ed53b4a54d
It is possible to configure the build process such that decoding of 32 bit and 64 bit instructions can be chosen at runtime using an additional parameter of the decode function. The header file is now entirely architecture-independent and no longer required any previous defines. Decoding x86-64 still requires a 64-bit pointer size.
18 lines
1.7 KiB
Markdown
18 lines
1.7 KiB
Markdown
# libx86decode
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A fast and lightweight decoder for x86 and x86-64. *This is not a disassembler, it does not intend to produce valid assembly.* To meet the goal of speed, lookup tables are used to map the opcode the (internal) description of the instruction encoding. This table currently has a size of roughly 21 kiB.
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### Known issues
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- An implicit `FWAIT` in FPU instructions is decoded as a separate instruction. For example, the instruction `FINIT` is decoded as an `FWAIT` followed by an `FINIT` where as `FNINIT` is decoded as a plain `FINIT` instruction.
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- The AVX VSIB encoding is not supported yet, all instructions using this will result in a decode error.
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- A mandatory L0 or L1 in the VEX prefix is currently ignored to reduce the size of the prefix tables. The only instructions where this has an effect are `VZEROALL` (L1) and `VZEROUPPER` (L0) and are currently decoded as `VZERO`, the vector length prefix can be used to determine the actual instruction.
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- The EVEX prefix (AVX-512) is not supported (yet).
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- No ABI stability as the value associated with the mnemonics will change if further instructions are added. When using this library, please link it statically.
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- The instruction formatter does not include prefixes. (Help needed.)
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- The layout of entries in the tables can be improved to improve usage of caches. (Help needed.)
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- Low test coverage. (Help needed.)
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- No benchmarking has been performed yet. (Help needed.)
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- Prefixes for indirect jumps and calls are not properly decoded, e.g. `notrack`, `bnd`. This requires additional information on the prefix ordering, which is currently not decoded. (Analysis of performance impact and help needed.)
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If you find any other issues, please report a bug. Or, even better, send a patch fixing the issue.
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