On Thu, Jun 6, 2013 at 11:34 AM, Thomas Chust <ch...@web.de> wrote: > On 2013-06-05 23:36, Felix wrote: > > From: Dan Leslie <d...@ironoxide.ca> > >> [...] > >> Basically, use C_alloc to allocate the memory required to host both > >> the List structure and the data it is to contain, then use the C_list > >> macro to patch it all together. > > > > Note that this code is not correct: C_alloc allocates on the C stack and > the > > data will be invalid once the function returns (Sorry). If this works, > then > > it is just coincidental! > > [...] > > Hello, > > when I first saw that code I thought that this must be incorrect, too. > Then I checked the CHICKEN documentation for foreign-safe-lambda and read: > > "This is similar to foreign-lambda, but also allows the called > function to call Scheme functions and allocate Scheme data-objects." > > Now I'm confused. Of course C_alloc allocates on the stack and of course > this can likely break if a function just returns some pointer to stack > allocated data. However C_return could magically copy the return value > to the second generation heap or similar trickery to actually make > foreign-safe-lambda and C_alloc interoperate correctly or one could > perhaps use a special call ABI to prevent stack corruption upon return > from a foreign-safe-lambda and salvage stack allocated objects. Is any > such strategy actually implemented? >
>From what I understand, this is exactly what foreign-primitive does: wraps C_return in a CPS, keeping the stack-allocation alive. I posted a question on a similar topic a while back: http://lists.gnu.org/archive/html/chicken-users/2012-03/msg00034.html K. > > But maybe the documentation is just misleading and wanted to say > something about temporary allocation for the lifetime of the function > instead. > > Ciao, > Thomas > > > -- > When C++ is your hammer, every problem looks like your thumb. > > > _______________________________________________ > Chicken-users mailing list > Chicken-users@nongnu.org > https://lists.nongnu.org/mailman/listinfo/chicken-users >
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