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[88.21.205.47]) by smtp.gmail.com with ESMTPSA id d13sm1448784edk.0.2020.03.04.01.00.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 04 Mar 2020 01:00:36 -0800 (PST) Subject: Re: [PATCH 2/2] misc: Replace zero-length arrays with flexible array member (manual) To: qemu-devel@nongnu.org References: <20200304005105.27454-1-philmd@redhat.com> <20200304005844.28346-1-philmd@redhat.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: <00f90dff-cf19-6b6f-f245-d332df58107b@redhat.com> Date: Wed, 4 Mar 2020 10:00:33 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200304005844.28346-1-philmd@redhat.com> Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Fam Zheng , Peter Maydell , "Michael S. Tsirkin" , Jason Wang , Yuval Shaia , Gerd Hoffmann , Stefano Stabellini , qemu-block@nongnu.org, David Hildenbrand , "Gustavo A . R . Silva" , Halil Pasic , Christian Borntraeger , "Gonglei \(Arei\)" , Anthony Perard , xen-devel@lists.xenproject.org, Thomas Huth , Eduardo Habkost , Paul Durrant , Eric Auger , qemu-s390x@nongnu.org, qemu-arm@nongnu.org, =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= , John Snow , Richard Henderson , Kevin Wolf , Xiao Guangrong , Cornelia Huck , Laurent Vivier , Max Reitz , Igor Mammedov , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 3/4/20 1:58 AM, Philippe Mathieu-Daud=C3=A9 wrote: > Description copied from Linux kernel commit from Gustavo A. R. Silva > (see [3]): >=20 > --v-- description start --v-- >=20 > The current codebase makes use of the zero-length array language > extension to the C90 standard, but the preferred mechanism to > declare variable-length types such as these ones is a flexible > array member [1], introduced in C99: >=20 > struct foo { > int stuff; > struct boo array[]; > }; >=20 > By making use of the mechanism above, we will get a compiler > warning in case the flexible array does not occur last in the > structure, which will help us prevent some kind of undefined > behavior bugs from being unadvertenly introduced [2] to the > Linux codebase from now on. >=20 > --^-- description end --^-- >=20 > Do the similar housekeeping in the QEMU codebase (which uses > C99 since commit 7be41675f7cb). >=20 > All these instances of code were found with the help of the > following command (then manual analysis): >=20 > git grep -F '[0];' >=20 > [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html > [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/co= mmit/?id=3D76497732932f > [3] https://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux.git/= commit/?id=3D17642a2fbd2c1 >=20 > Inspired-by: Gustavo A. R. Silva > Signed-off-by: Philippe Mathieu-Daud=C3=A9 > --- > docs/interop/vhost-user.rst | 4 ++-- > block/qed.h | 2 +- > include/hw/acpi/acpi-defs.h | 4 ++-- > include/hw/boards.h | 2 +- > include/hw/s390x/event-facility.h | 2 +- > include/hw/s390x/sclp.h | 8 ++++---- > block/vmdk.c | 2 +- > hw/char/sclpconsole-lm.c | 2 +- > hw/char/sclpconsole.c | 2 +- > hw/s390x/virtio-ccw.c | 2 +- > target/s390x/ioinst.c | 2 +- > 11 files changed, 16 insertions(+), 16 deletions(-) >=20 > diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst > index 401652397c..3b1b6602c7 100644 > --- a/docs/interop/vhost-user.rst > +++ b/docs/interop/vhost-user.rst > @@ -568,7 +568,7 @@ For split virtqueue, queue region can be implemented = as: > uint16_t used_idx; > =20 > /* Used to track the state of each descriptor in descriptor table= */ > - DescStateSplit desc[0]; > + DescStateSplit desc[]; > } QueueRegionSplit; > =20 > To track inflight I/O, the queue region should be processed as follows: > @@ -690,7 +690,7 @@ For packed virtqueue, queue region can be implemented= as: > uint8_t padding[7]; > =20 > /* Used to track the state of each descriptor fetched from descri= ptor ring */ > - DescStatePacked desc[0]; > + DescStatePacked desc[]; > } QueueRegionPacked; > =20 > To track inflight I/O, the queue region should be processed as follows: > diff --git a/block/qed.h b/block/qed.h > index 42c115d822..87428ba00e 100644 > --- a/block/qed.h > +++ b/block/qed.h > @@ -103,7 +103,7 @@ typedef struct { > } QEMU_PACKED QEDHeader; > =20 > typedef struct { > - uint64_t offsets[0]; /* in bytes */ > + uint64_t offsets[]; /* in bytes */ Apparently this one is incorrect, it triggers: GCC: block/qed.h:106:14: error: flexible array member in otherwise empty struct Clang: block/qed.h:106:14: error: flexible array member 'offsets' not allowed=20 in otherwise empty struct > } QEDTable; > =20 > /* The L2 cache is a simple write-through cache for L2 structures */ > diff --git a/include/hw/acpi/acpi-defs.h b/include/hw/acpi/acpi-defs.h > index 19f7ba7b70..c13327fa78 100644 > --- a/include/hw/acpi/acpi-defs.h > +++ b/include/hw/acpi/acpi-defs.h > @@ -152,7 +152,7 @@ typedef struct AcpiSerialPortConsoleRedirection > */ > struct AcpiRsdtDescriptorRev1 { > ACPI_TABLE_HEADER_DEF /* ACPI common table header */ > - uint32_t table_offset_entry[0]; /* Array of pointers to other */ > + uint32_t table_offset_entry[]; /* Array of pointers to other */ > /* ACPI tables */ > } QEMU_PACKED; > typedef struct AcpiRsdtDescriptorRev1 AcpiRsdtDescriptorRev1; > @@ -162,7 +162,7 @@ typedef struct AcpiRsdtDescriptorRev1 AcpiRsdtDescrip= torRev1; > */ > struct AcpiXsdtDescriptorRev2 { > ACPI_TABLE_HEADER_DEF /* ACPI common table header */ > - uint64_t table_offset_entry[0]; /* Array of pointers to other */ > + uint64_t table_offset_entry[]; /* Array of pointers to other */ > /* ACPI tables */ > } QEMU_PACKED; > typedef struct AcpiXsdtDescriptorRev2 AcpiXsdtDescriptorRev2; > diff --git a/include/hw/boards.h b/include/hw/boards.h > index 9bc42dfb22..c96120d15f 100644 > --- a/include/hw/boards.h > +++ b/include/hw/boards.h > @@ -71,7 +71,7 @@ typedef struct CPUArchId { > */ > typedef struct { > int len; > - CPUArchId cpus[0]; > + CPUArchId cpus[]; > } CPUArchIdList; > =20 > /** > diff --git a/include/hw/s390x/event-facility.h b/include/hw/s390x/event-f= acility.h > index bdc32a3c09..700a610f33 100644 > --- a/include/hw/s390x/event-facility.h > +++ b/include/hw/s390x/event-facility.h > @@ -122,7 +122,7 @@ typedef struct MDBO { > =20 > typedef struct MDB { > MdbHeader header; > - MDBO mdbo[0]; > + MDBO mdbo[]; > } QEMU_PACKED MDB; > =20 > typedef struct SclpMsg { > diff --git a/include/hw/s390x/sclp.h b/include/hw/s390x/sclp.h > index c54413b78c..cd7b24359f 100644 > --- a/include/hw/s390x/sclp.h > +++ b/include/hw/s390x/sclp.h > @@ -132,7 +132,7 @@ typedef struct ReadInfo { > uint16_t highest_cpu; > uint8_t _reserved5[124 - 122]; /* 122-123 */ > uint32_t hmfai; > - struct CPUEntry entries[0]; > + struct CPUEntry entries[]; > } QEMU_PACKED ReadInfo; > =20 > typedef struct ReadCpuInfo { > @@ -142,7 +142,7 @@ typedef struct ReadCpuInfo { > uint16_t nr_standby; /* 12-13 */ > uint16_t offset_standby; /* 14-15 */ > uint8_t reserved0[24-16]; /* 16-23 */ > - struct CPUEntry entries[0]; > + struct CPUEntry entries[]; > } QEMU_PACKED ReadCpuInfo; > =20 > typedef struct ReadStorageElementInfo { > @@ -151,7 +151,7 @@ typedef struct ReadStorageElementInfo { > uint16_t assigned; > uint16_t standby; > uint8_t _reserved0[16 - 14]; /* 14-15 */ > - uint32_t entries[0]; > + uint32_t entries[]; > } QEMU_PACKED ReadStorageElementInfo; > =20 > typedef struct AttachStorageElement { > @@ -159,7 +159,7 @@ typedef struct AttachStorageElement { > uint8_t _reserved0[10 - 8]; /* 8-9 */ > uint16_t assigned; > uint8_t _reserved1[16 - 12]; /* 12-15 */ > - uint32_t entries[0]; > + uint32_t entries[]; > } QEMU_PACKED AttachStorageElement; > =20 > typedef struct AssignStorage { > diff --git a/block/vmdk.c b/block/vmdk.c > index 20e909d997..8466051bc9 100644 > --- a/block/vmdk.c > +++ b/block/vmdk.c > @@ -187,7 +187,7 @@ typedef struct VmdkMetaData { > typedef struct VmdkGrainMarker { > uint64_t lba; > uint32_t size; > - uint8_t data[0]; > + uint8_t data[]; > } QEMU_PACKED VmdkGrainMarker; > =20 > enum { > diff --git a/hw/char/sclpconsole-lm.c b/hw/char/sclpconsole-lm.c > index c420dc066e..2b5f37b6a2 100644 > --- a/hw/char/sclpconsole-lm.c > +++ b/hw/char/sclpconsole-lm.c > @@ -31,7 +31,7 @@ > typedef struct OprtnsCommand { > EventBufferHeader header; > MDMSU message_unit; > - char data[0]; > + char data[]; > } QEMU_PACKED OprtnsCommand; > =20 > /* max size for line-mode data in 4K SCCB page */ > diff --git a/hw/char/sclpconsole.c b/hw/char/sclpconsole.c > index 1fa124dab9..5c7664905e 100644 > --- a/hw/char/sclpconsole.c > +++ b/hw/char/sclpconsole.c > @@ -25,7 +25,7 @@ > =20 > typedef struct ASCIIConsoleData { > EventBufferHeader ebh; > - char data[0]; > + char data[]; > } QEMU_PACKED ASCIIConsoleData; > =20 > /* max size for ASCII data in 4K SCCB page */ > diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c > index 50cf95b781..64f928fc7d 100644 > --- a/hw/s390x/virtio-ccw.c > +++ b/hw/s390x/virtio-ccw.c > @@ -193,7 +193,7 @@ typedef struct VirtioThinintInfo { > typedef struct VirtioRevInfo { > uint16_t revision; > uint16_t length; > - uint8_t data[0]; > + uint8_t data[]; > } QEMU_PACKED VirtioRevInfo; > =20 > /* Specify where the virtqueues for the subchannel are in guest memory.= */ > diff --git a/target/s390x/ioinst.c b/target/s390x/ioinst.c > index c437a1d8c6..0e840cc579 100644 > --- a/target/s390x/ioinst.c > +++ b/target/s390x/ioinst.c > @@ -347,7 +347,7 @@ typedef struct ChscResp { > uint16_t len; > uint16_t code; > uint32_t param; > - char data[0]; > + char data[]; > } QEMU_PACKED ChscResp; > =20 > #define CHSC_MIN_RESP_LEN 0x0008 >=20