From: "znz (Kazuhiro NISHIYAMA) via ruby-core" <ruby-core@...>
Date: 2026-10-12T04:59:30+00:00
Subject: [ruby-core:127073] [Ruby Bug#22427] `--enable=zjit` does not enable ZJIT

Issue #22427 has been reported by znz (Kazuhiro NISHIYAMA).

----------------------------------------
Bug #22427: `--enable=zjit` does not enable ZJIT
https://bugs.ruby-lang.org/issues/22427

* Author: znz (Kazuhiro NISHIYAMA)
* Status: Open
* Assignee: jit
* ruby -v: ruby 4.1.0dev (2026-10-11T13:56:36Z v4.1.0-preview1 2d08b5f42f) +PRISM [x86_64-linux]
* Backport: 3.3: DONTNEED, 3.4: DONTNEED, 4.0: REQUIRED
----------------------------------------
`ruby --help` lists `zjit` under "Features" (`zjit  Method-based JIT compiler (default: disabled).`), but `--enable=zjit` alone does not enable ZJIT, while `--enable=yjit` does enable YJIT.

```
$ ruby -v
ruby 4.0.7 (2026-09-15 revision 229531a6cf) +PRISM [x86_64-linux]

$ ruby --enable=yjit -v
ruby 4.0.7 (2026-09-15 revision 229531a6cf) +YJIT +PRISM [x86_64-linux]
$ ruby --enable=yjit -e 'p RubyVM::YJIT.enabled?'
true

$ ruby --enable=zjit -v
ruby 4.0.7 (2026-09-15 revision 229531a6cf) +PRISM [x86_64-linux]
$ ruby --enable=zjit -e 'p RubyVM::ZJIT.enabled?'
false

$ ruby --zjit -v
ruby 4.0.7 (2026-09-15 revision 229531a6cf) +ZJIT +PRISM [x86_64-linux]
$ ruby --zjit -e 'p RubyVM::ZJIT.enabled?'
true
```

The same happens with `--enable-zjit` and with `RUBYOPT=--enable=zjit`. ZJIT is enabled as soon as any `--zjit-*` option is added (for example `--enable=zjit --zjit-call-threshold=30`), and also with `RUBY_ZJIT_ENABLE=1`.

The cause is in `ruby.c`. `--enable=zjit` only sets the feature bit. Later, `opt->zjit` is computed as

```c
#if USE_ZJIT
    if (FEATURE_SET_P(opt->features, zjit)) {
        bool rb_zjit_option_enable(void);
        opt->zjit = rb_zjit_option_enable(); // set opt->zjit for Init_ruby_description() and calling rb_zjit_init()
    }
#endif
```

and `rb_zjit_option_enable()` (zjit/src/options.rs) returns true only when the Rust-side `OPTIONS` has been initialized (`OPTIONS.as_ref().is_some_and(|opts| !opts.disable)`). `OPTIONS` is initialized by `rb_zjit_prepare_options()`, which is called for `--zjit*` (through `setup_zjit_options()`) and for `RUBY_ZJIT_ENABLE`, but not for `--enable=zjit`. So `opt->zjit` stays false and `rb_zjit_init(false)` is called. The YJIT counterpart, `rb_yjit_option_disable()`, has no such dependency, which is why `--enable=yjit` works.

Judging from the diff, this was introduced by commit:f84bbb4238 ("ZJIT: add support for lazy `RubyVM::ZJIT.enable`", 2025-11-17, included in 4.0.0). Before it, the code was

```c
    if (FEATURE_SET_P(opt->features, zjit) && !opt->zjit) {
        extern void rb_zjit_prepare_options(void);
        rb_zjit_prepare_options();
        opt->zjit = true;
    }
```

A possible fix is to prepare the options when the feature bit is set, before asking whether ZJIT should be enabled:

```c
#if USE_ZJIT
    if (FEATURE_SET_P(opt->features, zjit)) {
        // --enable=zjit sets the feature bit without going through setup_zjit_options()
        extern void rb_zjit_prepare_options(void);
        rb_zjit_prepare_options();
        bool rb_zjit_option_enable(void);
        opt->zjit = rb_zjit_option_enable();
    }
#endif
```

`rb_zjit_prepare_options()` already handles the already-initialized case, so `--zjit-*` options and `--zjit-disable` keep working. test/ruby/test_rubyoptions.rb does not exercise `--enable=yjit` or `--enable=zjit`, so a test for the `--enable=` form would also help.

Reproduced in the `ghcr.io/ruby/ruby:4.0` (4.0.7) and `ghcr.io/ruby/ruby:master` (4.1.0dev 2d08b5f42f) Docker images (x86_64-linux).




-- 
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