tree a1377acdf1fe81ac8ce84db288d2cdaaf1130d80
parent 7f1271a90589f0cab2ed235231477bb48c23e4d6
author Ryan Prichard <rprichard@google.com> 1546992599 +0000
committer Pirama Arumuga Nainar <pirama@google.com> 1547601946 -0800

[ARM][AArch64] Increase TLS alignment to reserve space for Android's TCB

ARM and AArch64 use TLS variant 1, where the first two words after the
thread pointer are reserved for the TCB, followed by the executable's TLS
segment. Both the thread pointer and the TLS segment are aligned to at
least the TLS segment's alignment.

Android/Bionic historically has not supported ELF TLS, and it has
allocated memory after the thread pointer for several Bionic TLS slots
(currently 9 but soon only 8). At least one of these allocations
(TLS_SLOT_STACK_GUARD == 5) is widespread throughout Android/AArch64
binaries and can't be changed.

To reconcile this disagreement about TLS memory layout, set the minimum
alignment for executable TLS segments to 8 words on ARM/AArch64, which
reserves at least 8 words of memory after the TP (2 for the ABI-specified
TCB and 6 for alignment padding). For simplicity, and because lld doesn't
know when it's targeting Android, increase the alignment regardless of
operating system.

Differential Revision: https://reviews.llvm.org/D53906

Change-Id: If37322cbf6525e4b31ba200201308e4d0ff4c4e4
git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@350681 91177308-0d34-0410-b5e6-96231b3b80d8