Thread (42 messages) 42 messages, 9 authors, 2017-06-22

Re: [PATCH 6/7] md/raid10, LLVM: get rid of variable length array

From: Peter Zijlstra <peterz@infradead.org>
Date: 2017-03-17 12:10:00
Also in: linux-crypto, linux-kbuild, lkml

On Thu, Mar 16, 2017 at 05:15:19PM -0700, Michael Davidson wrote:
quoted hunk ↗ jump to hunk
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 <redacted>
---
 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?
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