On 06/05/19 18:23, Daniel P. Berrangé wrote: > On Wed, Jun 05, 2019 at 06:18:38PM +0200, Laszlo Ersek wrote: >> On 06/05/19 16:23, Daniel P. Berrangé wrote: >>> On Tue, May 28, 2019 at 08:12:24PM +0200, Markus Armbruster wrote: >>>> We have a bunch of headers without multiple inclusion guards. Some are >>>> clearly intentional, some look accidental. Too many for me to find out >>>> by examining each of them, so I'm asking their maintainers. >>>> >>>> Why do I ask? I'd like to mark the intentional ones and fix the >>>> accidental ones, so they don't flunk "make check-headers" from "[RFC v4 >>>> 0/7] Baby steps towards saner headers" just because they lack multiple >>>> inclusion guards. >>>> >>>> Just in case: what's a multiple inclusion guard? It's >>>> >>>> #ifndef UNIQUE_GUARD_SYMBOL_H >>>> #define UNIQUE_GUARD_SYMBOL_H >>>> ... >>>> #endif >>>> >>>> with nothing but comments outside the conditional, so that the header >>>> can safely be included more than once. >>> >>> Any opinions on using the less verbose syntax instead: >>> >>> #pragma once >>> >>> It is not portable C, but we explicitly only care about GCC or CLang, >>> so portability isn't an issue for us. >> >> I don't feel strongly about this particular question, so if folks prefer >> "#pragma once", I won't complain. I'd just like to report that section 6 >> of "HACKING" appears the opposite of "we explicitly only care about GCC >> or CLang". > > Heh, yeah that doc does require some updating, as we certainly don't > require conformance to the vanilla C standard any more. We now explicitly > request "-std=gnu99" as the conformance level which allows many GNU > extensions to the standard. > > commit 7be41675f7cb16be7c8d2554add7a63fa43781a8 > Author: Thomas Huth <th...@redhat.com> > Date: Mon Jan 7 11:25:22 2019 +0100 > > configure: Force the C standard to gnu99 > > Different versions of GCC and Clang use different versions of the C > standard. > This repeatedly caused problems already, e.g. with duplicated typedefs: > > https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg05829.html > > or with for-loop variable initializers: > > https://lists.gnu.org/archive/html/qemu-devel/2019-01/msg00237.html > > To avoid these problems, we should enforce the C language version to the > same level for all compilers. Since our minimum compiler versions is > GCC v4.8, our best option is "gnu99" for C code right now ("gnu17" is not > available there yet, and "gnu11" is marked as "experimental"), and > "gnu++98" > for the few C++ code that we have in the repository.
TIL :) Thanks! Laszlo > The HACKING docs predate this commit, and when reviewing, we failed to > notice we needed to update HACKING to match our new policy. > > Regards, > Daniel >
