On 01/22/2018 01:54 PM, Martin Kletzander wrote:
> On Mon, Jan 22, 2018 at 01:47:24PM +0100, Michal Privoznik wrote:
>> On 01/22/2018 01:22 PM, Daniel P. Berrange wrote:
>>> On Mon, Jan 22, 2018 at 12:49:12PM +0100, Martin Kletzander wrote:
>>>> On Thu, Jan 18, 2018 at 10:16:55AM +0100, Ján Tomko wrote:
>>>>> After the latest CPU additions, the build fails with clang:
>>>>> cputest.c:905:1: error: stack frame size of 26136 bytes
>>>>> in function 'mymain' [-Werror,-Wframe-larger-than=]
>>>>>
>>>>> Raise the relaxed limit which is used for tests.
>>>>> ---
>>>>> m4/virt-compile-warnings.m4 | 2 +-
>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> Pushed as a build breaker fix
>>>>>
>>>>> diff --git a/m4/virt-compile-warnings.m4 b/m4/virt-compile-warnings.m4
>>>>> index f18a08a8f..b9c974842 100644
>>>>> --- a/m4/virt-compile-warnings.m4
>>>>> +++ b/m4/virt-compile-warnings.m4
>>>>> @@ -200,7 +200,7 @@ AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[
>>>>> # but using 1024 bytes sized buffers (mostly for virStrerror)
>>>>> # stops us from going down further
>>>>> gl_WARN_ADD([-Wframe-larger-than=4096],
>>>>> [STRICT_FRAME_LIMIT_CFLAGS])
>>>>> - gl_WARN_ADD([-Wframe-larger-than=25600],
>>>>> [RELAXED_FRAME_LIMIT_CFLAGS])
>>>>> + gl_WARN_ADD([-Wframe-larger-than=32768],
>>>>> [RELAXED_FRAME_LIMIT_CFLAGS])
>>>>>
>>>>
>>>> Remind me again why don't we do -Wno-frame-larger-than (or something
>>>> to that
>>>> effect) for tests? Is it just because "We should fix it at some
>>>> point"? I
>>>> can't really recall the reasoning behind that (and if it is still
>>>> valid) even
>>>> though I already asked for it.
>>>
>>> I don't think there's a strong reason, given the way we currently write
>>> tests with huge amounts of stack variables.
>>>
>>> For -Wframe-larger-than to be useful, we'd need to move all the big data
>>> blobs to be static, global variables.
>> Or simply use compiler that honours variable lifetime. If a variable is
>> defined only in a block, compiler should be able to just reuse the
>> stack. I mean for the following case:
>>
>> do {
>> int x;
>> } while (0);
>>
>> do {
>> int y;
>> } while (0);
>>
>> I don't see any compelling reason for compiler to reserve two ints on
>> the stack. Or if it does, count it as one when comparing agains
>> -Wframe-larger-than.
>>
>
> We can do that ourselves, even though it's not really great thing to
> do. Just
> reset the one struct and reuse it. I added it (and future research) as
> an idea
> to GSoC ideas. Let's see if someone rewrites that.
I don't think that's a good idea. It's working around broken compiler.
Just like the original patch (which we unfortunately have to have).
Michal
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