zjit

zjit is a bare-bones JIT code emitter for Zig wrapping GNU Lightning library. Supports x86_64, aarch64 and other architectures. Lightning manual and instruction set is available at https://www.gnu.org/software/lightning/manual/

Add to your project

zig fetch --save https://github.com/maxpoletaev/zjit.git

const zjit = b.dependency("zjit", .{
    .target = target,
    .optimize = optimize,
});
exe.root_module.addImport("zjit", zjit.module("root"));

Example

const zjit = @import("zjit");

const AddFunc = *const fn (i64, i64) callconv(.c) i64;

fn emitAddFunc(jit: zjit.State) AddFunc {
    jit.prolog();
    const r0 = zjit.R(0);
    const r1 = zjit.R(1);
    const a = jit.arg_l();
    const b = jit.arg_l();
    jit.getarg_l(r0, a);
    jit.getarg_l(r1, b);
    _ = jit.addr(r0, r0, r1);
    jit.retr(r0);
    jit.epilog();
    return @ptrCast(@alignCast(jit.emit()));
}

pub fn main() !void {
    zjit.init("myapp");
    defer zjit.deinit();

    const jit = zjit.State.init();
    defer jit.deinit();

    const add = emitAddFunc(jit);
    const result = add(3, 4);
    std.debug.print("{d}\n", .{result}); // 7
}

Quick Overview

Lightning exposes a portable RISC-like instruction set.

There are around 60 base instructions like add, mul, mov, etc., which come in different variants for different operand types.

• r - all operands are registers
• i - one operand is an immediate constant

All instructions are signed and use native word size by default, but there are additional suffixes to specify the operand size:

• _l — 64-bit integer
• _i — 32-bit integer
• _s — 16-bit integer
• _c — 8-bit integer
• _f — float
• _d — double
• _u — unsigned

Depending on the architecture, there are (at least) six general purpose registers: R(0-2) (caller-save), V(0-2) (callee-save), and six floating point registers: F(0-5).

Dynamic Linking

The library is built statically by default. For the sake of proper licensing: GNU Lightning is under LGPL, which means you may want to link to it dynamically. This can be changed via linkage option:

const zjit = b.dependency("zjit", .{
    .target = target,
    .optimize = optimize,
    .linkage = .dynamic,
});