[PATCH] usb: Fix clang build

[PATCH] usb: Fix clang build

[Eric Blake]

../hw/usb/dev-uas.c:157:31: error: field 'status' with variable sized type 'uas_iu' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end]
    uas_iu                    status;
                              ^

Fix this by specifying a size for the add_cdb member; and at present,
the code does not actually use that field other than for the size
chosen for the packed uas_iu_command struct, and the choice of one
byte does not change the size of the uas_iu union.

Signed-off-by: Eric Blake <eblake@redhat.com>
---

I'm not sure why none of our CI tools pick up this particular clang
build failure; I hit it on Fedora 33 when configuring to build the
entire tree with clang.

 hw/usb/dev-uas.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/usb/dev-uas.c b/hw/usb/dev-uas.c
index cec071d96c49..904d6ffa2938 100644
--- a/hw/usb/dev-uas.c
+++ b/hw/usb/dev-uas.c
@@ -70,7 +70,7 @@ typedef struct {
     uint8_t    reserved_2;
     uint64_t   lun;
     uint8_t    cdb[16];
-    uint8_t    add_cdb[];
+    uint8_t    add_cdb[1];
 } QEMU_PACKED  uas_iu_command;

 typedef struct {
-- 
2.30.0

Re: [PATCH] usb: Fix clang build

[Philippe Mathieu-Daudé]

Hi Eric,

On 1/20/21 12:07 AM, Eric Blake wrote:
> ../hw/usb/dev-uas.c:157:31: error: field 'status' with variable sized type 'uas_iu' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end]
>     uas_iu                    status;
>                               ^
> 
> Fix this by specifying a size for the add_cdb member; and at present,
> the code does not actually use that field other than for the size
> chosen for the packed uas_iu_command struct, and the choice of one
> byte does not change the size of the uas_iu union.

I sent a maybe safer approach (from the bus PoV):
https://www.mail-archive.com/qemu-block@nongnu.org/msg79192.html

Do you mind reviewing it?

> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---
> 
> I'm not sure why none of our CI tools pick up this particular clang
> build failure; I hit it on Fedora 33 when configuring to build the
> entire tree with clang.

Same issue after upgrading to f33. I sent a patch to bump our CI:
https://www.mail-archive.com/qemu-devel@nongnu.org/msg774117.html

To track Fedora releases I was thinking about a gitlab job checking
if we are using the latest, else failing; smth as:

 $ curl https://getfedora.org/ | grep -q 'Fedora 33 released'

Re: [PATCH] usb: Fix clang build

[Philippe Mathieu-Daudé]

On 1/20/21 12:20 AM, Philippe Mathieu-Daudé wrote:
> Hi Eric,
> 
> On 1/20/21 12:07 AM, Eric Blake wrote:
>> ../hw/usb/dev-uas.c:157:31: error: field 'status' with variable sized type 'uas_iu' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end]
>>     uas_iu                    status;
>>                               ^
>>
>> Fix this by specifying a size for the add_cdb member; and at present,
>> the code does not actually use that field other than for the size
>> chosen for the packed uas_iu_command struct, and the choice of one
>> byte does not change the size of the uas_iu union.
> 
> I sent a maybe safer approach (from the bus PoV):
> https://www.mail-archive.com/qemu-block@nongnu.org/msg79192.html
> 
> Do you mind reviewing it?
> 
>>
>> Signed-off-by: Eric Blake <eblake@redhat.com>
>> ---
>>
>> I'm not sure why none of our CI tools pick up this particular clang
>> build failure; I hit it on Fedora 33 when configuring to build the
>> entire tree with clang.

BTW first report is from 28 Sep 2020 (Ed):
https://www.mail-archive.com/qemu-devel@nongnu.org/msg745525.html

Then on 23 Oct 2020 (Daniele):
https://www.mail-archive.com/qemu-devel@nongnu.org/msg753674.html

Then on 10 Nov 2020 (Han):
https://www.mail-archive.com/qemu-devel@nongnu.org/msg759108.html

> Same issue after upgrading to f33. I sent a patch to bump our CI:
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg774117.html
> 
> To track Fedora releases I was thinking about a gitlab job checking
> if we are using the latest, else failing; smth as:
> 
>  $ curl https://getfedora.org/ | grep -q 'Fedora 33 released'
> 

Re: [PATCH] usb: Fix clang build

[Daniel P. Berrangé]

On Wed, Jan 20, 2021 at 12:20:43AM +0100, Philippe Mathieu-Daudé wrote:
> Hi Eric,
> 
> On 1/20/21 12:07 AM, Eric Blake wrote:
> > ../hw/usb/dev-uas.c:157:31: error: field 'status' with variable sized type 'uas_iu' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end]
> >     uas_iu                    status;
> >                               ^
> > 
> > Fix this by specifying a size for the add_cdb member; and at present,
> > the code does not actually use that field other than for the size
> > chosen for the packed uas_iu_command struct, and the choice of one
> > byte does not change the size of the uas_iu union.
> 
> I sent a maybe safer approach (from the bus PoV):
> https://www.mail-archive.com/qemu-block@nongnu.org/msg79192.html
> 
> Do you mind reviewing it?
> 
> > 
> > Signed-off-by: Eric Blake <eblake@redhat.com>
> > ---
> > 
> > I'm not sure why none of our CI tools pick up this particular clang
> > build failure; I hit it on Fedora 33 when configuring to build the
> > entire tree with clang.
> 
> Same issue after upgrading to f33. I sent a patch to bump our CI:
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg774117.html
> 
> To track Fedora releases I was thinking about a gitlab job checking
> if we are using the latest, else failing; smth as:
> 
>  $ curl https://getfedora.org/ | grep -q 'Fedora 33 released'

We'd be better off just adding a job that targets Fedora rawhide IMHO so
we get immediate notice that a toolchain update is going to hurt us, instead
of waiting until the next Fedora is already released to find the problem.


Regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|