Kasm
Kasm is a runtime assembler library for Kotlin. It allows to assemble and execute machine code at runtime.
Features
- x86-64 up to AVX2
- Allows save code execution, handling segmentation faults and zero divisions etc.
- Support for automatic CPU feature detection (see
CpuId) - Contains a Kotlin DSL (see
Assembler) - Supports disassembling (through Capstone)
- Full control over encoding (see
EncodingOptions):- Encode with or without SIB (if possible)
- Force REX prefix
- Use long or short VEX prefix
- Set unused bits in Mod.RM/REX/VEX
- Legacy prefix order
Installation
$ git clone --recursive https://github.com/evoasm/kasm
The project does currently come without any build files. It is recommended that you import the project into IntelliJ IDEA.
Requirements
- Kotlin/JVM
- Capstone for disassembling (optional).
- POSIX-compliant OS (Linux and Mac OS X should both work).
- CMake (see below, optional)
If you want support for code execution and disassembling (through Capstone) you must build the corresponding native modules
$ cd kasm-native/lib
$ mkdir build
$ cd build
$ cmake ..
Shared libraries are output to kasm-native/lib. If you get a UnsatisfiedLinkError exception add -Djava.library.path=../kasm-native/lib to your VM options.
Examples
Assembler
val buffer = NativeBuffer(1024)
Assembler(buffer).emitStackFrame {
mov(RBX, 0)
mov(RAX, 0)
divRdxRax(RBX)
}
buffer.execute() // will throw kasm.ZeroDivisionException
Assembler(buffer).emitStackFrame {
mov(RBX, AddressExpression(0x0))
}
buffer.execute() // will throw kasm.SegmentationFaultException
Instruction
val buffer = NativeBuffer(1024)
// add eax, [ebx]
AddR32Rm32.encode(buffer, EAX, AddressExpression32(EBX))
// add [ebx], eax
AddRmR32.encode(buffer, AddressExpression32(EBX), EAX)
CpuId
println(CpuId.features) // [SEP, CLFSH, DS, ACPI, SSE, SSE2, SS, ...
EncodingOptions
AddRm32Imm32.encode(buffer, EAX, 0x10, options = EncodingOptions(rexX = 0x0, forceRex = true))
println(buffer.toByteString()) //40 81 C0 10 00 00 00
AddRm32Imm32.encode(buffer, EAX, 0x10, options = EncodingOptions(rexX = 0x1, forceRex = true))
println(buffer.toByteString()) //42 81 C0 10 00 00 00
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