1/*
2 * Copyright (C) 2015 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#include "linker/x86/relative_patcher_x86.h"
18
19#include "compiled_method.h"
20
21namespace art {
22namespace linker {
23
24void X86RelativePatcher::PatchDexCacheReference(std::vector<uint8_t>* code,
25                                                const LinkerPatch& patch,
26                                                uint32_t patch_offset,
27                                                uint32_t target_offset) {
28  uint32_t anchor_literal_offset = patch.PcInsnOffset();
29  uint32_t literal_offset = patch.LiteralOffset();
30
31  // Check that the anchor points to pop in a "call +0; pop <reg>" sequence.
32  DCHECK_GE(anchor_literal_offset, 5u);
33  DCHECK_LT(anchor_literal_offset, code->size());
34  DCHECK_EQ((*code)[anchor_literal_offset - 5u], 0xe8u);
35  DCHECK_EQ((*code)[anchor_literal_offset - 4u], 0x00u);
36  DCHECK_EQ((*code)[anchor_literal_offset - 3u], 0x00u);
37  DCHECK_EQ((*code)[anchor_literal_offset - 2u], 0x00u);
38  DCHECK_EQ((*code)[anchor_literal_offset - 1u], 0x00u);
39  DCHECK_EQ((*code)[anchor_literal_offset] & 0xf8u, 0x58u);
40
41  // Check that the patched data contains kDummy32BitOffset.
42  constexpr int kDummy32BitOffset = 256;  // Must match X86Mir2Lir::kDummy32BitOffset.
43  DCHECK_LE(literal_offset, code->size());
44  DCHECK_EQ((*code)[literal_offset + 0u], static_cast<uint8_t>(kDummy32BitOffset >> 0));
45  DCHECK_EQ((*code)[literal_offset + 1u], static_cast<uint8_t>(kDummy32BitOffset >> 8));
46  DCHECK_EQ((*code)[literal_offset + 2u], static_cast<uint8_t>(kDummy32BitOffset >> 16));
47  DCHECK_EQ((*code)[literal_offset + 3u], static_cast<uint8_t>(kDummy32BitOffset >> 24));
48
49  // Apply patch.
50  uint32_t anchor_offset = patch_offset - literal_offset + anchor_literal_offset;
51  uint32_t diff = target_offset - anchor_offset;
52  (*code)[literal_offset + 0u] = static_cast<uint8_t>(diff >> 0);
53  (*code)[literal_offset + 1u] = static_cast<uint8_t>(diff >> 8);
54  (*code)[literal_offset + 2u] = static_cast<uint8_t>(diff >> 16);
55  (*code)[literal_offset + 3u] = static_cast<uint8_t>(diff >> 24);
56}
57
58}  // namespace linker
59}  // namespace art
60