From 660b995365f719fa59ed6f2809bb1527e6470d14 Mon Sep 17 00:00:00 2001
From: viralpraxis <iaroslav2k@gmail.com>
Date: Sat, 30 Nov 2024 00:13:54 +0300
Subject: [PATCH] [Bug #20915] Fix SEGV with `TracePoint#parameters` and
 aliased C method

The following snippet results with a SEGV:

```ruby
C = Class.new do
  alias_method :new_to_s, :to_s
end

TracePoint.new(:c_call, &:parameters).enable { C.new.new_to_s }
```

at MRI 3.3.6 and ruby 3.4.0dev

The root cause of the issue lies in the `rb_tracearg_parameters` function
within the `RUBY_EVENT_C_RETURN` branch. Specifically, when the invoked
method is an alias for a C function,
`rb_method_entry_without_refinements(..., trace_arg->called_id, ...)`
may return NULL. In that case we can fallback to `trace_arg->id`.
---
 test/ruby/test_settracefunc.rb | 16 ++++++++++++++++
 vm_trace.c                     |  3 +++
 2 files changed, 19 insertions(+)

diff --git a/test/ruby/test_settracefunc.rb b/test/ruby/test_settracefunc.rb
index 472d66fbba..37358757a6 100644
--- a/test/ruby/test_settracefunc.rb
+++ b/test/ruby/test_settracefunc.rb
@@ -94,6 +94,22 @@ class TestSetTraceFunc < Test::Unit::TestCase
     assert_equal([[:req]], parameters)
   end
 
+  def test_c_call_aliased_method
+    # [Bug #20915]
+    klass = Class.new do
+      alias_method :new_method, :method
+    end
+
+    instance = klass.new
+    parameters = nil
+
+    TracePoint.new(:c_call) do |tp|
+      parameters = tp.parameters
+    end.enable { instance.new_method(:to_s) }
+
+    assert_equal([[:req]], parameters)
+  end
+
   def test_call
     events = []
     name = "#{self.class}\##{__method__}"
diff --git a/vm_trace.c b/vm_trace.c
index f7baf3b309..99e853f1b0 100644
--- a/vm_trace.c
+++ b/vm_trace.c
@@ -937,6 +937,9 @@ rb_tracearg_parameters(rb_trace_arg_t *trace_arg)
             const rb_method_entry_t *me;
             VALUE iclass = Qnil;
             me = rb_method_entry_without_refinements(trace_arg->klass, trace_arg->called_id, &iclass);
+            if (!me) {
+                me = rb_method_entry_without_refinements(trace_arg->klass, trace_arg->id, &iclass);
+            }
             return rb_unnamed_parameters(rb_method_entry_arity(me));
         }
         break;