commit 0a49d36eee0f66cf76a7ab356ed884123be5fcf5
author Peter Smith <peter.smith@linaro.org> Mon Sep 16 09:38:38 2019 +0000
committer Peter Smith <peter.smith@linaro.org> Mon Sep 16 09:38:38 2019 +0000
tree 89532e555a410cfb7009ad3933f3525df7855961
parent b9d863c6c9289df2505f27aedd444a9c389f0087

[ELF][ARM] Implement --fix-cortex-a8 to fix erratum 657417

The --fix-cortex-a8 option implements a linker workaround for the
coretex-a8 erratum 657417. A summary of the erratum conditions is:
- A 32-bit Thumb-2 branch instruction B.w, Bcc.w, BL, BLX spans two
4KiB regions.
- The destination of the branch is to the first 4KiB region.
- The instruction before the branch is a 32-bit Thumb-2 non-branch
instruction.

The linker fix is to redirect the branch to a patch not in the first
4KiB region. The patch forwards the branch on to its target.

The cortex-a8, is an old CPU, with the first implementation of this
workaround in ld.bfd appearing in 2009. The cortex-a8 has been used in
early Android Phones and there are some critical applications that still
need to run on a cortex-a8 that have the erratum. The patch is applied
roughly 10 times on LLD and 20 on Clang when they are built with
--fix-cortex-a8 on an Arm system.

The formal erratum description is avaliable in the ARM Core Cortex-A8
(AT400/AT401) Errata Notice document. This is available from Arm on
request but it seems to be findable via a web search.

Differential Revision: https://reviews.llvm.org/D67284



git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@371965 91177308-0d34-0410-b5e6-96231b3b80d8