Messages in this thread | | | Date | Thu, 26 Oct 2017 07:32:22 -0700 | From | Tejun Heo <> | Subject | Re: [PATCH] cgroup: reorder flexible array members of struct cgroup_root |
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Hello,
On Wed, Oct 25, 2017 at 02:54:23PM -0700, Matthias Kaehlcke wrote: > From your earlier comment I understand that there is no problem in > this case because we know that cgroup_root->cgrp will always be > empty. > > However in other instances the warning could point out actual errors > in the code, so I think it is good to have this warning generally > enabled. If cgroup_root was defined in a .c file we could consider to > disable the warning locally, but since the definition is in a header > that is widely included (indirectly through linux/cgroup.h and > net/sock.h) this doesn't seem to be an option. > > Is there a good reason for the current position of cgrp within > cgroup_root? If there are no drawbacks in moving it to the end of > the struct I think Nick's patch is a reasonable solution.
This all sounds really bogus to me. Let's say we have something like the following.
struct flex_struct { int array[]; };
And the following two usages.
1.
struct flex_struct *fs = kmalloc(sizeof(struct flex_struct) + N * sizeof(int));
2.
struct enclosing_struct es { struct flex_struct fs; int fs_array_storage[N]; };
struct enclosing_struct *es = kmalloc(sizeof(struct enclosing_struct));
So, you're saying #1 is okay but #2 is not, which is just silly. The compiler can't warn correctly about flex array members whether they're embedded or not. Nothing prevents somebody accessing beyond N in #1 either.
This effort seems really pointless to me. Let's please not waste any more bandwidth on this.
Thanks.
-- tejun
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