Ben Murdoch | 61f157c | 2016-09-16 13:49:30 +0100 | [diff] [blame] | 1 | // Copyright 2016 the V8 project authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style license that can be |
| 3 | // found in the LICENSE file. |
| 4 | |
| 5 | #include "src/eh-frame.h" |
| 6 | #include "src/objects-inl.h" |
| 7 | #include "src/objects.h" |
| 8 | |
| 9 | namespace v8 { |
| 10 | namespace internal { |
| 11 | |
| 12 | static const int DW_EH_PE_pcrel = 0x10; |
| 13 | static const int DW_EH_PE_datarel = 0x30; |
| 14 | static const int DW_EH_PE_udata4 = 0x03; |
| 15 | static const int DW_EH_PE_sdata4 = 0x0b; |
| 16 | |
| 17 | const int EhFrameHdr::kCIESize = 0; |
| 18 | |
| 19 | static const int kVersionSize = 1; |
| 20 | static const int kEncodingSpecifiersSize = 3; |
| 21 | |
| 22 | // |
| 23 | // In order to calculate offsets in the .eh_frame_hdr, we must know the layout |
| 24 | // of the DSO generated by perf inject, which is assumed to be the following: |
| 25 | // |
| 26 | // | ... | | |
| 27 | // +---------------+ <-- (F) --- | Larger offsets in file |
| 28 | // | | ^ | |
| 29 | // | Instructions | | .text v |
| 30 | // | | v |
| 31 | // +---------------+ <-- (E) --- |
| 32 | // |///////////////| |
| 33 | // |////Padding////| |
| 34 | // |///////////////| |
| 35 | // +---------------+ <-- (D) --- |
| 36 | // | | ^ |
| 37 | // | CIE | | |
| 38 | // | | | |
| 39 | // +---------------+ <-- (C) | .eh_frame |
| 40 | // | | | |
| 41 | // | FDE | | |
| 42 | // | | v |
| 43 | // +---------------+ <-- (B) --- |
| 44 | // | version | ^ |
| 45 | // +---------------+ | |
| 46 | // | encoding | | |
| 47 | // | specifiers | | |
| 48 | // +---------------+ <---(A) | .eh_frame_hdr |
| 49 | // | offset to | | |
| 50 | // | .eh_frame | | |
| 51 | // +---------------+ | |
| 52 | // | ... | ... |
| 53 | // |
| 54 | // (F) is aligned at a 16-byte boundary. |
| 55 | // (D) is aligned at a 8-byte boundary. |
| 56 | // (B) is aligned at a 4-byte boundary. |
| 57 | // (E), (C) and (A) have no alignment requirements. |
| 58 | // |
| 59 | // The distance between (A) and (B) is 4 bytes. |
| 60 | // |
| 61 | // The size of the .eh_frame is required to be a multiple of the pointer size, |
| 62 | // which means that (B) will be naturally aligned to a 4-byte boundary on all |
| 63 | // the architectures we support. |
| 64 | // |
| 65 | // Because (E) has no alignment requirements, there is padding between (E) and |
| 66 | // (D). (F) is aligned at a 16-byte boundary, thus to a 8-byte one as well. |
| 67 | // |
| 68 | EhFrameHdr::EhFrameHdr(Code* code) { |
| 69 | int code_size = code->is_crankshafted() ? code->safepoint_table_offset() |
| 70 | : code->instruction_size(); |
| 71 | version_ = 1; |
| 72 | eh_frame_ptr_encoding_ = DW_EH_PE_sdata4 | DW_EH_PE_pcrel; |
| 73 | lut_size_encoding_ = DW_EH_PE_udata4; |
| 74 | lut_entries_encoding_ = DW_EH_PE_sdata4 | DW_EH_PE_datarel; |
| 75 | |
| 76 | // .eh_frame pointer and LUT |
| 77 | if (code->has_unwinding_info()) { |
| 78 | DCHECK_GE(code->unwinding_info_size(), EhFrameHdr::kRecordSize); |
| 79 | int eh_frame_size = code->unwinding_info_size() - EhFrameHdr::kRecordSize; |
| 80 | |
| 81 | offset_to_eh_frame_ = |
| 82 | -(eh_frame_size + kVersionSize + kEncodingSpecifiersSize); // A -> D |
| 83 | lut_entries_number_ = 1; |
| 84 | offset_to_procedure_ = -(RoundUp(code_size, 8) + eh_frame_size); // B -> F |
| 85 | offset_to_fde_ = -(eh_frame_size - kCIESize); // B -> C |
| 86 | } else { |
| 87 | // Create a dummy table |
| 88 | offset_to_eh_frame_ = 0; |
| 89 | lut_entries_number_ = 0; |
| 90 | offset_to_procedure_ = 0; |
| 91 | offset_to_fde_ = 0; |
| 92 | } |
| 93 | } |
| 94 | |
| 95 | } // namespace internal |
| 96 | } // namespace v8 |