https://discourse.llvm.org/t/lld-weak-undefined-symbols-in-vdso-only/86749
* Dynamic -pie: nodynamic-undefined-weak suppresses ABS/GLOB_DAT/JUMP_SLOT
The -pie behavior likely stays stable while -no-pie (`!ctx.arg.isPic` in
`isStaticLinkTimeConstant`) behavior will likely change in the future.
The current default value of ctx.arg.zDynamicUndefined is selected to
prevent behavior changes.
Pull Request: https://github.com/llvm/llvm-project/pull/143831
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.