[PATCH 0/7] RFC Memory tagging support

[Florian Weimer]

* Szabolcs Nagy:

> The 06/15/2020 15:40, Richard Earnshaw wrote:
>> 2) Tests that assume that malloc_usable_size will return a specific
>> amount of free space.  The assumptions are not correct, because the
>> tag colouring boundaries needed for MTE means that the 8 bytes in the
>> block containing the back pointer can no-longer be used by users when
>> we have MTE (they have a different colour that belongs to the malloc
>> data structures).
>
> with --enable-memory-tagging i see
>
> FAIL: malloc/tst-malloc-usable
> FAIL: malloc/tst-malloc-usable-static
> FAIL: malloc/tst-malloc-usable-static-tunables
> FAIL: malloc/tst-malloc-usable-tunables
>
> malloc_usable_size(malloc(7)) is 16 with
> MALLOC_CHECK_=0 and it's 0 with MALLOC_CHECK_=3.
>
> i think this breaks existing usage, so either
> malloc check should be disabled if memory tagging
> is enabled or fixed to be compatible.
> (or at least the issue should be documented)

I'm with Richard here—this is an incorrect test expectation, not a bug
in the implementation.

Thanks,
Florian