Test: log GC counts around rb_funcall

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: samuel-williams-shopify

.github/workflows/test-ruby-gc-bug.yaml

@@ -1,13 +1,10 @@
-name: Test Ruby GC Bug
-
-# Builds unfixed Ruby (no rb_gc_register_address in scheduler.c) and tests
-# whether the worker_pool.c fix alone is sufficient to prevent the crash.
+name: Test Ruby GC Bug — Disassembly Comparison
 
 on: [push, pull_request]
 
 jobs:
-  test:
-    name: io-event (worker_pool fix) vs unfixed Ruby
+  disassembly:
+    name: Compare disassembly (CASE_A vs CASE_B)
     runs-on: ubuntu-24.04
 
     steps:
@@ -18,16 +15,16 @@ jobs:
         sudo apt-get update -q
         sudo apt-get install -y --no-install-recommends \
           ruby bison libyaml-dev libgdbm-dev libreadline-dev libncurses5-dev \
-          liburing-dev autoconf automake gcc make
+          liburing-dev autoconf automake gcc make binutils
 
-    - name: Clone Ruby (unfixed master @ bug/blocking-operation-gc)
+    - name: Clone Ruby (bug/blocking-operation-gc)
       uses: actions/checkout@v4
       with:
         repository: samuel-williams-shopify/ruby
         ref: bug/blocking-operation-gc
         path: ruby-src
 
-    - name: Build Ruby (same flags as ruby-dev-builder head)
+    - name: Configure Ruby (once — same flags for both cases)
       working-directory: ruby-src
       run: |
         ./autogen.sh
@@ -37,21 +34,53 @@ jobs:
           --disable-install-doc \
           --enable-yjit \
           cppflags="-DENABLE_PATH_CHECK=0"
-        make -j$(nproc)
-        make install
-        echo "$HOME/.rubies/ruby-head/bin" >> $GITHUB_PATH
 
-    - name: Show Ruby version
-      run: ruby --version
+    - name: Build CASE_B — operation = get_blocking_operation (works)
+      working-directory: ruby-src
+      run: make -j$(nproc)
 
-    - name: Install bundler and gems
+    - name: Disassemble CASE_B
+      working-directory: ruby-src
       run: |
-        gem install bundler --no-document
-        bundle install
+        objdump -d --no-show-raw-insn -M intel libruby.so \
+          | awk '/^[0-9a-f]+ <rb_fiber_scheduler_blocking_operation_wait>:/{found=1} found{print} found && /^$/{exit}' \
+          > /tmp/case_b.asm
+        echo "CASE_B lines: $(wc -l < /tmp/case_b.asm)"
 
-    - name: Build io-event native extension
-      run: bundle exec bake build
+    - name: Patch to CASE_A — operation = NULL (fails)
+      working-directory: ruby-src
+      run: |
+        sed -i 's/rb_fiber_scheduler_blocking_operation_t \*operation = get_blocking_operation(blocking_operation);/rb_fiber_scheduler_blocking_operation_t *operation = NULL;/' scheduler.c
+        grep -n "operation = NULL\|operation = get_blocking" scheduler.c
+
+    - name: Build CASE_A
+      working-directory: ruby-src
+      run: make -j$(nproc)
 
-    - name: Run tests
-      timeout-minutes: 10
-      run: bundle exec bake test
+    - name: Disassemble CASE_A
+      working-directory: ruby-src
+      run: |
+        objdump -d --no-show-raw-insn -M intel libruby.so \
+          | awk '/^[0-9a-f]+ <rb_fiber_scheduler_blocking_operation_wait>:/{found=1} found{print} found && /^$/{exit}' \
+          > /tmp/case_a.asm
+        echo "CASE_A lines: $(wc -l < /tmp/case_a.asm)"
+
+    - name: Print diff
+      run: |
+        echo "=== CASE_A (operation=NULL, FAILS) ==="
+        cat /tmp/case_a.asm
+        echo ""
+        echo "=== CASE_B (operation=get_blocking_operation, WORKS) ==="
+        cat /tmp/case_b.asm
+        echo ""
+        echo "=== DIFF (A vs B) ==="
+        diff /tmp/case_a.asm /tmp/case_b.asm || true
+
+    - name: Upload disassembly artifacts
+      uses: actions/upload-artifact@v4
+      if: always()
+      with:
+        name: disassembly
+        path: |
+          /tmp/case_a.asm
+          /tmp/case_b.asm