5be7f2a943
Assemblers change certain relocations referencing a local symbol to reference the section symbol instead. This conversion is disabled for many conditions (`shouldRelocateWithSymbol`), e.g. TLS symbol, for most targets (including AArch32, x86, PowerPC, and RISC-V) GOT-generating relocations. However, AArch64 encodes the GOT-generating intent in MCValue::RefKind instead of MCSymbolRef::Kind (see commit 0999cbd0b9ed8aa893cce10d681dec6d54b200ad (2014)), therefore not affected by the code `case MCSymbolRefExpr::VK_GOT:`. As GNU ld and ld.lld create GOT entries based on the symbol, ignoring addend, the two ldr instructions will share the same GOT entry, which is not expected: ``` ldr x1, [x1, :got_lo12:x] // converted to .data+0 ldr x1, [x1, :got_lo12:y] // converted to .data+4 .data // .globl x, y would suppress STT_SECTION conversion x: .zero 4 y: .long 42 ``` This patch changes AArch64 to suppress local symbol to STT_SECTION conversion for GOT relocations, matching most other targets. x and y will use different GOT entries, which IMO is the most sensable behavior. With this change, the ABI decision on https://github.com/ARM-software/abi-aa/issues/217 will only affect relocations explicitly referencing STT_SECTION symbols, e.g. ``` ldr x1, [x1, :got_lo12:(.data+0)] ldr x1, [x1, :got_lo12:(.data+4)] // I consider this unreasonable uses ``` IMO all reasonable use cases are unaffected. Link: https://github.com/llvm/llvm-project/issues/63418 GNU assembler PR: https://sourceware.org/bugzilla/show_bug.cgi?id=30788 Reviewed By: peter.smith Differential Revision: https://reviews.llvm.org/D158577
33 lines
1.4 KiB
C++
33 lines
1.4 KiB
C++
//===-- MCELFObjectTargetWriter.cpp - ELF Target Writer Subclass ----------===//
|
|
//
|
|
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
|
|
// See https://llvm.org/LICENSE.txt for license information.
|
|
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "llvm/MC/MCELFObjectWriter.h"
|
|
|
|
using namespace llvm;
|
|
|
|
MCELFObjectTargetWriter::MCELFObjectTargetWriter(bool Is64Bit_, uint8_t OSABI_,
|
|
uint16_t EMachine_,
|
|
bool HasRelocationAddend_,
|
|
uint8_t ABIVersion_)
|
|
: OSABI(OSABI_), ABIVersion(ABIVersion_), EMachine(EMachine_),
|
|
HasRelocationAddend(HasRelocationAddend_), Is64Bit(Is64Bit_) {}
|
|
|
|
bool MCELFObjectTargetWriter::needsRelocateWithSymbol(const MCValue &,
|
|
const MCSymbol &,
|
|
unsigned Type) const {
|
|
return false;
|
|
}
|
|
|
|
void
|
|
MCELFObjectTargetWriter::sortRelocs(const MCAssembler &Asm,
|
|
std::vector<ELFRelocationEntry> &Relocs) {
|
|
}
|
|
|
|
void MCELFObjectTargetWriter::addTargetSectionFlags(MCContext &Ctx,
|
|
MCSectionELF &Sec) {}
|