On 04/06/2017 05:28, kefu chai wrote: > On Sat, Jun 3, 2017 at 2:50 AM, Willem Jan Withagen <wjw@xxxxxxxxxxx> wrote: >> Hi, >> >> Now that we have -Wvla set: >> === >> Adds C++ warning flag for C Variable-Length Arrays. >> >> C VLAs are not supported in C++. However, the GNU compiler allows >> them as an extension, which it does not warn about when not in >> pedantic mode. Unfortunately, it's easy to accidentally write >> a VLA, even unintentionally-- adding this warning will help us >> catch that. >> === >> >> Are there going to be attempts to eradicate this usage? >> Note that Clang also supports VLAs: >> === >> GCC and C99 allow an array's size to be determined at run time. This >> extension is not permitted in standard C++. However, Clang supports such >> variable length arrays for compatibility with GNU C and C99 programs. >> === >> > > it's not in C++11 standard. but it's a handy feature in practice. i > still have trouble understanding we want to have -Wvla. i was trying > to silence this warning option last night but failed to move further > after several attempts. see https://github.com/ceph/ceph/pull/15441. > > probably, Jesse have more insights on this. It starts with old discussions from before 2009, and it would be hard for compiler makers to actually build it. Both GCC and Clang support it. And next the major complaint I find about it, is that these structures are build on the stack, which might cause stackoverlows (and that mostly on embedded computers) That would be something for programmers to be aware of. And C++ has other stuctures to implement these. But as you tried, it is nog going to be easy. I would probably think there are beter things to do, than to chase after this. And IMHO the order should have been: Fix the VLAs and only then turn the warning on on the master repo. As to not have every body start looking at these warning that have just started to pop up. But perhaps that is just me, because each and every warning is again a case where I need to look for possible incompatabilities. --WjW -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
