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

[Michal Privoznik]

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.

Michal