Re: Problem report #20

["Stuart D. Herring" <herring@lanl.gov>]

I previously wrote:

>> Event var_deref_model: Variable "preserve_ptr" tracked as NULL was
>> passed
>> to a function that dereferences it. [model]
>> Also see events: [var_compare_op]
>>
>> 2075 	  signal_before_change (start, end, preserve_ptr);
>
> signal_before_change() doesn't even -use- preserve_ptr (is that a bug?),
> much less dereference it.  No bug (here).

Dan pointed out that signal_before_change does use preserve_ptr via
macros.    (Thanks.)  But the macros check the pointer before using it, so
signal_before_change(...,NULL) is safe, and so prepare_to_modify_buffer
(still) has no bug; it only uses preserve_ptr by passing it to
signal_before_change, and so the pointer is allowed to be NULL.

Davis

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