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Don't omit dynamic relocations for the GOT.

Where Clang's AArch64 backend seems to differ from the X86 backend is
that it tends to use the GOT more aggressively.

After getting CloudABI PIEs working on x86-64, I noticed that accessing
global variables would still crash on aarch64. Tracing it down, it turns
out that the GOT was filled with entries assuming the base address was
zero.

It turns out that we skip generating relocations for GOT entries in case
the relocation pointing towards the GOT is relative. Whether the thing
pointing to the GOT is absolute or relative shouldn't make any
difference; the GOT entry itself should contain the absolute address,
thus needs a relocation regardless.

Approved by:	rafael
Differential Revision:	http://reviews.llvm.org/D18739


git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@265453 91177308-0d34-0410-b5e6-96231b3b80d8
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EdSchouten committed Apr 5, 2016
1 parent eef6997 commit 519bbfb5b3fb1f21866e10abece919ecfbfba678
Showing with 22 additions and 3 deletions.
  1. +1 −3 ELF/Writer.cpp
  2. +21 −0 test/ELF/aarch64-got-relocations.s
@@ -432,9 +432,7 @@ void Writer<ELFT>::scanRelocs(InputSectionBase<ELFT> &C, ArrayRef<RelTy> Rels) {
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
continue;

bool Dynrel = Config->Pic && !Target->isRelRelative(Type) &&
!Target->isSizeRel(Type);
if (Preemptible || Dynrel) {
if (Preemptible || Config->Pic) {
uint32_t DynType;
if (Body.isTls())
DynType = Target->TlsGotRel;
@@ -0,0 +1,21 @@
# REQUIRES: aarch64
# RUN: llvm-mc -filetype=obj -triple=aarch64-unknown-cloudabi %s -o %t.o
# RUN: ld.lld -pie %t.o -o %t
# RUN: llvm-readobj -r %t | FileCheck %s

# If we're addressing a global relatively through the GOT, we still need to
# emit a relocation for the entry in the GOT itself.
# CHECK: Relocations [
# CHECK: Section (4) .rela.dyn {
# CHECK: 0x{{[0-9A-F]+}} R_AARCH64_RELATIVE - 0x{{[0-9A-F]+}}
# CHECK: }
# CHECK: ]

.globl _start
.type _start,@function
_start:
adrp x8, :got:i
ldr x8, [x8, :got_lo12:i]

.type i,@object
.comm i,4,4

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