Malloc tests

[zack leung]

There a way to get the same values used to make the calculation  in malloc
get usable size?
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Il ven 7 gen 2022, 21:25 zack leung <zakthertemsdev at gmail.com> ha scritto:

> I think that the malloc tests is calculated differently than  alloc_size+
> allocsize mod it looks like this
>  *alloc_size = (uintptr_t) next_block + HEAP_ALLOC_BONUS - alloc_begin;
> when i run the comparison  i get 8 (with heap alignment) and the function
> gives me 12.
>  is the heap alloc bonus part of the current block?
>
> On Thu, 6 Jan 2022 at 21:28, Joel Sherrill <joel at rtems.org> wrote:
>
>> On Thu, Jan 6, 2022 at 2:55 PM Gedare Bloom <gedare at rtems.org> wrote:
>> >
>> > On Tue, Jan 4, 2022 at 6:10 PM zack leung <zakthertemsdev at gmail.com>
>> wrote:
>> > >
>> > > Helllo  ,
>> > > I'm working on a patch for malloc_get_usable size right now so far i
>> have
>> > > this test case for malloc, I just make sure that the value is null
>> and i
>> > > just malloc an int and then  i make a call to the function
>> malloc_usable
>> > > size and then i compare it like this.
>> > >
>> > > static void test_malloc_usablesize( void ){
>> > >    int * a = malloc(sizeof(int));
>> > >    rtems_test_assert((int) malloc_usable_size(a) == 12);
>> > >    free (a);
>> > >
>> > >    int * b = NULL;
>> > >    rtems_test_assert( 0 == malloc_usable_size(b));
>> > >    free(b);
>> > >
>> > >
>> > > }
>> > > Is there a good amount of storage to allocate? Also I heard someone
>> made a
>> >
>> > I think that this test case is quite brittle. The "usable size" will
>> > depend on the implementation details of malloc, and the conditions of
>> > the heap when the allocation request gets made. I don't have better
>> > ideas however for how to test the correctness of the usable_size
>> > function. Maybe there are certain sequences of malloc/free calls that
>> > can be relied upon to give you deterministic sizes of allocations?
>>
>> My suggestion in private chat was that you can depend on the
>> malloc heap being initialized with CPU_HEAP_ALIGNMENT. That's
>> what that macro is specifically for. It is used in
>> include/rtems/score/wkspaceinit*.h
>> and has been since the dawn of time.
>>
>> Then the size for a valid pointer from malloc() should be between
>> the allocated size and the next number on a CPU_HEAP_ALIGNMENT
>> boundary. I think the exact number is actually something like this:
>>
>> expected = alloc_size;
>> mod = alloc_size % CPU_HEAP_ALIGMENT;
>> expected += mod;
>>
>> Adding a helper function in the test to compute the expected
>> size allocated and validate the return may be wise if multiple
>> size allocations are going to be tested.
>>
>>
>> > > formatter for rtems source files.  Can someone tell me how to use it
>> and if
>> > > it is on the main branch?
>> >
>> > This was part of a gsoc project last year. We haven't quite made the
>> > switch over to it and the associated coding style I think, but you can
>> > find the code via
>> >
>> https://devel.rtems.org/wiki/GSoC/2021#StudentsSummerofCodeTrackingTable
>> > the student was Meh Mbeh Ida Delphine
>> >
>> >
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>