ZJIT: Fix test_exit_tracing for Perfetto FXT output

Author: tekknolagi

test/ruby/test_zjit.rb

@@ -383,25 +383,20 @@ def test
   end
 
   def test_exit_tracing
-    # This is a very basic smoke test. The StackProf format
-    # this option generates is external to us.
-    Dir.mktmpdir("zjit_test_exit_tracing") do |tmp_dir|
-      assert_compiles('true', <<~RUBY, extra_args: ['-C', tmp_dir, '--zjit-trace-exits'])
-        def test(object) = object.itself
-
-        # induce an exit just for good measure
-        array = []
-        test(array)
-        test(array)
-        def array.itself = :not_itself
-        test(array)
-
-        RubyVM::ZJIT.exit_locations.is_a?(Hash)
-      RUBY
-      dump_files = Dir.glob('zjit_exits_*.dump', base: tmp_dir)
-      assert_equal(1, dump_files.length)
-      refute(File.empty?(File.join(tmp_dir, dump_files.first)))
-    end
+    # Smoke test: --zjit-trace-exits writes a Fuchsia trace (.fxt) file to /tmp
+    assert_compiles('true', <<~RUBY, extra_args: ['--zjit-trace-exits'])
+      def test(object) = object.itself
+
+      # induce an exit just for good measure
+      array = []
+      test(array)
+      test(array)
+      def array.itself = :not_itself
+      test(array)
+
+      fxt_files = Dir.glob("/tmp/perfetto-\#{Process.pid}.fxt")
+      fxt_files.length == 1 && !File.empty?(fxt_files.first)
+    RUBY
   end
 
   private

zjit/src/stats.rs

@@ -976,7 +976,7 @@ pub fn zjit_alloc_bytes() -> usize {
 /// Fuchsia Trace Format (FXT) binary writer for --zjit-trace-exits.
 /// Produces .fxt files that can be opened directly in Perfetto UI.
 /// Uses the string table for deduplication of repeated reason/frame strings.
-/// See: https://fuchsia.dev/fuchsia-src/reference/tracing/trace-format
+/// See: <https://fuchsia.dev/fuchsia-src/reference/tracing/trace-format>
 pub struct PerfettoTracer {
     writer: std::io::BufWriter<std::fs::File>,
     start_time: std::time::Instant,