[Python-Dev] Re: Another test_compiler mystery

[Tim Peters]

Here's some puzzling evidence (WinXP Pro SP1).  The test driver, for
convenience:

"""
import compiler, sys

f = open('../Lib/test/test_parser.py')
guts = f.read()
f.close()

def ouch(n):
    if n == 0:
        return compiler.compile(guts, "<string>", "exec")
    else:
        return ouch(n-1)

for n in range(0, 50):
    try:
        ouch(n)
        msg = 'ok'
    except KeyboardInterrupt:
        raise
    except Exception, msg:
        msg = str(sys.exc_info()[0]) + ' ' + str(msg)
    print n, msg
"""

The loop starts at 0 this time, and I'm only looking at a debug-build Python.

The stack size for an .exe can be specified to 4-byte granularity. 
Here's the largest stack size at which that produces no output at all:

C:\Code\python\PCbuild>editbin /stack:1310720 python_d.exe
Microsoft (R) COFF Binary File Editor Version 6.00.8447
Copyright (C) Microsoft Corp 1992-1998. All rights reserved.

C:\Code\python\PCbuild>python_d temp.py

C:\Code\python\PCbuild>echo %ERRORLEVEL%
128


Add 4 measly bytes, and it's a world of difference:

C:\Code\python\PCbuild>editbin /stack:1310724 python_d.exe
Microsoft (R) COFF Binary File Editor Version 6.00.8447
Copyright (C) Microsoft Corp 1992-1998. All rights reserved.



C:\Code\python\PCbuild>python_d temp.py
0 ok
1 ok
...
41 ok
42 ok

C:\Code\python\PCbuild>echo %ERRORLEVEL%
128

So it still vanishes early, but gets thru the entire
compiler.compile() business + 42 additional stacked Python calls! 
That's awfully impressive for four bytes.  That suggests "the problem"
isn't in detecting Python-level recursion.

Under the debugger, it dies with an access violation at that point. 
Alas, the C-level Python call stack is no longer anywhere in evidence
then.  Instead it's 7 levels deep in ntdll.dll, and is "in the middle"
of four consecutive Pentium PUSH instructions.  That's evidence that
the stack has been blown <wink>.

The debugger Output window does show ntdll.dll suffering a Stack
Overflow exception.  It then shows a variety of Access Violations in
ntdll.dll trying to read and write various locations, presumably in a
failing attempt to report the stack overflow.