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7da5357aca
In PIC mode we were previously computing global variable addresses (or GOT entry addresses) by adding the PC, the PC-relative GOT displacement and the GOT-relative symbol/GOT entry displacement. Because the latter two displacements are fixed, we ended up performing one more addition than necessary. This change causes us to compute addresses using a single PC-relative displacement, resulting in a shorter code sequence. This reduces code size by about 4% in a recent build of Chromium for Android. As a result of this change we no longer need to compute the GOT base address in the ARM backend, which allows us to remove the Global Base Reg pass and SDAG lowering for the GOT. We also now no longer use the GOT when addressing a symbol which is known to be defined in the same linkage unit. Specifically, the symbol must have either hidden visibility or a strong definition in the current module in order to not use the the GOT. This is a change from the previous behaviour where we would use the GOT to address externally visible symbols defined in the same module. I think the only cases where this could matter are cases involving symbol interposition, but we don't really support that well anyway. Differential Revision: http://reviews.llvm.org/D13650 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251322 91177308-0d34-0410-b5e6-96231b3b80d8
260 lines
7.8 KiB
C++
260 lines
7.8 KiB
C++
//===-- ARMELFObjectWriter.cpp - ARM ELF Writer ---------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#include "MCTargetDesc/ARMMCTargetDesc.h"
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#include "MCTargetDesc/ARMFixupKinds.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/StringSwitch.h"
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#include "llvm/MC/MCELFObjectWriter.h"
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#include "llvm/MC/MCExpr.h"
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#include "llvm/MC/MCSectionELF.h"
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#include "llvm/MC/MCValue.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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namespace {
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class ARMELFObjectWriter : public MCELFObjectTargetWriter {
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enum { DefaultEABIVersion = 0x05000000U };
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unsigned GetRelocTypeInner(const MCValue &Target,
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const MCFixup &Fixup,
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bool IsPCRel) const;
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public:
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ARMELFObjectWriter(uint8_t OSABI);
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~ARMELFObjectWriter() override;
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unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
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bool IsPCRel) const override;
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bool needsRelocateWithSymbol(const MCSymbol &Sym,
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unsigned Type) const override;
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};
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}
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ARMELFObjectWriter::ARMELFObjectWriter(uint8_t OSABI)
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: MCELFObjectTargetWriter(/*Is64Bit*/ false, OSABI,
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ELF::EM_ARM,
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/*HasRelocationAddend*/ false) {}
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ARMELFObjectWriter::~ARMELFObjectWriter() {}
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bool ARMELFObjectWriter::needsRelocateWithSymbol(const MCSymbol &Sym,
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unsigned Type) const {
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// FIXME: This is extremely conservative. This really needs to use a
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// whitelist with a clear explanation for why each realocation needs to
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// point to the symbol, not to the section.
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switch (Type) {
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default:
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return true;
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case ELF::R_ARM_PREL31:
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case ELF::R_ARM_ABS32:
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return false;
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}
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}
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// Need to examine the Fixup when determining whether to
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// emit the relocation as an explicit symbol or as a section relative
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// offset
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unsigned ARMELFObjectWriter::GetRelocType(const MCValue &Target,
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const MCFixup &Fixup,
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bool IsPCRel) const {
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return GetRelocTypeInner(Target, Fixup, IsPCRel);
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}
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unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
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const MCFixup &Fixup,
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bool IsPCRel) const {
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MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
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unsigned Type = 0;
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if (IsPCRel) {
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switch ((unsigned)Fixup.getKind()) {
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default:
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report_fatal_error("unsupported relocation on symbol");
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return ELF::R_ARM_NONE;
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case FK_Data_4:
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switch (Modifier) {
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default: llvm_unreachable("Unsupported Modifier");
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case MCSymbolRefExpr::VK_None:
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Type = ELF::R_ARM_REL32;
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break;
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case MCSymbolRefExpr::VK_TLSGD:
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llvm_unreachable("unimplemented");
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case MCSymbolRefExpr::VK_GOTTPOFF:
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Type = ELF::R_ARM_TLS_IE32;
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break;
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case MCSymbolRefExpr::VK_ARM_GOT_PREL:
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Type = ELF::R_ARM_GOT_PREL;
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break;
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}
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break;
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case ARM::fixup_arm_blx:
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case ARM::fixup_arm_uncondbl:
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switch (Modifier) {
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case MCSymbolRefExpr::VK_PLT:
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Type = ELF::R_ARM_CALL;
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break;
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case MCSymbolRefExpr::VK_ARM_TLSCALL:
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Type = ELF::R_ARM_TLS_CALL;
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break;
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default:
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Type = ELF::R_ARM_CALL;
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break;
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}
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break;
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case ARM::fixup_arm_condbl:
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case ARM::fixup_arm_condbranch:
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case ARM::fixup_arm_uncondbranch:
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Type = ELF::R_ARM_JUMP24;
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break;
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case ARM::fixup_t2_condbranch:
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case ARM::fixup_t2_uncondbranch:
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Type = ELF::R_ARM_THM_JUMP24;
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break;
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case ARM::fixup_arm_movt_hi16:
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Type = ELF::R_ARM_MOVT_PREL;
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break;
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case ARM::fixup_arm_movw_lo16:
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Type = ELF::R_ARM_MOVW_PREL_NC;
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break;
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case ARM::fixup_t2_movt_hi16:
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Type = ELF::R_ARM_THM_MOVT_PREL;
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break;
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case ARM::fixup_t2_movw_lo16:
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Type = ELF::R_ARM_THM_MOVW_PREL_NC;
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break;
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case ARM::fixup_arm_thumb_bl:
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case ARM::fixup_arm_thumb_blx:
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switch (Modifier) {
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case MCSymbolRefExpr::VK_ARM_TLSCALL:
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Type = ELF::R_ARM_THM_TLS_CALL;
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break;
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default:
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Type = ELF::R_ARM_THM_CALL;
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break;
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}
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break;
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}
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} else {
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switch ((unsigned)Fixup.getKind()) {
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default:
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report_fatal_error("unsupported relocation on symbol");
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return ELF::R_ARM_NONE;
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case FK_Data_1:
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switch (Modifier) {
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default: llvm_unreachable("unsupported Modifier");
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case MCSymbolRefExpr::VK_None:
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Type = ELF::R_ARM_ABS8;
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break;
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}
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break;
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case FK_Data_2:
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switch (Modifier) {
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default: llvm_unreachable("unsupported modifier");
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case MCSymbolRefExpr::VK_None:
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Type = ELF::R_ARM_ABS16;
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break;
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}
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break;
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case FK_Data_4:
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switch (Modifier) {
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default: llvm_unreachable("Unsupported Modifier");
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case MCSymbolRefExpr::VK_ARM_NONE:
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Type = ELF::R_ARM_NONE;
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break;
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case MCSymbolRefExpr::VK_GOT:
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Type = ELF::R_ARM_GOT_BREL;
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break;
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case MCSymbolRefExpr::VK_TLSGD:
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Type = ELF::R_ARM_TLS_GD32;
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break;
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case MCSymbolRefExpr::VK_TPOFF:
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Type = ELF::R_ARM_TLS_LE32;
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break;
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case MCSymbolRefExpr::VK_GOTTPOFF:
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Type = ELF::R_ARM_TLS_IE32;
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break;
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case MCSymbolRefExpr::VK_None:
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Type = ELF::R_ARM_ABS32;
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break;
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case MCSymbolRefExpr::VK_GOTOFF:
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Type = ELF::R_ARM_GOTOFF32;
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break;
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case MCSymbolRefExpr::VK_ARM_GOT_PREL:
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Type = ELF::R_ARM_GOT_PREL;
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break;
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case MCSymbolRefExpr::VK_ARM_TARGET1:
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Type = ELF::R_ARM_TARGET1;
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break;
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case MCSymbolRefExpr::VK_ARM_TARGET2:
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Type = ELF::R_ARM_TARGET2;
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break;
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case MCSymbolRefExpr::VK_ARM_PREL31:
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Type = ELF::R_ARM_PREL31;
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break;
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case MCSymbolRefExpr::VK_ARM_SBREL:
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Type = ELF::R_ARM_SBREL32;
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break;
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case MCSymbolRefExpr::VK_ARM_TLSLDO:
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Type = ELF::R_ARM_TLS_LDO32;
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break;
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case MCSymbolRefExpr::VK_ARM_TLSCALL:
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Type = ELF::R_ARM_TLS_CALL;
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break;
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case MCSymbolRefExpr::VK_ARM_TLSDESC:
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Type = ELF::R_ARM_TLS_GOTDESC;
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break;
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case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ:
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Type = ELF::R_ARM_TLS_DESCSEQ;
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break;
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}
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break;
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case ARM::fixup_arm_ldst_pcrel_12:
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case ARM::fixup_arm_pcrel_10:
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case ARM::fixup_arm_adr_pcrel_12:
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case ARM::fixup_arm_thumb_bl:
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case ARM::fixup_arm_thumb_cb:
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case ARM::fixup_arm_thumb_cp:
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case ARM::fixup_arm_thumb_br:
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llvm_unreachable("Unimplemented");
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case ARM::fixup_arm_condbranch:
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case ARM::fixup_arm_uncondbranch:
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Type = ELF::R_ARM_JUMP24;
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break;
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case ARM::fixup_arm_movt_hi16:
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Type = ELF::R_ARM_MOVT_ABS;
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break;
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case ARM::fixup_arm_movw_lo16:
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Type = ELF::R_ARM_MOVW_ABS_NC;
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break;
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case ARM::fixup_t2_movt_hi16:
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Type = ELF::R_ARM_THM_MOVT_ABS;
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break;
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case ARM::fixup_t2_movw_lo16:
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Type = ELF::R_ARM_THM_MOVW_ABS_NC;
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break;
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}
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}
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return Type;
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}
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MCObjectWriter *llvm::createARMELFObjectWriter(raw_pwrite_stream &OS,
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uint8_t OSABI,
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bool IsLittleEndian) {
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MCELFObjectTargetWriter *MOTW = new ARMELFObjectWriter(OSABI);
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return createELFObjectWriter(MOTW, OS, IsLittleEndian);
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}
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