jit

The x86-64 JIT backend of the aowljs JavaScript engine as a standalone nimony library, with no dependency on any JS value model: an assembler that emits position-independent bytes, W^X executable memory with fixed-signature calls into generated code, and linear-scan register assignment.

module
jit/x64asm	x86-64 assembler: Assembler, Reg, Xmm, Cond, Mem, Label; GPR, SSE2 and control-flow instructions appended to a seq[byte], rel32 label fixups resolved by finalize
jit/jitmem	JitMemory: copy code into fresh pages, flip them read-execute (never W+X); jitCall0..4, jitCallF1/F2 to call it, procAddr / loadFnPtr / ptrToInt for runtime helpers
jit/linscan	linearScan (GPR + xmm pools, spill slots, weight-per-lifetime eviction, two-address hints), loopDepths, depthWeight
jit	re-exports all three

Generated code is an ordinary C-ABI function (SysV on Linux, Win64 on Windows); argRegs and shadowSpace pick the right convention at compile time. Absolute addresses are embedded with mov r, imm64 + call r, so code needs no relocation after install.

Usage

import jit

var a = initAssembler()
let done = a.newLabel()
a.movImm(rax, 0)              # sumTo(n) = 1 + ... + n
a.mov(rcx, argRegs[0])
a.test(rcx, rcx)
a.jcc(cLessEq, done)
let top = a.hereLabel()
a.add(rax, rcx)
a.decr(rcx)
a.jcc(cNotEqual, top)
a.bindLabel(done)
a.ret()
doAssert a.finalize()          # false if a referenced label was never bound

var jm = initJitMemory()
let f = jm.install(a.buf)      # nil if pages could not be mapped/protected
echo jitCall1(f, 10)           # 55
jm.release()                   # unmaps everything installed from jm

Register locations from linearScan: 0..15 a GPR, 100 + n xmm n, -(k+1) spill slot k. loc must be presized to the value count and vals sorted by start.

Users

• aowljs-engine: the baseline JIT and the optimizing tier (opt.nim) are built on these three modules. The engine's build finds this checkout via AOWL_JIT (default ../jit), like AOWL_REGEX / AOWL_UNICODE, and imports jit/x64asm etc.
• aowli (the nimony interpreter/runtime) has no assembler or executable-memory code of its own; its native FFI (hostdyn.nim) classifies SysV argument registers but calls through C. The API here is engine-neutral, so aowli can adopt it as-is if it grows a JIT.

Test

nimony c -p:src tests/test_jit.nim   # then run the binary (x86-64 only)

License

MIT. The assembler is modelled on Bali's amd64 assembler (BSD-3-Clause, Trayambak Rai), itself derived from catnip's x64assembler (MIT, RSDuck); see the header of src/jit/x64asm.nim.