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

[Florian Weimer <fweimer at redhat dot com>]

* Andreas Schwab:

> On Jul 30 2019, Florian Weimer <fweimer@redhat.com> wrote:
>
>> * 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?
>
> If you don't want to print it in allocate_and_test, print it in main.

Do you mean to print it in check_stack_top?  That's what the current
code does.

Thanks,
Florian