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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Nov 01, 2019 at 02:36:03PM +0000, Mark Rutland wrote: > On Fri, Nov 01, 2019 at 11:11:49AM +0000, Robin Murphy wrote: > > On 2019-11-01 10:55 am, Will Deacon wrote: > > > On Fri, Nov 01, 2019 at 10:54:21AM +0000, Robin Murphy wrote: > > > > On 2019-11-01 10:36 am, Will Deacon wrote: > > > > > On Fri, Nov 01, 2019 at 08:53:19AM +0000, Mark Rutland wrote: > > > > > > You need want &(obj.attr.attr) rather than &(obj).attr.attr, i.e. > > > > > > > > > > > > #define ARMV8_EVENT_ATTR(name, config) \ > > > > > > (&((struct perf_pmu_events_attr) { \ > > > > > > .attr = __ATTR(name, 0444, armv8pmu_events_sysfs_show, NULL), \ > > > > > > .id = config, \ > > > > > > }.attr.attr)) > > > > > > ... which compiles for me. > > > > > > > > > > Weird, the following compiles fine for me with both GCC and clang: > > > > > > > > > > #define ARMV8_EVENT_ATTR(name, config) \ > > > > > (&((struct perf_pmu_events_attr) { \ > > > > > .attr = __ATTR(name, 0444, armv8pmu_events_sysfs_show, NULL), \ > > > > > .id = config, \ > > > > > }).attr.attr) > > > > > > > > You know that the expressions are equivalent because unary "&" has lower > > > > precedence than ".", right? ;) > > > > > > Right, which is why it's weird that Shaokun claims that the version I posted > > > doesn't compile. I assume it didn't build for Mark either, hence his extra > > > brackets. > > I must've meessed up locally -- sorry for the noise. > > > Because different compilers have different ideas of whether "obj" is a valid > > thing to dereference at all, regardless of where you put parentheses. From > > what I remember, the array trick was the only way to convince older GCCs to > > treat the floating struct initialiser as an actual object definition. I > > guess newer versions are a bit more lenient. > > I strongly suspect Will's (much cleaner) version would work with those older > compilers too, and I just didn't know what I was doing ~8 years ago when I came > up with the trick. > > I can have a go with my toolchain museum on Monday; if old GCCs are happy we > can clean up the other instances of the trick to be much more legible. I've thrown it into -next to see how it gets on. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel