fe83270ee9
SHF_ARM_PURECODE flag when being built with the -mexecute-only flag. All code sections of an ELF must have the flag set for the final .text section to be execute-only, otherwise the flag gets removed. A HasData flag is added to MCSection to aid in the determination that the section is empty. A virtual setTargetSectionFlags is added to MCELFObjectTargetWriter to allow subclasses to set target specific section flags to be added to sections which we then use in the ARM backend to set SHF_ARM_PURECODE. Patch by Ivan Lozano! Reviewed By: echristo Differential Revision: https://reviews.llvm.org/D48792 llvm-svn: 341593
261 lines
8.5 KiB
C++
261 lines
8.5 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/ARMFixupKinds.h"
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#include "MCTargetDesc/ARMMCTargetDesc.h"
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#include "llvm/BinaryFormat/ELF.h"
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#include "llvm/MC/MCContext.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/MCFixup.h"
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#include "llvm/MC/MCObjectFileInfo.h"
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#include "llvm/MC/MCObjectWriter.h"
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#include "llvm/MC/MCValue.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/raw_ostream.h"
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#include <cstdint>
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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, const MCFixup &Fixup,
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bool IsPCRel, MCContext &Ctx) const;
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public:
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ARMELFObjectWriter(uint8_t OSABI);
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~ARMELFObjectWriter() override = default;
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unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
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const MCFixup &Fixup, 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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void addTargetSectionFlags(MCContext &Ctx, MCSectionELF &Sec) override;
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};
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} // end anonymous namespace
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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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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(MCContext &Ctx, 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, Ctx);
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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,
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MCContext &Ctx) const {
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MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant();
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if (IsPCRel) {
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switch ((unsigned)Fixup.getKind()) {
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default:
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Ctx.reportFatalError(Fixup.getLoc(), "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:
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llvm_unreachable("Unsupported Modifier");
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case MCSymbolRefExpr::VK_None:
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return ELF::R_ARM_REL32;
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case MCSymbolRefExpr::VK_GOTTPOFF:
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return ELF::R_ARM_TLS_IE32;
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case MCSymbolRefExpr::VK_ARM_GOT_PREL:
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return ELF::R_ARM_GOT_PREL;
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case MCSymbolRefExpr::VK_ARM_PREL31:
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return ELF::R_ARM_PREL31;
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}
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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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return ELF::R_ARM_CALL;
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case MCSymbolRefExpr::VK_TLSCALL:
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return ELF::R_ARM_TLS_CALL;
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default:
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return ELF::R_ARM_CALL;
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}
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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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return ELF::R_ARM_JUMP24;
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case ARM::fixup_t2_condbranch:
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return ELF::R_ARM_THM_JUMP19;
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case ARM::fixup_t2_uncondbranch:
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return ELF::R_ARM_THM_JUMP24;
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case ARM::fixup_arm_movt_hi16:
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return ELF::R_ARM_MOVT_PREL;
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case ARM::fixup_arm_movw_lo16:
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return ELF::R_ARM_MOVW_PREL_NC;
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case ARM::fixup_t2_movt_hi16:
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return ELF::R_ARM_THM_MOVT_PREL;
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case ARM::fixup_t2_movw_lo16:
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return ELF::R_ARM_THM_MOVW_PREL_NC;
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case ARM::fixup_arm_thumb_br:
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return ELF::R_ARM_THM_JUMP11;
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case ARM::fixup_arm_thumb_bcc:
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return ELF::R_ARM_THM_JUMP8;
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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_TLSCALL:
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return ELF::R_ARM_THM_TLS_CALL;
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default:
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return ELF::R_ARM_THM_CALL;
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}
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}
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}
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switch ((unsigned)Fixup.getKind()) {
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default:
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Ctx.reportFatalError(Fixup.getLoc(), "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:
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llvm_unreachable("unsupported Modifier");
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case MCSymbolRefExpr::VK_None:
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return ELF::R_ARM_ABS8;
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}
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case FK_Data_2:
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switch (Modifier) {
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default:
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llvm_unreachable("unsupported modifier");
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case MCSymbolRefExpr::VK_None:
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return ELF::R_ARM_ABS16;
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}
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case FK_Data_4:
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switch (Modifier) {
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default:
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llvm_unreachable("Unsupported Modifier");
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case MCSymbolRefExpr::VK_ARM_NONE:
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return ELF::R_ARM_NONE;
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case MCSymbolRefExpr::VK_GOT:
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return ELF::R_ARM_GOT_BREL;
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case MCSymbolRefExpr::VK_TLSGD:
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return ELF::R_ARM_TLS_GD32;
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case MCSymbolRefExpr::VK_TPOFF:
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return ELF::R_ARM_TLS_LE32;
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case MCSymbolRefExpr::VK_GOTTPOFF:
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return ELF::R_ARM_TLS_IE32;
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case MCSymbolRefExpr::VK_None:
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return ELF::R_ARM_ABS32;
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case MCSymbolRefExpr::VK_GOTOFF:
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return ELF::R_ARM_GOTOFF32;
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case MCSymbolRefExpr::VK_ARM_GOT_PREL:
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return ELF::R_ARM_GOT_PREL;
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case MCSymbolRefExpr::VK_ARM_TARGET1:
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return ELF::R_ARM_TARGET1;
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case MCSymbolRefExpr::VK_ARM_TARGET2:
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return ELF::R_ARM_TARGET2;
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case MCSymbolRefExpr::VK_ARM_PREL31:
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return ELF::R_ARM_PREL31;
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case MCSymbolRefExpr::VK_ARM_SBREL:
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return ELF::R_ARM_SBREL32;
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case MCSymbolRefExpr::VK_ARM_TLSLDO:
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return ELF::R_ARM_TLS_LDO32;
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case MCSymbolRefExpr::VK_TLSCALL:
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return ELF::R_ARM_TLS_CALL;
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case MCSymbolRefExpr::VK_TLSDESC:
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return ELF::R_ARM_TLS_GOTDESC;
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case MCSymbolRefExpr::VK_TLSLDM:
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return ELF::R_ARM_TLS_LDM32;
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case MCSymbolRefExpr::VK_ARM_TLSDESCSEQ:
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return ELF::R_ARM_TLS_DESCSEQ;
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}
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case ARM::fixup_arm_condbranch:
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case ARM::fixup_arm_uncondbranch:
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return ELF::R_ARM_JUMP24;
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case ARM::fixup_arm_movt_hi16:
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switch (Modifier) {
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default:
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llvm_unreachable("Unsupported Modifier");
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case MCSymbolRefExpr::VK_None:
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return ELF::R_ARM_MOVT_ABS;
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case MCSymbolRefExpr::VK_ARM_SBREL:
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return ELF::R_ARM_MOVT_BREL;
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}
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case ARM::fixup_arm_movw_lo16:
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switch (Modifier) {
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default:
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llvm_unreachable("Unsupported Modifier");
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case MCSymbolRefExpr::VK_None:
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return ELF::R_ARM_MOVW_ABS_NC;
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case MCSymbolRefExpr::VK_ARM_SBREL:
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return ELF::R_ARM_MOVW_BREL_NC;
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}
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case ARM::fixup_t2_movt_hi16:
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switch (Modifier) {
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default:
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llvm_unreachable("Unsupported Modifier");
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case MCSymbolRefExpr::VK_None:
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return ELF::R_ARM_THM_MOVT_ABS;
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case MCSymbolRefExpr::VK_ARM_SBREL:
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return ELF::R_ARM_THM_MOVT_BREL;
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}
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case ARM::fixup_t2_movw_lo16:
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switch (Modifier) {
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default:
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llvm_unreachable("Unsupported Modifier");
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case MCSymbolRefExpr::VK_None:
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return ELF::R_ARM_THM_MOVW_ABS_NC;
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case MCSymbolRefExpr::VK_ARM_SBREL:
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return ELF::R_ARM_THM_MOVW_BREL_NC;
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}
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}
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}
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void ARMELFObjectWriter::addTargetSectionFlags(MCContext &Ctx,
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MCSectionELF &Sec) {
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// The mix of execute-only and non-execute-only at link time is
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// non-execute-only. To avoid the empty implicitly created .text
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// section from making the whole .text section non-execute-only, we
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// mark it execute-only if it is empty and there is at least one
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// execute-only section in the object.
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MCSectionELF *TextSection =
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static_cast<MCSectionELF *>(Ctx.getObjectFileInfo()->getTextSection());
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if (Sec.getKind().isExecuteOnly() && !TextSection->hasInstructions() &&
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!TextSection->hasData()) {
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TextSection->setFlags(TextSection->getFlags() | ELF::SHF_ARM_PURECODE);
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}
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}
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std::unique_ptr<MCObjectTargetWriter>
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llvm::createARMELFObjectWriter(uint8_t OSABI) {
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return llvm::make_unique<ARMELFObjectWriter>(OSABI);
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}
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