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

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Message-ID: <20220811185008.jiqcv4ovv4sglsap@sgarzare-redhat>
Date:   Thu, 11 Aug 2022 20:50:08 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     "Sudip Mukherjee (Codethink)" <sudipm.mukherjee@...il.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        clang-built-linux <llvm@...ts.linux.dev>,
        linux-next@...r.kernel.org
Subject: 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:
>> 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

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