From d70293d1237bde3de460bf487c2ec386328c3f12 Mon Sep 17 00:00:00 2001 From: Eric Christopher Date: Thu, 6 Sep 2018 22:09:31 +0000 Subject: The initial .text section generated in object files was missing the 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 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@341593 91177308-0d34-0410-b5e6-96231b3b80d8 --- include/llvm/MC/MCELFObjectWriter.h | 3 +++ include/llvm/MC/MCSection.h | 7 ++++++ lib/MC/ELFObjectWriter.cpp | 3 +++ lib/MC/MCELFObjectTargetWriter.cpp | 3 +++ lib/MC/MCObjectStreamer.cpp | 6 +++++ lib/MC/MCSection.cpp | 3 ++- lib/Target/ARM/ARMTargetObjectFile.cpp | 14 ++++++++++- lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp | 18 +++++++++++++++ test/CodeGen/ARM/execute-only.ll | 3 +++ test/MC/ARM/elf-execute-only-section.ll | 13 +++++++++++ .../ELF/ARM/execute-only-populated-text-section.s | 27 ++++++++++++++++++++++ test/MC/ELF/ARM/execute-only-section.s | 3 ++- test/MC/ELF/ARM/execute-only-text-section-data.s | 27 ++++++++++++++++++++++ 13 files changed, 127 insertions(+), 3 deletions(-) create mode 100644 test/MC/ARM/elf-execute-only-section.ll create mode 100644 test/MC/ELF/ARM/execute-only-populated-text-section.s create mode 100644 test/MC/ELF/ARM/execute-only-text-section-data.s diff --git a/include/llvm/MC/MCELFObjectWriter.h b/include/llvm/MC/MCELFObjectWriter.h index bff58fef6af..389a4d71b6a 100644 --- a/include/llvm/MC/MCELFObjectWriter.h +++ b/include/llvm/MC/MCELFObjectWriter.h @@ -13,6 +13,7 @@ #include "llvm/ADT/Triple.h" #include "llvm/BinaryFormat/ELF.h" #include "llvm/MC/MCObjectWriter.h" +#include "llvm/MC/MCSectionELF.h" #include "llvm/Support/Casting.h" #include "llvm/Support/raw_ostream.h" #include @@ -90,6 +91,8 @@ public: virtual void sortRelocs(const MCAssembler &Asm, std::vector &Relocs); + virtual void addTargetSectionFlags(MCContext &Ctx, MCSectionELF &Sec); + /// \name Accessors /// @{ uint8_t getOSABI() const { return OSABI; } diff --git a/include/llvm/MC/MCSection.h b/include/llvm/MC/MCSection.h index ba5c60d3ba5..eb210b4e9df 100644 --- a/include/llvm/MC/MCSection.h +++ b/include/llvm/MC/MCSection.h @@ -78,6 +78,10 @@ private: /// Whether this section has had instructions emitted into it. bool HasInstructions : 1; + /// Whether this section has had data emitted into it. + /// Right now this is only used by the ARM backend. + bool HasData : 1; + bool IsRegistered : 1; MCDummyFragment DummyFragment; @@ -137,6 +141,9 @@ public: bool hasInstructions() const { return HasInstructions; } void setHasInstructions(bool Value) { HasInstructions = Value; } + bool hasData() const { return HasData; } + void setHasData(bool Value) { HasData = Value; } + bool isRegistered() const { return IsRegistered; } void setIsRegistered(bool Value) { IsRegistered = Value; } diff --git a/lib/MC/ELFObjectWriter.cpp b/lib/MC/ELFObjectWriter.cpp index 358c036f2a7..5b8b013ad08 100644 --- a/lib/MC/ELFObjectWriter.cpp +++ b/lib/MC/ELFObjectWriter.cpp @@ -29,6 +29,7 @@ #include "llvm/MC/MCFixup.h" #include "llvm/MC/MCFixupKindInfo.h" #include "llvm/MC/MCFragment.h" +#include "llvm/MC/MCObjectFileInfo.h" #include "llvm/MC/MCObjectWriter.h" #include "llvm/MC/MCSection.h" #include "llvm/MC/MCSectionELF.h" @@ -1107,6 +1108,8 @@ uint64_t ELFWriter::writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) { SectionIndexMap[RelSection] = addToSectionTable(RelSection); Relocations.push_back(RelSection); } + + OWriter.TargetObjectWriter->addTargetSectionFlags(Ctx, Section); } MCSectionELF *CGProfileSection = nullptr; diff --git a/lib/MC/MCELFObjectTargetWriter.cpp b/lib/MC/MCELFObjectTargetWriter.cpp index 483ee94c0db..ff53dd7299c 100644 --- a/lib/MC/MCELFObjectTargetWriter.cpp +++ b/lib/MC/MCELFObjectTargetWriter.cpp @@ -26,3 +26,6 @@ void MCELFObjectTargetWriter::sortRelocs(const MCAssembler &Asm, std::vector &Relocs) { } + +void MCELFObjectTargetWriter::addTargetSectionFlags(MCContext &Ctx, + MCSectionELF &Sec) {} diff --git a/lib/MC/MCObjectStreamer.cpp b/lib/MC/MCObjectStreamer.cpp index 4b6dad5ce8f..a622be6d24c 100644 --- a/lib/MC/MCObjectStreamer.cpp +++ b/lib/MC/MCObjectStreamer.cpp @@ -493,6 +493,12 @@ void MCObjectStreamer::EmitBytes(StringRef Data) { MCDataFragment *DF = getOrCreateDataFragment(); flushPendingLabels(DF, DF->getContents().size()); DF->getContents().append(Data.begin(), Data.end()); + + // EmitBytes might not cover all possible ways we emit data (or could be used + // to emit executable code in some cases), but is the best method we have + // right now for checking this. + MCSection *Sec = getCurrentSectionOnly(); + Sec->setHasData(true); } void MCObjectStreamer::EmitValueToAlignment(unsigned ByteAlignment, diff --git a/lib/MC/MCSection.cpp b/lib/MC/MCSection.cpp index 97bc65387dd..d4f11d10136 100644 --- a/lib/MC/MCSection.cpp +++ b/lib/MC/MCSection.cpp @@ -23,7 +23,8 @@ using namespace llvm; MCSection::MCSection(SectionVariant V, SectionKind K, MCSymbol *Begin) : Begin(Begin), BundleGroupBeforeFirstInst(false), HasInstructions(false), - IsRegistered(false), DummyFragment(this), Variant(V), Kind(K) {} + HasData(false), IsRegistered(false), DummyFragment(this), Variant(V), + Kind(K) {} MCSymbol *MCSection::getEndSymbol(MCContext &Ctx) { if (!End) diff --git a/lib/Target/ARM/ARMTargetObjectFile.cpp b/lib/Target/ARM/ARMTargetObjectFile.cpp index d0620761ea9..9c13359cba7 100644 --- a/lib/Target/ARM/ARMTargetObjectFile.cpp +++ b/lib/Target/ARM/ARMTargetObjectFile.cpp @@ -32,7 +32,8 @@ void ARMElfTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM) { const ARMBaseTargetMachine &ARM_TM = static_cast(TM); bool isAAPCS_ABI = ARM_TM.TargetABI == ARMBaseTargetMachine::ARMABI::ARM_ABI_AAPCS; - // genExecuteOnly = ARM_TM.getSubtargetImpl()->genExecuteOnly(); + bool genExecuteOnly = + ARM_TM.getMCSubtargetInfo()->hasFeature(ARM::FeatureExecuteOnly); TargetLoweringObjectFileELF::Initialize(Ctx, TM); InitializeELF(isAAPCS_ABI); @@ -40,6 +41,17 @@ void ARMElfTargetObjectFile::Initialize(MCContext &Ctx, if (isAAPCS_ABI) { LSDASection = nullptr; } + + // Make code section unreadable when in execute-only mode + if (genExecuteOnly) { + unsigned Type = ELF::SHT_PROGBITS; + unsigned Flags = + ELF::SHF_EXECINSTR | ELF::SHF_ALLOC | ELF::SHF_ARM_PURECODE; + // Since we cannot modify flags for an existing section, we create a new + // section with the right flags, and use 0 as the unique ID for + // execute-only text + TextSection = Ctx.getELFSection(".text", Type, Flags, 0, "", 0U); + } } const MCExpr *ARMElfTargetObjectFile::getTTypeGlobalReference( diff --git a/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp b/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp index 7d04c73fb3f..b8ba7584911 100644 --- a/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp +++ b/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp @@ -14,6 +14,7 @@ #include "llvm/MC/MCELFObjectWriter.h" #include "llvm/MC/MCExpr.h" #include "llvm/MC/MCFixup.h" +#include "llvm/MC/MCObjectFileInfo.h" #include "llvm/MC/MCObjectWriter.h" #include "llvm/MC/MCValue.h" #include "llvm/Support/ErrorHandling.h" @@ -40,6 +41,8 @@ namespace { bool needsRelocateWithSymbol(const MCSymbol &Sym, unsigned Type) const override; + + void addTargetSectionFlags(MCContext &Ctx, MCSectionELF &Sec) override; }; } // end anonymous namespace @@ -236,6 +239,21 @@ unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target, } } +void ARMELFObjectWriter::addTargetSectionFlags(MCContext &Ctx, + MCSectionELF &Sec) { + // The mix of execute-only and non-execute-only at link time is + // non-execute-only. To avoid the empty implicitly created .text + // section from making the whole .text section non-execute-only, we + // mark it execute-only if it is empty and there is at least one + // execute-only section in the object. + MCSectionELF *TextSection = + static_cast(Ctx.getObjectFileInfo()->getTextSection()); + if (Sec.getKind().isExecuteOnly() && !TextSection->hasInstructions() && + !TextSection->hasData()) { + TextSection->setFlags(TextSection->getFlags() | ELF::SHF_ARM_PURECODE); + } +} + std::unique_ptr llvm::createARMELFObjectWriter(uint8_t OSABI) { return llvm::make_unique(OSABI); diff --git a/test/CodeGen/ARM/execute-only.ll b/test/CodeGen/ARM/execute-only.ll index b5d9d89f1f7..3f42ca3b5f4 100644 --- a/test/CodeGen/ARM/execute-only.ll +++ b/test/CodeGen/ARM/execute-only.ll @@ -2,6 +2,9 @@ ; RUN: llc -mtriple=thumbv7m-eabi -mattr=+execute-only %s -o - | FileCheck --check-prefix=CHECK --check-prefix=CHECK-T2 %s ; RUN: llc -mtriple=thumbv8m.main-eabi -mattr=+execute-only %s -o - | FileCheck --check-prefix=CHECK --check-prefix=CHECK-T2 %s +; CHECK-NOT: {{^ *}}.text{{$}} +; CHECK: .section .text,"axy",%progbits,unique,0 + @var = global i32 0 define i32 @global() minsize { diff --git a/test/MC/ARM/elf-execute-only-section.ll b/test/MC/ARM/elf-execute-only-section.ll new file mode 100644 index 00000000000..2be3f4c7038 --- /dev/null +++ b/test/MC/ARM/elf-execute-only-section.ll @@ -0,0 +1,13 @@ +; RUN: llc < %s -mtriple=thumbv8m.base-eabi -mattr=+execute-only -filetype=obj %s -o - | \ +; RUN: llvm-readelf -s | FileCheck %s +; RUN: llc < %s -mtriple=thumbv8m.main-eabi -mattr=+execute-only -filetype=obj %s -o - | \ +; RUN: llvm-readelf -s | FileCheck %s +; RUN: llc < %s -mtriple=thumbv7m-eabi -mattr=+execute-only -filetype=obj %s -o - | \ +; RUN: llvm-readelf -s | FileCheck %s + +; CHECK-NOT: {{.text[ ]+PROGBITS[ ]+[0-9]+ [0-9]+ [0-9]+ [0-9]+ AX[^p]}} +; CHECK: {{.text[ ]+PROGBITS[ ]+[0-9]+ [0-9]+ [0-9]+ [0-9]+ AXp}} +define void @test_func() { +entry: + ret void +} diff --git a/test/MC/ELF/ARM/execute-only-populated-text-section.s b/test/MC/ELF/ARM/execute-only-populated-text-section.s new file mode 100644 index 00000000000..26a9c499f89 --- /dev/null +++ b/test/MC/ELF/ARM/execute-only-populated-text-section.s @@ -0,0 +1,27 @@ +// RUN: llvm-mc -filetype=obj -triple thumbv7m-arm-linux-gnu %s -o - \ +// RUN: | llvm-readobj -s -t | FileCheck %s + + .text + bx lr + + .section .text.foo,"axy" + bx lr + +// CHECK: Section { +// CHECK: Name: .text +// CHECK-NEXT: Type: SHT_PROGBITS (0x1) +// CHECK-NEXT: Flags [ (0x6) +// CHECK-NEXT: SHF_ALLOC (0x2) +// CHECK-NEXT: SHF_EXECINSTR (0x4) +// CHECK-NEXT: ] +// CHECK: } + +// CHECK: Section { +// CHECK: Name: .text.foo +// CHECK-NEXT: Type: SHT_PROGBITS (0x1) +// CHECK-NEXT: Flags [ (0x20000006) +// CHECK-NEXT: SHF_ALLOC (0x2) +// CHECK-NEXT: SHF_ARM_PURECODE (0x20000000) +// CHECK-NEXT: SHF_EXECINSTR (0x4) +// CHECK-NEXT: ] +// CHECK: } diff --git a/test/MC/ELF/ARM/execute-only-section.s b/test/MC/ELF/ARM/execute-only-section.s index 600ef5a41fd..524ba8ac687 100644 --- a/test/MC/ELF/ARM/execute-only-section.s +++ b/test/MC/ELF/ARM/execute-only-section.s @@ -20,8 +20,9 @@ foo: // CHECK: Section { // CHECK: Name: .text (16) // CHECK-NEXT: Type: SHT_PROGBITS (0x1) -// CHECK-NEXT: Flags [ (0x6) +// CHECK-NEXT: Flags [ (0x20000006) // CHECK-NEXT: SHF_ALLOC (0x2) +// CHECK-NEXT: SHF_ARM_PURECODE (0x20000000) // CHECK-NEXT: SHF_EXECINSTR (0x4) // CHECK-NEXT: ] // CHECK: Size: 0 diff --git a/test/MC/ELF/ARM/execute-only-text-section-data.s b/test/MC/ELF/ARM/execute-only-text-section-data.s new file mode 100644 index 00000000000..3e9abca34a2 --- /dev/null +++ b/test/MC/ELF/ARM/execute-only-text-section-data.s @@ -0,0 +1,27 @@ +// RUN: llvm-mc -filetype=obj -triple thumbv7m-arm-linux-gnu %s -o - \ +// RUN: | llvm-readobj -s -t | FileCheck %s + + .text + .ascii "test" + + .section .text.foo,"axy" + bx lr + +// CHECK: Section { +// CHECK: Name: .text +// CHECK-NEXT: Type: SHT_PROGBITS (0x1) +// CHECK-NEXT: Flags [ (0x6) +// CHECK-NEXT: SHF_ALLOC (0x2) +// CHECK-NEXT: SHF_EXECINSTR (0x4) +// CHECK-NEXT: ] +// CHECK: } + +// CHECK: Section { +// CHECK: Name: .text.foo +// CHECK-NEXT: Type: SHT_PROGBITS (0x1) +// CHECK-NEXT: Flags [ (0x20000006) +// CHECK-NEXT: SHF_ALLOC (0x2) +// CHECK-NEXT: SHF_ARM_PURECODE (0x20000000) +// CHECK-NEXT: SHF_EXECINSTR (0x4) +// CHECK-NEXT: ] +// CHECK: } -- cgit v1.2.3