I'm having a hard time debugging some virtual machine code because GDB won't break where it's supposed to. Here's my breakpoint #2: 2 breakpoint keep y 0x00005555556914fd ceval_reg.h:_PyEval_EvalFrameDefault:TARGET_JUMP_IF_FALSE_REG breakpoint already hit 1 time p/x oparg p (oparg >> 16) & 0xff | (oparg >> 8) & 0xff p oparg & 0xff p *fastlocals@4 but when it breaks, it's not at the beginning of the case (that is, where the TARGET_JUMP_IF_FALSE_REG label is defined), but inside the SETLOCAL macro of the COMPAR_OP_REG case! (That is, it's not anywhere close to the correct place.) case TARGET(COMPARE_OP_REG): { int dst = REGARG4(oparg); int src1 = REGARG3(oparg); int src2 = REGARG2(oparg); int cmpop = REGARG1(oparg); assert(cmpop <= Py_GE); PyObject *left = GETLOCAL(src1); PyObject *right = GETLOCAL(src2); PyObject *res = PyObject_RichCompare(left, right, cmpop); *SETLOCAL(dst, res);* if (res == NULL) goto error; DISPATCH(); } It actually breaks in the Py_XDECREF which is part of the SETLOCAL macro: #define SETLOCAL(i, value) do { PyObject *tmp = GETLOCAL(i); \ GETLOCAL(i) = value; \ *Py_XDECREF(tmp)*; } while (0) (actually, in the Py_DECREF underneath the Py_XDECREF macro). I've configured like so: ./configure --with-pydebug --with-tracerefs --with-assertions Python/ceval.c is compiled with this GCC command: gcc -pthread -c -Wno-unused-result -Wsign-compare -g -Og -Wall -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -Wstrict-prototypes -Werror=implicit-function-declaration -fvisibility=hidden -I./Include/internal -I. -I./Include -DPy_BUILD_CORE -o Python/ceval.o Python/ceval.c I don't know if this is a GCC problem, a GDB problem, or a Skip problem. Is there more I can do to help the tool chain break at the correct place? It seems that if I break at a hard line number, GDB does the right thing, but I'd kind of prefer to use the symbolic label instead. I rather like the notion of breaking at a label name, but if GCC/GDB can't figure things out, I guess I'll have to live with line numbers. Thanks, Skip