forked from OSchip/llvm-project
55f1fbf005
Currently, when llvm-objdump is disassembling a code section and encounters a point where no instruction can be decoded, it uses the same policy on all targets: consume one byte of the section, emit it as "<unknown>", and try disassembling from the next byte position. On an architecture where instructions are always 4 bytes long and 4-byte aligned, this makes no sense at all. If a 4-byte word cannot be decoded as an instruction, then the next place that a valid instruction could //possibly// be found is 4 bytes further on. Disassembling from a misaligned address can't possibly produce anything that the code generator intended, or that the CPU would even attempt to execute. This patch introduces a new MCDisassembler virtual method called `suggestBytesToSkip`, which allows each target to choose its own resynchronization policy. For Arm (as opposed to Thumb) and AArch64, I've filled in the new method to return a fixed width of 4. Thumb is a more interesting case, because the criterion for identifying 2-byte and 4-byte instruction encodings is very simple, and doesn't require the particular instruction to be recognized. So `suggestBytesToSkip` is also passed an ArrayRef of the bytes in question, so that it can take that into account. The new test case shows Thumb disassembly skipping over two unrecognized instructions, and identifying one as 2-byte and one as 4-byte. For targets other than Arm and AArch64, this is NFC: the base class implementation of `suggestBytesToSkip` still returns 1, so that the existing behavior is unchanged. Other targets can fill in their own implementations as they see fit; I haven't attempted to choose a new behavior for each one myself. I've updated all the call sites of `MCDisassembler::getInstruction` in llvm-objdump, and also one in sancov, which was the only other place I spotted the same idiom of `if (Size == 0) Size = 1` after a call to `getInstruction`. Reviewed By: DavidSpickett Differential Revision: https://reviews.llvm.org/D130357 |
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| .. | ||
| CMakeLists.txt | ||
| Disassembler.cpp | ||
| Disassembler.h | ||
| MCDisassembler.cpp | ||
| MCExternalSymbolizer.cpp | ||
| MCRelocationInfo.cpp | ||
| MCSymbolizer.cpp | ||