vasm

Assembler API for the V programming language.

This library aims to provide the interface to generate native code out of a string

Features

• Compatible with rasm2 (from the radare2 project)
• Supports at least amd64 and arm64
• Statements separated by newlines or semicolons
• Support multiple architectures
• Limited instruction set supported
• Special syntax (not full-compliant with the spec)
• Aims to be used by the asm {} V statement for the C and Native backends
• Absolute and relative relocs
• Variables from V can be accessed by using the $ prefix
• Empty lines and comments // # are skipped

Example

This is an example on how to use the main program:

$ v run main.v mov eax, 33
b800000021

$ v run main.v test.amd64.asm
b8000000210f05cd8090ebfbb800000015

To target arm64 use the following flag:

$ v run main.v -arm64 test.arm64.asm

Using the API

module main

import vasm

fn main() {
    asmcode := '
        mov edi, %rc
        mov eax, %myvar
        syscall
        mov %res, eax
    '
    resolver := fn (varname string) &vasm.AsmLabel {
        return match varname {
            'myvar', 'rc', 'res' {
                &vasm.AsmLabel{
                    name: varname
                    off: 8
                }
            }
            else {
                &vasm.AsmLabel(0)
            }
        }
    }
    mut vcode := 'fn main() {
        myvar := \$if macos { 0x2000001 } \$else { 1 }
        rc := 42
        mut res := 0
        asm amd64 {
    '
    a := vasm.new_amd64(resolver)
    bb := a.assemble(asmcode) or { panic(err) }
    vcode += bb.to_cstring()
    println('$vcode
        }
        println(res)
    }
    ')
}

outputs:

$ v run example.v | v fmt - > a.v
$ cat a.v

fn main() {
    myvar := $if macos { 0x2000001 } $else { 1 }
    rc := 42
    mut res := 0
    asm amd64 {
        mov edi, rc
        mov eax, myvar
        syscall
        mov res, eax
        ; =r (res)
        ; r (rc)
          r (myvar)
    }
    println(res)
}

Runs like this:

$ v run a.v
$ echo $?
42