# bddisasm x86/x64 instruction decoder

`no_std` Rust bindings for the [bddisasm](https://github.com/bitdefender/bddisasm) x86/x64 decoder library, built
on top of [bddisasm-sys](https://crates.io/crates/bddisasm-sys).

It supports all existing 16-bit, 32-bit and 64-bit instructions, offering a wide range of information about each one,
including:

- implicit operands
- explicit operands
- access mode for each operand
- CPUID feature flags
- CPU modes in which an instruction is valid

## Usage

Add `bddisasm` to your `Cargo.toml`:

```toml
[dependencies]
bddisasm = "0.4"
```

## Examples

### Decoding one instruction

Use [`DecodedInstruction::decode`](https://docs.rs/bddisasm/latest/bddisasm/decoded_instruction/struct.DecodedInstruction.html#method.decode)
to decode an instruction from a chunk of code.

```Rust
use bddisasm::{DecodedInstruction, DecodeMode, Mnemonic};

let code = vec![0x31, 0xc0];
match DecodedInstruction::decode(&code, DecodeMode::Bits32) {
    Ok(ins) => {
        assert_eq!(ins.mnemonic(), Mnemonic::XOR);
        println!("{}", ins);
    },
    Err(err) => println!("Unable to decode: {}", err),
}
```

### Decoding multiple instructions

Use [`Decoder`](https://docs.rs/bddisasm/latest/bddisasm/decoder/struct.Decoder.html) to decode multiple instructions
from a chunk of code.

```Rust
use bddisasm::{Decoder, DecodeMode};

let code = [
    // ENCLS
    0x0f, 0x01, 0xcf,
    // MOV       rax, qword ptr [rbx+rcx*4+0x1234]
    0x48, 0x8b, 0x84, 0x8b, 0x34, 0x12, 0x00, 0x00,
    // Not a valid instruction
    0x0f,
    // WRMSR
    0x0f, 0x30,
];
let decoder = Decoder::new(&code, DecodeMode::Bits64, 0x1234);

for ins in decoder {
    match ins {
        Ok(ins) => println!("{}", ins),
        Err(e) => println!("{}", e),
    }
}
```

This will print:

```text
ENCLS
MOV       rax, qword ptr [rbx+rcx*4+0x1234]
the provided input buffer is too small
WRMSR
```

Use [`Decoder::decode_next_with_info`](https://docs.rs/bddisasm/latest/bddisasm/decoder/struct.Decoder.html#method.decode_next_with_info)
to get information about the offset inside the code chunk at which an instruction was decoded from.

```Rust
use bddisasm::{Decoder, DecodeMode};

let code = [
    // ENCLS
    0x0f, 0x01, 0xcf,
    // MOV       rax, qword ptr [rbx+rcx*4+0x1234]
    0x48, 0x8b, 0x84, 0x8b, 0x34, 0x12, 0x00, 0x00,
    // Not a valid instruction
    0x0f,
    // WRMSR
    0x0f, 0x30,
];
let mut decoder = Decoder::new(&code, DecodeMode::Bits64, 0x1234);


// Keep decoding until there's nothing left to decode
while let Some((result, offset, _)) = decoder.decode_next_with_info() {
    match result {
        Ok(ins) => println!("{:#x} {}", offset, ins),
        Err(e) => println!("Error: `{}` at offset {:#x}", e, offset),
    }
}
```

This will print:

```text
0x0 ENCLS
0x3 MOV       rax, qword ptr [rbx+rcx*4+0x1234]
Error `the provided input buffer is too small` at offset 0xb
0xc WRMSR
```

### Working with instruction operands

Instruction operands can be analyzed using the [operand](https://docs.rs/bddisasm/latest/bddisasm/operand/index.html)
module. Rich informaion is offered for each type of operand. Bellow is a minimal example that looks at a memory operand.

```Rust
use bddisasm::{DecodedInstruction, DecodeMode, OpInfo};

// ` MOV       rax, qword ptr [rcx+r15*2]`
let code = b"\x4a\x8b\x04\x79";
let ins = DecodedInstruction::decode(code, DecodeMode::Bits64).unwrap();

// Get the operands
let operands = ins.operands();

// Get the second operand which is the source (`[rcx+r15*2]`)
let src = operands[1];

println!("Source operand type: {}", src.info);
match src.info {
    OpInfo::Mem(mem) => {
        if let Some(base) = mem.base {
            println!("Base register: {}", base);
        } else {
            println!("No base register");
        }

        if let Some(index) = mem.index {
            println!("Index register: {}", index);
        } else {
            println!("No index register");
        }

        if let Some(scale) = mem.scale {
            println!("Scale: {}", scale);
        } else {
            println!("No scale");
        }

        if let Some(displacement) = mem.disp {
            println!("Displacement: {}", displacement);
        } else {
            println!("No displacement");
        }
    },
    _ => unreachable!(),
}
```

Will print:

```text
Source operand type: memory
Base register: 1
Index register: 15
Scale: 2
No displacement
```

## Accessing the raw bindings

The raw `bddisasm_sys` bindings are available via the `ffi` re-export.

## Feature Flags

- `std` - adds a `std` dependency - the only visible difference when doing this is that [`DecodeError`] implements
the `Error` trait
