Messages in this thread | | | From | Nick Desaulniers <> | Date | Fri, 20 Oct 2017 00:15:55 -0700 | Subject | Re: [PATCH] cgroup: reorder flexible array members of struct cgroup_root |
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On Wed, Oct 18, 2017 at 6:30 AM, Tejun Heo <tj@kernel.org> wrote: > On Mon, Oct 16, 2017 at 11:33:21PM -0700, Nick Desaulniers wrote: >> When compiling arch/x86/boot/compressed/eboot.c with HOSTCC=clang, the >> following warning is observed: >> >> ./include/linux/cgroup-defs.h:391:16: warning: field 'cgrp' with >> variable sized type 'struct cgroup' not at the end of a struct or class >> is a GNU extension [-Wgnu-variable-sized-type-not-at-end] >> struct cgroup cgrp; >> ^ >> Flexible array members are a C99 feature, but must be the last member of >> a struct. Structs with flexible members composed in other structs must >> also be the final members, unless using GNU C extensions. >> >> struct cgroup_root's member cgrp is a struct cgroup, struct cgroup's >> member ancestor_ids is a flexible member. > > This is silly tho. We know the the root group embedded there won't > have any ancestor_ids.
Sure, but struct cgroup_root is still declared as having a struct cgroup not declared as the final member.
> Also, in general, nothing prevents us from > doing something like the following. > > struct outer_struct { > blah blah; > struct inner_struct_with_flexible_array_member inner; > unsigned long storage_for_flexible_array[NR_ENTRIES]; > blah blah; > };
At that point, then why have the struct with flexible array member in the first place?
>> or specific location of the member cgrp within struct cgroup_root AFAICT. > I think we should just silence the bogus warning.
Is the order of the members actually important? Otherwise it seems that we're taking advantage of a GNU C extension for no real reason, which is what I'm trying to avoid. Please reconsider.
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