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
0999cbd0b9 (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 ----------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/MC/MCELFObjectWriter.h"
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using namespace llvm;
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MCELFObjectTargetWriter::MCELFObjectTargetWriter(bool Is64Bit_, uint8_t OSABI_,
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uint16_t EMachine_,
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bool HasRelocationAddend_,
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uint8_t ABIVersion_)
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: OSABI(OSABI_), ABIVersion(ABIVersion_), EMachine(EMachine_),
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HasRelocationAddend(HasRelocationAddend_), Is64Bit(Is64Bit_) {}
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bool MCELFObjectTargetWriter::needsRelocateWithSymbol(const MCValue &,
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const MCSymbol &,
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unsigned Type) const {
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return false;
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}
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void
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MCELFObjectTargetWriter::sortRelocs(const MCAssembler &Asm,
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std::vector<ELFRelocationEntry> &Relocs) {
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}
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void MCELFObjectTargetWriter::addTargetSectionFlags(MCContext &Ctx,
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MCSectionELF &Sec) {}
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