Re: RFA/RFC: Add stack recursion limit to libiberty's demangler

[Nick Clifton <nickc at redhat dot com>]

Hi Jakub,

>>   Also - Tom and Pedro have raised the issue that the patch introduces
>>   a new static variable to the library that is not thread safe.  I am
>>   not sure of the best way to address this problem.  Possibly the
>>   variable could be made thread local ?  Are there any other static
> 
> Please don't.

OK. :-)

> Most of the demangler functions pass around a pointer to a struct with
> context, can't this be added in there?

Not without modifying the current demangling interface.  The problem is 
that the context structure is created for each invocation of a demangling 
function (from outside the library), and no state is preserved across 
demangling calls.  Thus in order to have a recursion limit which is 
configurable by the caller, you either need to have a global variable or 
else extend the demangling interface to include a recursion limit parameter.

I did consider just having a fixed limit, that the user cannot change, but
I thought that this might be rejected by reviewers.  (On the grounds that
different limits are appropriate to different execution environments).
Note - enabling or disabling the recursion limit is controlled by a separate
feature of the proposed patch, ie the new DMGL_RECURSE_LIMIT flag in the 
options field of the cplus_demangleXXX() functions.  But there is not enough
room in the options field to also include a recursion limit value.

Cheers
  Nick