[ELF] Minimal implementation for ARM static linking

The code is able to statically link the simplest case of:

  int main() { return 0; }

* Only works with ARM code - no Thumb code, no interwork (-marm -mno-thumb-interwork)
* musl libc built with no interwork and no Thumb code

Differential Revision: http://reviews.llvm.org/D6716

From: Denis Protivensky <dprotivensky@accesssoftek.com>
llvm-svn: 226643

lld/docs/open_projects.rst

@@ -8,6 +8,7 @@ Open Projects
 .. include:: ../lib/Driver/TODO.rst
 .. include:: ../lib/ReaderWriter/ELF/X86_64/TODO.rst
 .. include:: ../lib/ReaderWriter/ELF/AArch64/TODO.rst
+.. include:: ../lib/ReaderWriter/ELF/ARM/TODO.rst
 .. include:: ../tools/lld/TODO.txt
 
 Documentation TODOs

lld/lib/Driver/GnuLdDriver.cpp

@@ -192,6 +192,10 @@ getArchType(const llvm::Triple &triple, StringRef value) {
     if (value == "aarch64linux")
       return llvm::Triple::aarch64;
     return llvm::None;
+  case llvm::Triple::arm:
+    if (value == "armelf_linux_eabi")
+      return llvm::Triple::arm;
+    return llvm::None;
   default:
     return llvm::None;
   }

lld/lib/ReaderWriter/ELF/ARM/ARMELFFile.h

@@ -0,0 +1,41 @@
+//===--------- lib/ReaderWriter/ELF/ARM/ARMELFFile.h ----------------------===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_READER_WRITER_ELF_ARM_ARM_ELF_FILE_H
+#define LLD_READER_WRITER_ELF_ARM_ARM_ELF_FILE_H
+
+#include "ELFReader.h"
+
+namespace lld {
+namespace elf {
+
+class ARMLinkingContext;
+
+template <class ELFT> class ARMELFFile : public ELFFile<ELFT> {
+public:
+  ARMELFFile(std::unique_ptr<MemoryBuffer> mb, bool atomizeStrings)
+      : ELFFile<ELFT>(std::move(mb), atomizeStrings) {}
+
+  static ErrorOr<std::unique_ptr<ARMELFFile>>
+  create(std::unique_ptr<MemoryBuffer> mb, bool atomizeStrings) {
+    return std::unique_ptr<ARMELFFile<ELFT>>(
+        new ARMELFFile<ELFT>(std::move(mb), atomizeStrings));
+  }
+};
+
+template <class ELFT> class ARMDynamicFile : public DynamicFile<ELFT> {
+public:
+  ARMDynamicFile(const ARMLinkingContext &context, StringRef name)
+      : DynamicFile<ELFT>(context, name) {}
+};
+
+} // elf
+} // lld
+
+#endif // LLD_READER_WRITER_ELF_ARM_ARM_ELF_FILE_H

lld/lib/ReaderWriter/ELF/ARM/ARMELFReader.h

@@ -0,0 +1,60 @@
+//===--------- lib/ReaderWriter/ELF/ARM/ARMELFReader.h --------------------===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_READER_WRITER_ARM_ARM_ELF_READER_H
+#define LLD_READER_WRITER_ARM_ARM_ELF_READER_H
+
+#include "ARMELFFile.h"
+#include "ELFReader.h"
+
+namespace lld {
+namespace elf {
+
+typedef llvm::object::ELFType<llvm::support::little, 2, false> ARMELFType;
+
+struct ARMDynamicFileCreateELFTraits {
+  typedef llvm::ErrorOr<std::unique_ptr<lld::SharedLibraryFile>> result_type;
+
+  template <class ELFT>
+  static result_type create(std::unique_ptr<llvm::MemoryBuffer> mb,
+                            bool useUndefines) {
+    return lld::elf::ARMDynamicFile<ELFT>::create(std::move(mb), useUndefines);
+  }
+};
+
+struct ARMELFFileCreateELFTraits {
+  typedef llvm::ErrorOr<std::unique_ptr<lld::File>> result_type;
+
+  template <class ELFT>
+  static result_type create(std::unique_ptr<llvm::MemoryBuffer> mb,
+                            bool atomizeStrings) {
+    return lld::elf::ARMELFFile<ELFT>::create(std::move(mb), atomizeStrings);
+  }
+};
+
+class ARMELFObjectReader
+    : public ELFObjectReader<ARMELFType, ARMELFFileCreateELFTraits> {
+public:
+  ARMELFObjectReader(bool atomizeStrings)
+      : ELFObjectReader<ARMELFType, ARMELFFileCreateELFTraits>(
+            atomizeStrings, llvm::ELF::EM_ARM) {}
+};
+
+class ARMELFDSOReader
+    : public ELFDSOReader<ARMELFType, ARMDynamicFileCreateELFTraits> {
+public:
+  ARMELFDSOReader(bool useUndefines)
+      : ELFDSOReader<ARMELFType, ARMDynamicFileCreateELFTraits>(
+            useUndefines, llvm::ELF::EM_ARM) {}
+};
+
+} // namespace elf
+} // namespace lld
+
+#endif // LLD_READER_WRITER_ARM_ARM_ELF_READER_H

lld/lib/ReaderWriter/ELF/ARM/ARMExecutableWriter.h

@@ -0,0 +1,58 @@
+//===--------- lib/ReaderWriter/ELF/ARM/ARMExecutableWriter.h -------------===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLD_READER_WRITER_ELF_ARM_ARM_EXECUTABLE_WRITER_H
+#define LLD_READER_WRITER_ELF_ARM_ARM_EXECUTABLE_WRITER_H
+
+#include "ExecutableWriter.h"
+#include "ARMLinkingContext.h"
+
+namespace lld {
+namespace elf {
+
+template <class ELFT>
+class ARMExecutableWriter : public ExecutableWriter<ELFT> {
+public:
+  ARMExecutableWriter(ARMLinkingContext &context,
+                      ARMTargetLayout<ELFT> &layout);
+
+protected:
+  // Add any runtime files and their atoms to the output
+  bool createImplicitFiles(std::vector<std::unique_ptr<File>> &) override;
+
+  void finalizeDefaultAtomValues() override {
+    // Finalize the atom values that are part of the parent.
+    ExecutableWriter<ELFT>::finalizeDefaultAtomValues();
+  }
+
+  void addDefaultAtoms() override {
+    ExecutableWriter<ELFT>::addDefaultAtoms();
+  }
+
+private:
+  ARMLinkingContext &_context;
+  ARMTargetLayout<ELFT> &_armLayout;
+};
+
+template <class ELFT>
+ARMExecutableWriter<ELFT>::ARMExecutableWriter(ARMLinkingContext &context,
+                                               ARMTargetLayout<ELFT> &layout)
+    : ExecutableWriter<ELFT>(context, layout), _context(context),
+      _armLayout(layout) {}
+
+template <class ELFT>
+bool ARMExecutableWriter<ELFT>::createImplicitFiles(
+    std::vector<std::unique_ptr<File>> &result) {
+  ExecutableWriter<ELFT>::createImplicitFiles(result);
+  return true;
+}
+
+} // namespace elf
+} // namespace lld
+
+#endif // LLD_READER_WRITER_ELF_ARM_ARM_EXECUTABLE_WRITER_H

lld/lib/ReaderWriter/ELF/ARM/ARMLinkingContext.cpp

@@ -0,0 +1,21 @@
+//===--------- lib/ReaderWriter/ELF/ARM/ARMLinkingContext.cpp -------------===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ARMLinkingContext.h"
+#include "ARMRelocationPass.h"
+
+using namespace lld;
+using namespace lld::elf;
+
+void elf::ARMLinkingContext::addPasses(PassManager &pm) {
+  auto pass = createARMRelocationPass(*this);
+  if (pass)
+    pm.add(std::move(pass));
+  ELFLinkingContext::addPasses(pm);
+}

lld/lib/ReaderWriter/ELF/ARM/ARMLinkingContext.h

@@ -0,0 +1,40 @@
+//===--------- lib/ReaderWriter/ELF/ARM/ARMLinkingContext.h ---------------===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_READER_WRITER_ELF_ARM_ARM_LINKING_CONTEXT_H
+#define LLD_READER_WRITER_ELF_ARM_ARM_LINKING_CONTEXT_H
+
+#include "ARMTargetHandler.h"
+
+#include "lld/ReaderWriter/ELFLinkingContext.h"
+
+#include "llvm/Object/ELF.h"
+#include "llvm/Support/ELF.h"
+
+namespace lld {
+namespace elf {
+
+class ARMLinkingContext final : public ELFLinkingContext {
+public:
+  ARMLinkingContext(llvm::Triple triple)
+      : ELFLinkingContext(triple, std::unique_ptr<TargetHandlerBase>(
+                                      new ARMTargetHandler(*this))) {}
+
+  void addPasses(PassManager &) override;
+
+  uint64_t getBaseAddress() const override {
+    if (_baseAddress == 0)
+      return 0x400000;
+    return _baseAddress;
+  }
+};
+} // end namespace elf
+} // end namespace lld
+
+#endif

lld/lib/ReaderWriter/ELF/ARM/ARMRelocationHandler.cpp

@@ -0,0 +1,109 @@
+//===--------- lib/ReaderWriter/ELF/ARM/ARMRelocationHandler.cpp ----------===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ARMTargetHandler.h"
+#include "ARMLinkingContext.h"
+
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/MathExtras.h"
+
+using namespace lld;
+using namespace elf;
+
+static Reference::Addend readAddend_ARM_CALL(const uint8_t *location) {
+  const auto value = int32_t(
+      *reinterpret_cast<const llvm::support::little32_t *>(location));
+
+  const bool isBLX = (value & 0xF0000000) == 0xF0000000;
+  const int32_t bitH = isBLX ? ((value & 0x1000000) >> 24) : 0;
+
+  const int32_t result = ((value & 0xFFFFFF) << 2) | (bitH << 1);
+  return llvm::SignExtend64<26>(result);
+}
+
+static Reference::Addend readAddend(const uint8_t *location,
+                                    Reference::KindValue kindValue) {
+  switch (kindValue) {
+  case R_ARM_ABS32:
+    return int32_t(
+        *reinterpret_cast<const llvm::support::little32_t *>(location));
+  case R_ARM_CALL:
+    return readAddend_ARM_CALL(location);
+  default:
+    return 0;
+  }
+}
+
+static inline void applyArmReloc(uint8_t *location, uint32_t result,
+                                 uint32_t mask = 0xFFFFFFFF) {
+  assert(!(result & ~mask));
+  *reinterpret_cast<llvm::support::ulittle32_t *>(location) =
+      (uint32_t(*reinterpret_cast<llvm::support::ulittle32_t *>(location)) &
+       ~mask) | (result & mask);
+}
+
+/// \brief R_ARM_ABS32 - (S + A) | T => S + A
+static void relocR_ARM_ABS32(uint8_t *location, uint64_t P, uint64_t S,
+                             int64_t A) {
+  uint32_t result = (uint32_t)(S + A);
+  DEBUG_WITH_TYPE(
+      "ARM", llvm::dbgs() << "\t\tHandle " << LLVM_FUNCTION_NAME << " -";
+      llvm::dbgs() << " S: 0x" << Twine::utohexstr(S);
+      llvm::dbgs() << " A: 0x" << Twine::utohexstr(A);
+      llvm::dbgs() << " P: 0x" << Twine::utohexstr(P);
+      llvm::dbgs() << " result: 0x" << Twine::utohexstr(result) << "\n");
+  applyArmReloc(location, result);
+}
+
+/// \brief R_ARM_CALL - ((S + A) | T) - P => S + A - P
+static void relocR_ARM_CALL(uint8_t *location, uint64_t P, uint64_t S,
+                            int64_t A) {
+  uint32_t result = (uint32_t)((S + A) - P);
+  const uint32_t imm24 = (result & 0x03FFFFFC) >> 2;
+
+  DEBUG_WITH_TYPE(
+      "ARM", llvm::dbgs() << "\t\tHandle " << LLVM_FUNCTION_NAME << " -";
+      llvm::dbgs() << " S: 0x" << Twine::utohexstr(S);
+      llvm::dbgs() << " A: 0x" << Twine::utohexstr(A);
+      llvm::dbgs() << " P: 0x" << Twine::utohexstr(P);
+      llvm::dbgs() << " result: 0x" << Twine::utohexstr(result) << "\n");
+  applyArmReloc(location, imm24, 0xFFFFFF);
+}
+
+std::error_code ARMTargetRelocationHandler::applyRelocation(
+    ELFWriter &writer, llvm::FileOutputBuffer &buf, const lld::AtomLayout &atom,
+    const Reference &ref) const {
+  uint8_t *atomContent = buf.getBufferStart() + atom._fileOffset;
+  uint8_t *location = atomContent + ref.offsetInAtom();
+  uint64_t targetVAddress = writer.addressOfAtom(ref.target());
+  uint64_t relocVAddress = atom._virtualAddr + ref.offsetInAtom();
+
+  if (ref.kindNamespace() != Reference::KindNamespace::ELF)
+    return std::error_code();
+  assert(ref.kindArch() == Reference::KindArch::ARM);
+
+  // Calculate proper initial addend for the relocation
+  const Reference::Addend addend =
+      readAddend(location, ref.kindValue());
+
+  switch (ref.kindValue()) {
+  case R_ARM_NONE:
+    break;
+  case R_ARM_ABS32:
+    relocR_ARM_ABS32(location, relocVAddress, targetVAddress, addend);
+    break;
+  case R_ARM_CALL:
+    relocR_ARM_CALL(location, relocVAddress, targetVAddress, addend);
+    break;
+  default:
+    make_unhandled_reloc_error();
+  }
+
+  return std::error_code();
+}

lld/lib/ReaderWriter/ELF/ARM/ARMRelocationHandler.h

@@ -0,0 +1,32 @@
+//===--------- lib/ReaderWriter/ELF/ARM/ARMRelocationHandler.h ------------===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_READER_WRITER_ELF_ARM_ARM_RELOCATION_HANDLER_H
+#define LLD_READER_WRITER_ELF_ARM_ARM_RELOCATION_HANDLER_H
+
+#include "ARMTargetHandler.h"
+
+namespace lld {
+namespace elf {
+typedef llvm::object::ELFType<llvm::support::little, 2, false> ARMELFType;
+
+template <class ELFT> class ARMTargetLayout;
+
+class ARMTargetRelocationHandler final
+    : public TargetRelocationHandler {
+public:
+  std::error_code applyRelocation(ELFWriter &, llvm::FileOutputBuffer &,
+                                  const lld::AtomLayout &,
+                                  const Reference &) const override;
+};
+
+} // end namespace elf
+} // end namespace lld
+
+#endif // LLD_READER_WRITER_ELF_ARM_ARM_RELOCATION_HANDLER_H