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Alexis Engelke
2019-02-24 17:13:49 +01:00
parent b105c48903
commit f4644430b8
1 changed files with 7 additions and 6 deletions
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README.md
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@@ -4,17 +4,18 @@ Fadec is a fast and lightweight decoder for x86-32 and x86-64. To meet the goal
*Note: This is not a disassembler, it does not intend to produce valid assembly.* *Note: This is not a disassembler, it does not intend to produce valid assembly.*
### Key features ## Key features
**Q: Why not just just use any other decoder available out there?** > **Q: Why not just just use any other decoder available out there?**
A: Because I needed to embed a small and fast decoder in a project which didn't link against a libc. >
> A: Because I needed to embed a small and fast decoder in a project which didn't link against a libc.
- **Small size:** the compiled library uses only 40 kiB and the main decode routine is only a few hundreds lines of code. - **Small size:** the compiled library uses only 40 kiB and the main decode routine is only a few hundreds lines of code.
- **Performance:** Fadec is significantly times faster than libopcodes or Capstone due to the absence of high-level abstractions and the small lookup table. - **Performance:** Fadec is significantly times faster than libopcodes or Capstone due to the absence of high-level abstractions and the small lookup table.
- **Almost no dependencies:** the formatter only uses the function `snprintf`, the decoder itself has no dependencies, making it suitable for environments without a full libc or `malloc`-style memory allocation. - **Almost no dependencies:** the formatter only uses the function `snprintf`, the decoder itself has no dependencies, making it suitable for environments without a full libc or `malloc`-style memory allocation.
- **Correctness:** even corner cases should be handled correctly (if not, that's a bug), e.g., the order of prefixes, the presence of the `lock` prefix, or properly handling VEX.W in 32-bit mode. - **Correctness:** even corner cases should be handled correctly (if not, that's a bug), e.g., the order of prefixes, the presence of the `lock` prefix, or properly handling VEX.W in 32-bit mode.
### Basic Usage ## Basic Usage
```c ```c
FdInstr instr; FdInstr instr;
// Decode from buffer in 64-bit mode and virtual address 0x401000 // Decode from buffer in 64-bit mode and virtual address 0x401000
@@ -23,7 +24,7 @@ int ret = fd_decode(buffer, sizeof(buffer), 64, 0x401000, &instr);
// Relevant properties of instructions can now be queries using the FD_* macros. // Relevant properties of instructions can now be queries using the FD_* macros.
``` ```
### Intended differences ## Intended differences to other decoders
To achieve higher performance, minor differences to other decoders exist, requiring special handling. To achieve higher performance, minor differences to other decoders exist, requiring special handling.
- The registers `ah`/... and `spl`/... have the same number (as in machine code). Distinguishing them is possible using `FD_OP_REG_HIGH`. - The registers `ah`/... and `spl`/... have the same number (as in machine code). Distinguishing them is possible using `FD_OP_REG_HIGH`.
@@ -38,7 +39,7 @@ To achieve higher performance, minor differences to other decoders exist, requir
- The instructions `bsf`/`tzcnt` and `bsr`/`lzcnt` can only be distinguished by the presence of a `rep` prefix (matching the machine code encoding). Note that on older processors `tzcnt`/`lzcnt` are executed as plain `rep bsf`/`rep bsr`. - The instructions `bsf`/`tzcnt` and `bsr`/`lzcnt` can only be distinguished by the presence of a `rep` prefix (matching the machine code encoding). Note that on older processors `tzcnt`/`lzcnt` are executed as plain `rep bsf`/`rep bsr`.
- The instructions `movbe`/`crc32` can only be distinguished by the presence of a `repnz` prefix. - The instructions `movbe`/`crc32` can only be distinguished by the presence of a `repnz` prefix.
### Known issues ## Known issues
- MMX instructions are not supported yet. - MMX instructions are not supported yet.
- The AVX VSIB encoding is not supported yet, all instructions using this will result in a decode error. - The AVX VSIB encoding is not supported yet, all instructions using this will result in a decode error.
- The EVEX prefix (AVX-512) is not supported (yet). - The EVEX prefix (AVX-512) is not supported (yet).