1 files changed, 140 insertions, 0 deletions
diff --git a/lld/MachO/EhFrame.cpp b/lld/MachO/EhFrame.cpp
new file mode 100644
index 000000000000..50d8accc0596
--- /dev/null
+++ b/lld/MachO/EhFrame.cpp
@@ -0,0 +1,140 @@
+//===- EhFrame.cpp --------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "EhFrame.h"
+#include "InputFiles.h"
+
+#include "lld/Common/ErrorHandler.h"
+#include "llvm/BinaryFormat/Dwarf.h"
+#include "llvm/Support/Endian.h"
+
+using namespace llvm;
+using namespace lld;
+using namespace lld::macho;
+using namespace llvm::support::endian;
+
+uint64_t EhReader::readLength(size_t *off) const {
+  const size_t errOff = *off;
+  if (*off + 4 > data.size())
+    failOn(errOff, "CIE/FDE too small");
+  uint64_t len = read32le(data.data() + *off);
+  *off += 4;
+  if (len == dwarf::DW_LENGTH_DWARF64) {
+    // FIXME: test this DWARF64 code path
+    if (*off + 8 > data.size())
+      failOn(errOff, "CIE/FDE too small");
+    len = read64le(data.data() + *off);
+    *off += 8;
+  }
+  if (*off + len > data.size())
+    failOn(errOff, "CIE/FDE extends past the end of the section");
+  return len;
+}
+
+void EhReader::skipValidLength(size_t *off) const {
+  uint32_t len = read32le(data.data() + *off);
+  *off += 4;
+  if (len == dwarf::DW_LENGTH_DWARF64)
+    *off += 8;
+}
+
+// Read a byte and advance off by one byte.
+uint8_t EhReader::readByte(size_t *off) const {
+  if (*off + 1 > data.size())
+    failOn(*off, "unexpected end of CIE/FDE");
+  return data[(*off)++];
+}
+
+uint32_t EhReader::readU32(size_t *off) const {
+  if (*off + 4 > data.size())
+    failOn(*off, "unexpected end of CIE/FDE");
+  uint32_t v = read32le(data.data() + *off);
+  *off += 4;
+  return v;
+}
+
+uint64_t EhReader::readPointer(size_t *off) const {
+  if (*off + wordSize > data.size())
+    failOn(*off, "unexpected end of CIE/FDE");
+  uint64_t v;
+  if (wordSize == 8)
+    v = read64le(data.data() + *off);
+  else {
+    assert(wordSize == 4);
+    v = read32le(data.data() + *off);
+  }
+  *off += wordSize;
+  return v;
+}
+
+// Read a null-terminated string.
+StringRef EhReader::readString(size_t *off) const {
+  if (*off > data.size())
+    failOn(*off, "corrupted CIE (failed to read string)");
+  const size_t maxlen = data.size() - *off;
+  auto *c = reinterpret_cast<const char *>(data.data() + *off);
+  size_t len = strnlen(c, maxlen);
+  if (len == maxlen) // we failed to find the null terminator
+    failOn(*off, "corrupted CIE (failed to read string)");
+  *off += len + 1; // skip the null byte too
+  return StringRef(c, len);
+}
+
+void EhReader::skipLeb128(size_t *off) const {
+  const size_t errOff = *off;
+  while (*off < data.size()) {
+    uint8_t val = data[(*off)++];
+    if ((val & 0x80) == 0)
+      return;
+  }
+  failOn(errOff, "corrupted CIE (failed to read LEB128)");
+}
+
+void EhReader::failOn(size_t errOff, const Twine &msg) const {
+  fatal(toString(file) + ":(__eh_frame+0x" +
+        Twine::utohexstr(dataOff + errOff) + "): " + msg);
+}
+
+/*
+ * Create a pair of relocs to write the value of:
+ *   `b - (offset + a)` if Invert == false
+ *   `(a + offset) - b` if Invert == true
+ */
+template <bool Invert = false>
+static void createSubtraction(PointerUnion<Symbol *, InputSection *> a,
+                              PointerUnion<Symbol *, InputSection *> b,
+                              uint64_t off, uint8_t length,
+                              SmallVectorImpl<Reloc> *newRelocs) {
+  auto subtrahend = a;
+  auto minuend = b;
+  if (Invert)
+    std::swap(subtrahend, minuend);
+  assert(subtrahend.is<Symbol *>());
+  Reloc subtrahendReloc(target->subtractorRelocType, /*pcrel=*/false, length,
+                        off, /*addend=*/0, subtrahend);
+  Reloc minuendReloc(target->unsignedRelocType, /*pcrel=*/false, length, off,
+                     (Invert ? 1 : -1) * off, minuend);
+  newRelocs->push_back(subtrahendReloc);
+  newRelocs->push_back(minuendReloc);
+}
+
+void EhRelocator::makePcRel(uint64_t off,
+                            PointerUnion<Symbol *, InputSection *> target,
+                            uint8_t length) {
+  createSubtraction(isec->symbols[0], target, off, length, &newRelocs);
+}
+
+void EhRelocator::makeNegativePcRel(
+    uint64_t off, PointerUnion<Symbol *, InputSection *> target,
+    uint8_t length) {
+  createSubtraction</*Invert=*/true>(isec, target, off, length, &newRelocs);
+}
+
+void EhRelocator::commit() {
+  isec->relocs.insert(isec->relocs.end(), newRelocs.begin(), newRelocs.end());
+}