On Fri, Mar 17, 2017 at 01:31:23PM +0100, Alexander Potapenko 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 > 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) Be that as it may; what you construct above is disgusting. Surely the code can be refactored to not look like dog vomit? Also; its not immediately obvious conf->copies is 'small' and this doesn't blow up the stack; I feel that deserves a comment somewhere. -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html