From: "jacobcarlborg (Jacob Carlborg) via ruby-core" <ruby-core@...>
Date: 2025-01-20T12:41:08+00:00
Subject: [ruby-core:120745] [Ruby master Bug#14582] Unable to use `method__entry` and `method_return` tracing probes since 2.5

Issue #14582 has been updated by jacobcarlborg (Jacob Carlborg).


I'm really interested in using DTrace on Ruby as well. One of the major advantages of DTrace is that it's always available and doesn't require any code changes or restarts of the system that is being instrumented. But with the current way that USDT probes are implemented in Ruby it defeats many of the advantages of DTrace.

----------------------------------------
Bug #14582: Unable to use `method__entry` and `method_return` tracing probes since 2.5
https://bugs.ruby-lang.org/issues/14582#change-111578

* Author: guilhermereiscampos (Guilherme Reis Campos)
* Status: Open
* ruby -v: 2.5
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
Hi,

I am trying to use dtrace/systemtap probes and not being able to use it after the 2.5. The 2.4 version works fine. I was hoping this was fixed on 2.6-preview, but apparently not (just downloaded dev and tested).

I tried on OSX using dtrace and also on ubuntu (vagrant). 

```
# test.rb
class Foo

  def bar
    100.times { "Bar" }
  end
end

foo = Foo.new
foo.bar
# test.stp
probe process("/home/vagrant/.rbenv/versions/2.4.0/bin/ruby").mark("method__entry") # you will need to change this to your ruby path of your version.
{
	printf("%s => %s.%s in %s:%d\n", thread_indent(1), kernel_string($arg1),kernel_string($arg2),kernel_string($arg3),$arg4);
}
probe process("/home/vagrant/.rbenv/versions/2.4.0/bin/ruby").mark("method__return")
{
    printf("%s <= %s.%s in %s:%d\n", thread_indent(-1), kernel_string($arg1),kernel_string($arg2),kernel_string($arg3),$arg4);
} 
```

dtrace was something similar to it.

I was expecting to see this output:

```
# lots of calls
# ....
# then:
  4090 ruby(9667):   <= Gem::Specification.unresolved_deps in /home/vagrant/.rbenv/versions/2.4.0/lib/ruby/2.4.0/rubygems/specification.rb:1298
  4095 ruby(9667):   => MonitorMixin.mon_exit in /home/vagrant/.rbenv/versions/2.4.0/lib/ruby/2.4.0/monitor.rb:197
  4100 ruby(9667):    => MonitorMixin.mon_check_owner in /home/vagrant/.rbenv/versions/2.4.0/lib/ruby/2.4.0/monitor.rb:247
  4104 ruby(9667):    <= MonitorMixin.mon_check_owner in /home/vagrant/.rbenv/versions/2.4.0/lib/ruby/2.4.0/monitor.rb:251
  4109 ruby(9667):   <= MonitorMixin.mon_exit in /home/vagrant/.rbenv/versions/2.4.0/lib/ruby/2.4.0/monitor.rb:204
  4283 ruby(9667):  <= Kernel.require in /home/vagrant/.rbenv/versions/2.4.0/lib/ruby/2.4.0/rubygems/core_ext/kernel_require.rb:55
  4303 ruby(9667): <= Kernel.require in /home/vagrant/.rbenv/versions/2.4.0/lib/ruby/2.4.0/rubygems/core_ext/kernel_require.rb:55
     0 ruby(9667): => Foo.bar in test.rb:3
    16 ruby(9667): <= Foo.bar in test.rb:5
```
(The output above is 2.4)

my ruby (all versions that I tested) was install with rb-env:
```
RUBY_CONFIGURE_OPTS='--enable-dtrace --disable-install-doc' rbenv install 2.5.0
```


I am happy to provide details if required.  I'd also be happy to fix it if I have guidance.

Thanks,





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