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

On Thu, Aug 11, 2022 at 11:31:21AM -0700, Nathan Chancellor wrote:

On Thu, Aug 11, 2022 at 06:22:54PM +0100, Sudip Mukherjee (Codethink) wrote:

quoted

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

Interesting, I confirm that also gcc 12 does not warns/error.
This is my version:

     $ gcc --version
     gcc (GCC) 12.1.1 20220507 (Red Hat 12.1.1-1)

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.

Yep, that was the fix and I already re-sent a new series with the patch
fixed:
https://lore.kernel.org/virtualization/20220811083632.77525-1-sgarzare@redhat.com/T/#t (local)

Michael already queued the new version in his tree:
https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git linux-next

Thanks,
Stefano

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