On Fri, Mar 17, 2017 at 1:31 PM, Alexander Potapenko <glider@xxxxxxxxxx> wrote:
> On Fri, Mar 17, 2017 at 1:08 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>> On Thu, Mar 16, 2017 at 05:15:19PM -0700, Michael Davidson wrote:
>>> Replace a variable length array in a struct by allocating
>>> the memory for the entire struct in a char array on the stack.
>>>
>>> Signed-off-by: Michael Davidson <md@xxxxxxxxxx>
>>> ---
>>> drivers/md/raid10.c | 9 ++++-----
>>> 1 file changed, 4 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
>>> index 063c43d83b72..158ebdff782c 100644
>>> --- a/drivers/md/raid10.c
>>> +++ b/drivers/md/raid10.c
>>> @@ -4654,11 +4654,10 @@ static int handle_reshape_read_error(struct mddev *mddev,
>>> /* Use sync reads to get the blocks from somewhere else */
>>> int sectors = r10_bio->sectors;
>>> struct r10conf *conf = mddev->private;
>>> - struct {
>>> - struct r10bio r10_bio;
>>> - struct r10dev devs[conf->copies];
>>> - } on_stack;
>>> - struct r10bio *r10b = &on_stack.r10_bio;
>>> + char on_stack_r10_bio[sizeof(struct r10bio) +
>>> + conf->copies * sizeof(struct r10dev)]
>>> + __aligned(__alignof__(struct r10bio));
>>> + struct r10bio *r10b = (struct r10bio *)on_stack_r10_bio;
>>> int slot = 0;
>>> int idx = 0;
>>> struct bio_vec *bvec = r10_bio->master_bio->bi_io_vec;
>>
>>
>> That's disgusting. Why not fix LLVM to support this?
>
> IIUC there's only a handful of VLAIS instances in LLVM code, why not
Sorry, "kernel code", not "LLVM code".
> just drop them for the sake of better code portability?
> (To quote Linus, "this feature is an abomination":
> https://lkml.org/lkml/2013/9/23/500)
>
> --
> Alexander Potapenko
> Software Engineer
>
> Google Germany GmbH
> Erika-Mann-Straße, 33
> 80636 München
>
> Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle
> Registergericht und -nummer: Hamburg, HRB 86891
> Sitz der Gesellschaft: Hamburg
--
Alexander Potapenko
Software Engineer
Google Germany GmbH
Erika-Mann-Straße, 33
80636 München
Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
