RubyKaigi2026: Invariants in my own Ruby

RubyKaigi2026 presentation slides.

Transcript

1. Invariants in my own Ruby: some things must never change monochrome (Soichiro Isshiki)
2. About me - monochrome (@s_isshiki1969) or 一色聡一郎 - surgeon - loves Ruby, Rust and assembly - developing monoruby
3. monoruby - https://github.com/sisshiki1969/monoruby - Yet another Ruby implementation with JIT compiler - Written in Rust from (almost) scratch - No runtime dependency on LLVM, JVM, .. - Includes parser, garbage collector, interpreter - Only x86-64 / Linux is supported - new! Supports RubyGems and Bundler - new! Trying to run ruby/spec
4. RubyKaigi2024
5. JIT code transition execution trace deoptimize bytecode interpreter JIT compiler
6. frames per sec Optcarrot benchmark fps history (up to 3000 frames)
7. RubyKaigi2025
8. compile at one time Specialization “specialized” Array#each 1000.times do |i| puts i end do |i| puts i end class Array def each .. yield .. end end
9. benchmark: specialization
10. Compatibility: ruby/spec Metric Value Examples 22,309 Passed 12,813 Failed 3,976 Errors 5,568 Overall pass rate 57.4% Categories at 100% 10
11. ruby-bench
12. Integer#+
13. 0xa0 %dst %lhs %rhs ClassId(lhs) ClassId(rhs) 8 bytes 8 bytes ADD instruction opcode operand %7 = %2 + %3 [Integer][Integer] inline cache
14. Store Overflow Guard Add Fixnum Guard for rhs Fixnum Guard for lhs Load lhs & rhs %7 = %2 + %3 [Integer][Integer] mov rdi,QWORD PTR [rbp-0x40] mov rsi,r15 test rdi,0x1 je $deoptimize test rsi,0x1 je $deoptimize sub rdi,0x1 add rdi,rsi jo $deoptimize mov r15,rdi asm code for ADD
15. Store Overflow Guard Add Fixnum Guard for rhs Fixnum Guard for lhs Load lhs & rhs %2 = 1 %3 = 2 %7 = %2 + %3 [Integer][Integer] mov rdi,QWORD PTR [rbp-0x40] mov rsi,r15 test rdi,0x1 je 0xffeaf02 test rsi,0x1 je 0xffeaf3b sub rdi,0x1 add rdi,rsi jo 0xffeaf43 mov r15,rdi asm code for ADD
16. Store %2 = 1 %3 = 2 %7 = %2 + %3 [Integer][Integer] mov r15,0x7 constant folding
17. METHOD_CALL instruction opcode inline cache 0x1e %dst CallsiteId cached FuncId 0x82 %rcv %args pos cached ClassId cached version opcode operand %3 = %0.f(%3) [#<main>] FuncId(1849)
18. Push frame Set arguments Class Version Guard Call Check Exception Check Stack Overflow Pop frame %2 = %0.f(%2) mov eax,DWORD PTR [rip+$GlobalVersion] cmp eax,DWORD PTR [rip+$ICVersion] jne $deoptimize cmp rsp,QWORD PTR [rbx+0x18] jle 0xfff3461 cmp DWORD PTR [rip+$GCCounter],0x8 jge 0xfff3489 mov rax,QWORD PTR [r14-0x18] mov QWORD PTR [rsp-0x40],rax mov QWORD PTR [rsp-0x48],r15 sub rsp,0x20 xor rax,rax push rax movabs rax,0x10000005000007b2 push rax xor rax,rax push rax add rsp,0x38 lea r14,[rsp-0x28] mov QWORD PTR [rsp-0x20],r14 mov rdi,QWORD PTR [rbx] lea rsi,[rsp-0x18] mov QWORD PTR [rsi],rdi mov QWORD PTR [rbx],rsi call $JIT_f_entry lea r14,[rbp-0x8] mov QWORD PTR [rbx],r14 mov r14,QWORD PTR [rbp-0x10] test rax,rax je 0xfff3266 mov r15,rax cost of method call in Ruby
19. specializing + constant folding a = 1 b = 2 c = f(a, b) f(1, 2) = 3 def f(a, b) a + b end
20. Store Version Guard specializing + constant folding %2 = 1 %3 = 2 %7 = %2 %8 = %3 %7 = %0.f(%7,%8) [#<main>] FuncId(2835) mov eax,DWORD PTR [rip+$GlobalVersion] cmp eax,DWORD PTR [rip+$ICVersion] jne $deoptimize mov r15,0x7
21. really?
22. a = 1 b = 2 class Integer def +(other) 42 end end p a + b sample0.rb There are no assignments to local variables a and b.
23. a = 1 b = 2 class Integer def +(other) 42 end end p a + b sample0.rb There are no assignments to local variable a and b. ❯ monoruby sample0.rb 42
24. a = 1 b = 2 class Integer def +(other) 42 end end p a + b sample0.rb Redefinition of basic ops: 1+2=3 isn’t an eternal truth. ❯ monoruby sample0.rb 42
25. sample1.rb alias evil eval curse = "a = 40" a = 1 b = 2 evil(curse) p a + b
26. sample1.rb alias evil eval curse = "a = 40" a = 1 b = 2 evil(curse) p a + b ❯ monoruby sample1.rb 42
27. sample1.rb alias evil eval curse = "a = 40" a = 1 b = 2 evil(curse) p a + b Eval: eval can do evil things.
28. sample2.rb $b = binding a = 1 b = 2 evil p a + b def evil 　$b.eval("a = 40") end Compiler knows evil is not Kernel.#eval. and there are no method definitions inside it.
29. sample2.rb $b = binding a = 1 b = 2 evil p a + b def evil $b.eval("a = 40") end ❯ monoruby sample2.rb 42 Compiler knows evil is not Kernel.#eval. and there are no method definitions inside it.
30. sample2.rb alias evil eval curse = "a = 40" a = 1 b = 2 evil(curse) $b = binding a = 1 b = 2 evil p a + b def evil $b.eval("a = 40") end Binding: Local variables are not local.
31. sample3.rb alias evil eval curse = "a = 40" a = 1 b = 2 evil(curse) p(a + b) tp = TracePoint.new(:line) do |tp| if tp.lineno == 8 tp.binding.eval("a = 40") end end tp.enable a = 1 b = 2 p a + b ❯ monoruby sample3.rb 42
32. sample3.rb alias evil eval curse = "a = 40" a = 1 b = 2 evil(curse) p(a + b) tp = TracePoint.new(:line) do |tp| if tp.lineno == 8 tp.binding.eval("a = 40") end end tp.enable a = 1 b = 2 p a + b TracePoint: You can do everything anywhere.
33. How do we fight against these devils in Ruby? - Redefinition of basic methods - Eval - Binding - TracePoint
34. How do we fight against these devils in Ruby? Invariants - if some assumptions are broken, we must immediately escape from JIT code, and bail out to the interpreter. - version in inline cache - receiver’s class in inline cache - constants - the local frame is not captured
35. How do we fight against these devils in Ruby? runtime checks - Guards - If check fails, go back to interpreter (deoptimization). - Some runtime overhead - version - receiver’s class - constant cache - frame capture
36. How do we fight against these devils in Ruby? compile time assumptions - If method call is assumed to be dangerous, stop compiling and continue interpreter execution. - eval - binding
37. How do we fight against these devils in Ruby? Patch Point (binary patches) - Prepare memory space for patching in advance - No runtime penalty - If disaster occurs, rewrite all patch points. - re-definition of basic operations (i.e. Integer#+) - TracePoint
38. Let`s fight against Ruby devils inside Ruby.
39. Some demos?