[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

1 files changed, 109 insertions, 0 deletions

diff --git a/lld/lib/ReaderWriter/ELF/ARM/ARMRelocationHandler.cpp b/lld/lib/ReaderWriter/ELF/ARM/ARMRelocationHandler.cpp
new file mode 100644
index 00000000000..e3e1d837ca1
--- /dev/null
+++ b/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();
+}