Re: [PATCH] nptl: Add compiler barrier in nptl/tst-pthread-getattr

[Florian Weimer <fweimer at redhat dot com>]

* Andreas Schwab:

> On Jul 29 2019, Florian Weimer <fweimer@redhat.com> wrote:
>
>> * Carlos O'Donell:
>>
>>>> tst-pthread-getattr.c: In function ‘allocate_and_test’:
>>>> tst-pthread-getattr.c:54:10: error: function returns address of local variable [-Werror=return-local-addr]
>>>>     54 |   return mem;
>>>>        |          ^~~
>>>> In file included from ../include/alloca.h:3,
>>>>                   from tst-pthread-getattr.c:26:
>>>> ../stdlib/alloca.h:35:23: note: declared here
>>>>     35 | # define alloca(size) __builtin_alloca (size)
>>>>        |                       ^~~~~~~~~~~~~~~~~~~~~~~
>>>> tst-pthread-getattr.c:51:9: note: in expansion of macro ‘alloca’
>>>>     51 |   mem = alloca ((size_t) (mem - target));
>>>>        |         ^~~~~~
>>>>
>>>> The address itself is used in a check in the caller, so using
>>>> uintptr_t instead is reasonable.
>>>
>>> Any reason why we wouldn't move the test into the function?
>>
>> I think printf might fault because of its own stack usage (which can
>> easily exceed half a page in some cases).
>
> Then return only the value of the same-page check and print it in the
> parent.

Sorry, what do you mean?  I think the write location is printed for
diagnostics.  And my patch turns this into uintptr_t, suppressing the
compiler warning.

Thanks,
Florian