[libvirt] [PATCH] Raise the frame limit for tests

[Martin Kletzander]

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.

>Michal
>
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