Merging r361090:

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r361090 | maskray | 2019-05-17 20:16:00 -0700 (Fri, 17 May 2019) | 34 lines

[ARM][AArch64] Revert Android Bionic PT_TLS overaligning hack

This reverts D53906.

D53906 increased p_align of PT_TLS on ARM/AArch64 to 32/64 to make the
static TLS layout compatible with Android Bionic's ELF TLS. However,
this may cause glibc ARM/AArch64 programs to crash (see PR41527).

The faulty PT_TLS in the executable satisfies p_vaddr%p_align != 0. The
remainder is normally 0 but may be non-zero with the hack in place. The
problem is that we increase PT_TLS's p_align after OutputSections'
addresses are fixed (assignAddress()). It is possible that
p_vaddr%old_p_align = 0 while p_vaddr%new_p_align != 0.

For a thread local variable defined in the executable, lld computed TLS
offset (local exec) is different from glibc computed TLS offset from
another module (initial exec/generic dynamic). Note: PR41527 said the
bug affects initial exec but actually generic dynamic is affected as
well.

(glibc is correct in that it compute offsets that satisfy
`offset%p_align == p_vaddr%p_align`, which is a basic ELF requirement.
This hack appears to work on FreeBSD rtld, musl<=1.1.22, and Bionic, but
that is just because they (and lld) incorrectly compute offsets that
satisfy `offset%p_align = 0` instead.)

Android developers are fine to revert this patch, carry this patch in
their tree before figuring out a long-term solution (e.g. a dummy .tdata
with sh_addralign=64 sh_size={0,1} in crtbegin*.o files. The overhead is
now insignificant after D62059).

Reviewed By: rprichard, srhines

Differential Revision: https://reviews.llvm.org/D62055
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git-svn-id: https://llvm.org/svn/llvm-project/lld/branches/release_80@362858 91177308-0d34-0410-b5e6-96231b3b80d8
9 files changed
tree: 03b5f3c52034b98c5549b05e7c57b7c679a95f54
  1. .arcconfig
  2. .clang-format
  3. .gitignore
  4. CMakeLists.txt
  5. CODE_OWNERS.TXT
  6. COFF/
  7. Common/
  8. ELF/
  9. LICENSE.TXT
  10. MinGW/
  11. README.md
  12. cmake/
  13. docs/
  14. include/
  15. lib/
  16. test/
  17. tools/
  18. unittests/
  19. utils/
  20. wasm/
README.md

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.