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
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
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