[sanitizer] Add Leb128 encoding/decoding

Reviewed By: dvyukov, kstoimenov

Differential Revision: https://reviews.llvm.org/D114464

compiler-rt/lib/sanitizer_common/CMakeLists.txt

@@ -148,6 +148,7 @@ set(SANITIZER_IMPL_HEADERS
   sanitizer_interceptors_ioctl_netbsd.inc
   sanitizer_interface_internal.h
   sanitizer_internal_defs.h
+  sanitizer_leb128.h
   sanitizer_lfstack.h
   sanitizer_libc.h
   sanitizer_libignore.h

compiler-rt/lib/sanitizer_common/sanitizer_leb128.h

@@ -0,0 +1,87 @@
+//===-- sanitizer_leb128.h --------------------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SANITIZER_LEB128_H
+#define SANITIZER_LEB128_H
+
+#include "sanitizer_common.h"
+#include "sanitizer_internal_defs.h"
+
+namespace __sanitizer {
+
+template <typename T, typename It>
+It EncodeSLEB128(T value, It begin, It end) {
+  bool more;
+  do {
+    u8 byte = value & 0x7f;
+    // NOTE: this assumes that this signed shift is an arithmetic right shift.
+    value >>= 7;
+    more = !((((value == 0) && ((byte & 0x40) == 0)) ||
+              ((value == -1) && ((byte & 0x40) != 0))));
+    if (more)
+      byte |= 0x80;
+    if (UNLIKELY(begin == end))
+      break;
+    *(begin++) = byte;
+  } while (more);
+  return begin;
+}
+
+template <typename T, typename It>
+It DecodeSLEB128(It begin, It end, T* v) {
+  T value = 0;
+  unsigned shift = 0;
+  u8 byte;
+  do {
+    if (UNLIKELY(begin == end))
+      return begin;
+    byte = *(begin++);
+    T slice = byte & 0x7f;
+    value |= slice << shift;
+    shift += 7;
+  } while (byte >= 128);
+  if (shift < 64 && (byte & 0x40))
+    value |= (-1ULL) << shift;
+  *v = value;
+  return begin;
+}
+
+template <typename T, typename It>
+It EncodeULEB128(T value, It begin, It end) {
+  do {
+    u8 byte = value & 0x7f;
+    value >>= 7;
+    if (value)
+      byte |= 0x80;
+    if (UNLIKELY(begin == end))
+      break;
+    *(begin++) = byte;
+  } while (value);
+  return begin;
+}
+
+template <typename T, typename It>
+It DecodeULEB128(It begin, It end, T* v) {
+  T value = 0;
+  unsigned shift = 0;
+  u8 byte;
+  do {
+    if (UNLIKELY(begin == end))
+      return begin;
+    byte = *(begin++);
+    T slice = byte & 0x7f;
+    value += slice << shift;
+    shift += 7;
+  } while (byte >= 128);
+  *v = value;
+  return begin;
+}
+
+}  // namespace __sanitizer
+
+#endif  // SANITIZER_LEB128_H

compiler-rt/lib/sanitizer_common/tests/CMakeLists.txt

@@ -23,6 +23,7 @@ set(SANITIZER_UNITTESTS
   sanitizer_format_interceptor_test.cpp
   sanitizer_hash_test.cpp
   sanitizer_ioctl_test.cpp
+  sanitizer_leb128_test.cpp
   sanitizer_libc_test.cpp
   sanitizer_linux_test.cpp
   sanitizer_list_test.cpp

compiler-rt/lib/sanitizer_common/tests/sanitizer_leb128_test.cpp

@@ -0,0 +1,83 @@
+//===-- sanitizer_leb128.cpp ------------------------------------*- C++ -*-===//
+//
+// 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 "sanitizer_common/sanitizer_leb128.h"
+
+#include <type_traits>
+
+#include "gtest/gtest.h"
+#include "sanitizer_common/sanitizer_common.h"
+#include "sanitizer_internal_defs.h"
+
+namespace __sanitizer {
+
+template <typename T>
+class Leb128Test : public ::testing::Test {};
+
+using Leb128TestTypes = ::testing::Types<u8, u16, u32, u64>;
+TYPED_TEST_SUITE(Leb128Test, Leb128TestTypes, );
+
+static uptr BitsNeeded(u64 v) {
+  if (!v)
+    return 1;
+  uptr r = 0;
+  uptr uptr_bits = 8 * sizeof(uptr);
+  while (v >> uptr_bits) {
+    r += uptr_bits;
+    v >>= uptr_bits;
+  }
+  return r + MostSignificantSetBitIndex(v) + 1;
+}
+
+TYPED_TEST(Leb128Test, SignedOverflow) {
+  using T = typename std::make_signed<TypeParam>::type;
+  u8 buffer[16] = {255};
+  T v = -128;
+  EXPECT_EQ(buffer + 1, EncodeSLEB128(v, buffer, buffer + 1));
+  EXPECT_EQ(buffer + 1, DecodeSLEB128(buffer, buffer + 1, &v));
+}
+
+TYPED_TEST(Leb128Test, Signed) {
+  using T = typename std::make_signed<TypeParam>::type;
+  T v = 0;
+  for (int i = 0; i < 100; ++i) {
+    u8 buffer[16] = {};
+    u8* p = EncodeSLEB128(v, std::begin(buffer), std::end(buffer));
+    EXPECT_EQ(int(BitsNeeded(v < 0 ? (-v - 1) : v) + 6 + 1) / 7, p - buffer)
+        << (int)v;
+    T v2;
+    u8* p2 = DecodeSLEB128(std::begin(buffer), std::end(buffer), &v2);
+    EXPECT_EQ(v, v2);
+    EXPECT_EQ(p, p2);
+    v = -TypeParam(v) * 3u + 1u;
+  }
+}
+
+TYPED_TEST(Leb128Test, UnsignedOverflow) {
+  using T = TypeParam;
+  u8 buffer[16] = {255};
+  T v = 255;
+  EXPECT_EQ(buffer + 1, EncodeULEB128(v, buffer, buffer + 1));
+  EXPECT_EQ(buffer + 1, DecodeULEB128(buffer, buffer + 1, &v));
+}
+
+TYPED_TEST(Leb128Test, Unsigned) {
+  using T = TypeParam;
+  T v = 0;
+  for (int i = 0; i < 100; ++i) {
+    u8 buffer[16] = {};
+    u8* p = EncodeULEB128(v, std::begin(buffer), std::end(buffer));
+    EXPECT_EQ(int(BitsNeeded(v) + 6) / 7, p - buffer);
+    T v2;
+    u8* p2 = DecodeULEB128(std::begin(buffer), std::end(buffer), &v2);
+    EXPECT_EQ(v, v2);
+    EXPECT_EQ(p, p2);
+    v = v * 3 + 1;
+  }
+}
+
+}  // namespace __sanitizer