d45df09435
Summary: While the generic ABI requires notes to be 8-byte aligned in ELF64, many vendor-specific notes (from Linux, NetBSD, Solaris, etc) use 4-byte alignment. In a PT_NOTE segment, if 4-byte aligned notes are followed by an 8-byte aligned note, the possible 4-byte padding may make consumers fail to parse the 8-byte aligned note. See PR41000 for a recent report about .note.gnu.property (NT_GNU_PROPERTY_TYPE_0). (Note, for NT_GNU_PROPERTY_TYPE_0, the consumers should probably migrate to PT_GNU_PROPERTY, but the alignment issue affects other notes as well.) To fix the issue, don't mix notes with different alignments in one PT_NOTE. If compilers emit 4-byte aligned notes before 8-byte aligned notes, we'll create at most 2 segments. sh_size%sh_addralign=0 is actually implied by the rule for linking unrecognized sections (in generic ABI), so we don't have to check that. Notes that match in name, type and attribute flags are concatenated into a single output section. The compilers have to ensure sh_size%sh_addralign=0 to make concatenated notes parsable. An alternative approach is to create a PT_NOTE for each SHT_NOTE, but we'll have to incur the sizeof(Elf64_Phdr)=56 overhead every time a new note section is introduced. Reviewers: ruiu, jakehehrlich, phosek, jhenderson, pcc, espindola Subscribers: emaste, arichardson, krytarowski, fedor.sergeev, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D61296 llvm-svn: 359853
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.