Re: with-foreign-object allocation question

If LW's alloca is like C's, then presumably the thing is on the stack and is probably 'legal' until something else overwrites it with probably-bad results?

--tim

> On 10 Apr 2026, at 09:51, Madhu (as enometh at meer dot net) <[email protected]> wrote:
> 
> sorry for the immediate followup:
> 
> actuallythere is a another deeper problem because ARGS may be used
> after it is freed, it really should be allocated and not freed, but
> that is not the point of failure in other lisps, or on lispworks,
> 
> *  In  <[email protected]>
> I wrote on Fri, 10 Apr 2026 14:08:38 +0530 (IST)
> 
>> I am trying to fix a lethal memory bug in
>> https://github.com/StjepanPoljak/musicli src/jack.c: (start-jack-callbacks)
>> where there is a call
>> 
>>  (cffi:with-foreign-object (args '(:pointer (:struct jack-cb-args)))
>>     ... clobber 24 bytes == (sizeof (:struct jack-cb-args))
>>        allocated at ARGS ...)
>> 
>> which should really read
>> 
>>  (cffi:with-foreign-object '(:struct jack-cb-args) ...)
>> 
>> this reliably crashes other lisps, but not lwl 64 personal.  what
>> could be the reason for this resiliance? macroexpansion on the
>> incorrect form shows
>> 
>> (fli:with-dynamic-foreign-objects nil
>>  (let* ((#:size6844 8)
>>         (args (fli:alloca :type :byte :nelems #:size6844)))
>> 
>> Which shows only 8 bytes being allocated. but are allocations aligned
>> at > 24byte offsets, so the memory corruption doesn't show up in
>> lispworks in this case?
>> 
>> -- Madhu
>> 
>> (project author bcc'd)
> 
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