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c77659e549
This patch provides two major changes: 1. Add getRelocationInfo to check if a constant will have static, dynamic, or no relocations. (Also rename the original needsRelocation to needsDynamicRelocation.) 2. Only allow a constant with no relocations (static or dynamic) to be placed in a mergeable section. This will allow unused symbols that contain static relocations and happen to fit in mergeable constant sections (.rodata.cstN) to instead be placed in unique-named sections if -fdata-sections is used and subsequently garbage collected by --gc-sections. See https://lists.llvm.org/pipermail/llvm-dev/2021-February/148281.html. Differential Revision: https://reviews.llvm.org/D95960
60 lines
2.5 KiB
C++
60 lines
2.5 KiB
C++
//===-- PPCTargetObjectFile.cpp - PPC Object Info -------------------------===//
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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 "PPCTargetObjectFile.h"
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#include "llvm/IR/GlobalVariable.h"
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#include "llvm/IR/Mangler.h"
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#include "llvm/MC/MCContext.h"
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#include "llvm/MC/MCExpr.h"
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#include "llvm/MC/MCSectionELF.h"
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using namespace llvm;
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void
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PPC64LinuxTargetObjectFile::
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Initialize(MCContext &Ctx, const TargetMachine &TM) {
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TargetLoweringObjectFileELF::Initialize(Ctx, TM);
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}
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MCSection *PPC64LinuxTargetObjectFile::SelectSectionForGlobal(
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const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
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// Here override ReadOnlySection to DataRelROSection for PPC64 SVR4 ABI
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// when we have a constant that contains global relocations. This is
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// necessary because of this ABI's handling of pointers to functions in
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// a shared library. The address of a function is actually the address
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// of a function descriptor, which resides in the .opd section. Generated
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// code uses the descriptor directly rather than going via the GOT as some
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// other ABIs do, which means that initialized function pointers must
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// reference the descriptor. The linker must convert copy relocs of
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// pointers to functions in shared libraries into dynamic relocations,
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// because of an ordering problem with initialization of copy relocs and
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// PLT entries. The dynamic relocation will be initialized by the dynamic
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// linker, so we must use DataRelROSection instead of ReadOnlySection.
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// For more information, see the description of ELIMINATE_COPY_RELOCS in
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// GNU ld.
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if (Kind.isReadOnly()) {
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const auto *GVar = dyn_cast<GlobalVariable>(GO);
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if (GVar && GVar->isConstant() &&
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GVar->getInitializer()->needsDynamicRelocation())
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Kind = SectionKind::getReadOnlyWithRel();
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}
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return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
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}
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const MCExpr *PPC64LinuxTargetObjectFile::
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getDebugThreadLocalSymbol(const MCSymbol *Sym) const {
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const MCExpr *Expr =
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MCSymbolRefExpr::create(Sym, MCSymbolRefExpr::VK_DTPREL, getContext());
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return MCBinaryExpr::createAdd(Expr,
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MCConstantExpr::create(0x8000, getContext()),
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getContext());
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}
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