[Python-Dev] recursion limit in marshal

Neal Norwitz nnorwitz at gmail.com
Fri May 18 07:21:05 CEST 2007

I had a little argument with the marshal module on Windows last night,
I eventually won. :-)

A patch was checked in which would prevent blowing out the stack and
segfaulting with this code:

    marshal.loads( 'c' + ('X' * 4*4) + '{' * 2**20)

Originally, I didn't change the recursion limit which was 5000.  (See
MAX_MARSHAL_STACK_DEPTH in Python/marshal.c)  This is a constant in C
code that cannot be changed at runtime.  The fix worked on most
platforms.  However it didn't on some (Windows and MIPS?), presumably
due a smaller stack limit.  I don't know what the stack limits are on
each architecture.

I dropped the limit to 4000, that still crashed.  I eventually settled
on 2000.  Which passed in 2.6.  I don't think there is a test case for
the recursion limit when dumping a deeply nested object.  I suppose I
should add one, because that could also blow the limit too.

The point of this message is to see if anyone thinks 2000 is
unreasonable.  It could probably be raised, but I'm not going to try
it since I don't have access to a Windows box.  Testing this remotely


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