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Rename pac_sign_lr and update reserved ranges. #4209

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Merged
merged 2 commits into from
Oct 12, 2022
Merged

Rename pac_sign_lr and update reserved ranges. #4209

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cac237d
Rename pac_sign_lr and update reserved ranges.
pmsjt Oct 11, 2022
eb36c0a
Merge branch 'main' into patch-1
colin-home Oct 12, 2022
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15 changes: 13 additions & 2 deletions docs/build/arm64-exception-handling.md
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Expand Up @@ -311,9 +311,20 @@ The unwind codes are encoded according to the table below. All unwind codes are
| | 11101000: Custom stack for `MSFT_OP_TRAP_FRAME` |
| | 11101001: Custom stack for `MSFT_OP_MACHINE_FRAME` |
| | 11101010: Custom stack for `MSFT_OP_CONTEXT` |
| | 11101011: Custom stack for `MSFT_OP_EC_CONTEXT` |
| | 11101100: Custom stack for `MSFT_OP_CLEAR_UNWOUND_TO_CALL` |
| | 1111xxxx: reserved |
| `pac_sign_return_address` | 11111100: sign the return address in `lr` with `pacibsp` |
| | 11101101: reserved |
| | 11101110: reserved |
| | 11101111: reserved |
| | 11110xxx: reserved |
| | 11111000'yyyyyyyy : reserved |
| | 11111001'yyyyyyyy'yyyyyyyy : reserved |
| | 11111010'yyyyyyyy'yyyyyyyy'yyyyyyyy : reserved |
| | 11111011'yyyyyyyy'yyyyyyyy'yyyyyyyy'yyyyyyyy : reserved |
| `pac_sign_lr` | 11111100: sign the return address in `lr` with `pacibsp` |
| | 11111101: reserved |
| | 11111110: reserved |
| | 11111111: reserved |

In instructions with large values covering multiple bytes, the most significant bits are stored first. This design makes it possible to find the total size in bytes of the unwind code by looking up only the first byte of the code. Since each unwind code is exactly mapped to an instruction in a prolog or epilog, you can compute the size of the prolog or epilog. Walk from the sequence start to the end, and use a lookup table or similar device to determine the length of the corresponding opcode.

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