gh-91869: Fix tracing of specialized instructions with extended args

Lib/importlib/_bootstrap_external.py

@@ -416,7 +416,7 @@ def _write_atomic(path, data, mode=0o666):
 # Whenever MAGIC_NUMBER is changed, the ranges in the magic_values array
 # in PC/launcher.c must also be updated.
 
-MAGIC_NUMBER = (3493).to_bytes(2, 'little') + b'\r\n'
+MAGIC_NUMBER = (3494).to_bytes(2, 'little') + b'\r\n'
 
 _RAW_MAGIC_NUMBER = int.from_bytes(MAGIC_NUMBER, 'little')  # For import.c
 

Lib/opcode.py

@@ -264,6 +264,9 @@ def jabs_op(name, op, entries=0):
         "COMPARE_OP_INT_JUMP",
         "COMPARE_OP_STR_JUMP",
     ],
+    "EXTENDED_ARG": [
+        "EXTENDED_ARG_QUICK",
+    ],
     "JUMP_BACKWARD": [
         "JUMP_BACKWARD_QUICK",
     ],

Lib/test/test_sys_settrace.py

@@ -2432,5 +2432,47 @@ def gen():
         output.append(5)
 
 
+class TestExtendedArgs(unittest.TestCase):
+
+    def setUp(self):
+        self.addCleanup(sys.settrace, sys.gettrace())
+        sys.settrace(None)
+
+    def count_traces(self, func):
+        # warmup
+        for _ in range(20):
+            func()
+
+        counts = {"call": 0, "line": 0, "return": 0}
+        def trace(frame, event, arg):
+            counts[event] += 1
+            return trace
+
+        sys.settrace(trace)
+        func()
+        sys.settrace(None)
+
+        return counts
+
+    def test_trace_unpack_long_sequence(self):
+        ns = {}
+        code = "def f():\n  (" + "y,\n   "*300 + ") = range(300)"
+        exec(code, ns)
+        counts = self.count_traces(ns["f"])
+        self.assertEqual(counts, {'call': 1, 'line': 301, 'return': 1})
+
+    def test_trace_lots_of_globals(self):
+        code = """if 1:
+            def f():
+                return (
+                    {}
+                )
+        """.format("\n+\n".join(f"var{i}\n" for i in range(1000)))
+        ns = {f"var{i}": i for i in range(1000)}
+        exec(code, ns)
+        counts = self.count_traces(ns["f"])
+        self.assertEqual(counts, {'call': 1, 'line': 2000, 'return': 1})
+
+
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Core and Builtins/2022-04-26-05-05-32.gh-issue-91869.ELbTXl.rst

@@ -0,0 +1 @@
+Fix an issue where specialized opcodes with extended arguments could produce incorrect tracing output or lead to assertion failures.

Python/ceval.c

@@ -5624,6 +5624,15 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
         }
 
         TARGET(EXTENDED_ARG) {
+            assert(oparg);
+            oparg <<= 8;
+            oparg |= _Py_OPARG(*next_instr);
+            opcode = _PyOpcode_Deopt[_Py_OPCODE(*next_instr)];
+            PRE_DISPATCH_GOTO();
+            DISPATCH_GOTO();
+        }
+
+        TARGET(EXTENDED_ARG_QUICK) {
             assert(oparg);
             oparg <<= 8;
             oparg |= _Py_OPARG(*next_instr);

Python/compile.c

@@ -211,13 +211,13 @@ write_instr(_Py_CODEUNIT *codestr, struct instr *instruction, int ilen)
     int caches = _PyOpcode_Caches[opcode];
     switch (ilen - caches) {
         case 4:
-            *codestr++ = _Py_MAKECODEUNIT(EXTENDED_ARG, (oparg >> 24) & 0xFF);
+            *codestr++ = _Py_MAKECODEUNIT(EXTENDED_ARG_QUICK, (oparg >> 24) & 0xFF);
             /* fall through */
         case 3:
-            *codestr++ = _Py_MAKECODEUNIT(EXTENDED_ARG, (oparg >> 16) & 0xFF);
+            *codestr++ = _Py_MAKECODEUNIT(EXTENDED_ARG_QUICK, (oparg >> 16) & 0xFF);
             /* fall through */
         case 2:
-            *codestr++ = _Py_MAKECODEUNIT(EXTENDED_ARG, (oparg >> 8) & 0xFF);
+            *codestr++ = _Py_MAKECODEUNIT(EXTENDED_ARG_QUICK, (oparg >> 8) & 0xFF);
             /* fall through */
         case 1:
             *codestr++ = _Py_MAKECODEUNIT(opcode, oparg & 0xFF);
@@ -8254,6 +8254,7 @@ fix_cell_offsets(struct compiler *c, basicblock *entryblock, int *fixedmap)
             struct instr *inst = &b->b_instr[i];
             // This is called before extended args are generated.
             assert(inst->i_opcode != EXTENDED_ARG);
+            assert(inst->i_opcode != EXTENDED_ARG_QUICK);
             int oldoffset = inst->i_oparg;
             switch(inst->i_opcode) {
                 case MAKE_CELL: