SF bug #494668: PUSH() should assert-fail on overflow.

eval_frame():  Added asserts to the top of the eval loop, to verify
that the eval stack pointer is in bounds, plus some comments.

diff --git a/Python/ceval.c b/Python/ceval.c
index 94cf17e0d4580c9328ffbc3604ebfbb68ec6ee61..2feb123a9c6ff242b6d2891e1bd3b473684d01ab 100644 (file)
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -497,7 +497,7 @@ eval_frame(PyFrameObject *f)
 #ifdef DXPAIRS
        int lastopcode = 0;
 #endif
-       PyObject **stack_pointer;
+       PyObject **stack_pointer; /* Next free slot in value stack */
        register unsigned char *next_instr;
        register int opcode=0;  /* Current opcode */
        register int oparg=0;   /* Current opcode argument, if any */
@@ -586,7 +586,7 @@ eval_frame(PyFrameObject *f)
        next_instr = first_instr + f->f_lasti;
        stack_pointer = f->f_stacktop;
        assert(stack_pointer != NULL);
-       f->f_stacktop = NULL;
+       f->f_stacktop = NULL;   /* remains NULL unless yield suspends frame */
 
        if (tstate->use_tracing) {
                if (tstate->c_tracefunc != NULL) {
@@ -634,6 +634,8 @@ eval_frame(PyFrameObject *f)
        w = NULL;
 
        for (;;) {
+               assert(stack_pointer >= f->f_valuestack);       /* else underflow */
+               assert(STACK_LEVEL() <= f->f_stacksize);        /* else overflow */
                /* Do periodic things.  Doing this every time through
                   the loop would add too much overhead, so we do it
                   only every Nth instruction.  We also do it if