Re: build failure of next-20220811 due to d79b32c2e4a4 ("vdpa_sim_blk: add support for discard and write-zeroes")

[Nathan Chancellor <nathan@kernel.org>]

On Thu, Aug 11, 2022 at 06:22:54PM +0100, Sudip Mukherjee (Codethink) wrote:
> Hi All,
> 
> Not sure if it has been reported, builds of arm64 with clang failed to
> build next-20220811 with the error:
> 
> drivers/vdpa/vdpa_sim/vdpa_sim_blk.c:201:3: error: expected expression
>                 struct virtio_blk_discard_write_zeroes range;
>                 ^
> drivers/vdpa/vdpa_sim/vdpa_sim_blk.c:204:25: error: use of undeclared identifier 'range'
>                 if (to_pull != sizeof(range)) {
>                                       ^
> drivers/vdpa/vdpa_sim/vdpa_sim_blk.c:207:21: error: use of undeclared identifier 'range'
>                                 to_pull, sizeof(range));
>                                                 ^
> drivers/vdpa/vdpa_sim/vdpa_sim_blk.c:212:60: error: use of undeclared identifier 'range'
>                 bytes = vringh_iov_pull_iotlb(&vq->vring, &vq->out_iov, &range,
>                                                                          ^
> drivers/vdpa/vdpa_sim/vdpa_sim_blk.c:222:38: error: use of undeclared identifier 'range'
>                 sector = vdpasim64_to_cpu(vdpasim, range.sector);
>                                                    ^
> drivers/vdpa/vdpa_sim/vdpa_sim_blk.c:224:43: error: use of undeclared identifier 'range'
>                 num_sectors = vdpasim32_to_cpu(vdpasim, range.num_sectors);
>                                                         ^
> drivers/vdpa/vdpa_sim/vdpa_sim_blk.c:225:37: error: use of undeclared identifier 'range'
>                 flags = vdpasim32_to_cpu(vdpasim, range.flags);
>                                                   ^
> drivers/vdpa/vdpa_sim/vdpa_sim_blk.c:202:7: error: mixing declarations and code is incompatible with standards before C99 [-Werror,-Wdeclaration-after-statement]
>                 u32 num_sectors, flags;
>                     ^
> 8 errors generated.
> 
> 
> git bisect pointed to d79b32c2e4a4 ("vdpa_sim_blk: add support for discard and write-zeroes").
> And, reverting that commit has fixed the build failure.
> 
> I will be happy to test any patch or provide any extra log if needed.

I am very surprised GCC does not error out in the same way, since as far
as I understand it, labeled statements have to be followed by a
statement and a declaration is not a statement in C so braces are
needed. In fact, it seems like something changed (regressed?) between
GCC 10.x and 11.x?

https://godbolt.org/z/EYaGa1eE3

I am going to bisect GCC to find out whether or not that was
intentional. At any rate, isn't this the proper fix? I can send it as a
formal patch if desired.

Cheers,
Nathan

diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
index db85df1d5073..067d4c2f7bf4 100644
--- a/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
+++ b/drivers/vdpa/vdpa_sim/vdpa_sim_blk.c
@@ -197,7 +197,7 @@ static bool vdpasim_blk_handle_req(struct vdpasim *vdpasim,
 		break;
 
 	case VIRTIO_BLK_T_DISCARD:
-	case VIRTIO_BLK_T_WRITE_ZEROES:
+	case VIRTIO_BLK_T_WRITE_ZEROES: {
 		struct virtio_blk_discard_write_zeroes range;
 		u32 num_sectors, flags;
 
@@ -253,6 +253,7 @@ static bool vdpasim_blk_handle_req(struct vdpasim *vdpasim,
 		}
 
 		break;
+	}
 
 	default:
 		dev_dbg(&vdpasim->vdpa.dev,