Re: [PATCH 2/2] misc: Replace zero-length arrays with flexible array member (manual)
On 3/4/20 1:58 AM, Philippe Mathieu-Daudé wrote:
Description copied from Linux kernel commit from Gustavo A. R. Silva
(see [3]):
--v-- description start --v--
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:
struct foo {
int stuff;
struct boo array[];
};
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.
--^-- description end --^--
Do the similar housekeeping in the QEMU codebase (which uses
C99 since commit 7be41675f7cb).
All these instances of code were found with the help of the
following command (then manual analysis):
git grep -F '[0];'
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=76497732932f
[3]
https://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux.git/commit/?id=17642a2fbd2c1
Inspired-by: Gustavo A. R. Silva
Signed-off-by: Philippe Mathieu-Daudé
---
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(-)
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;
/* Used to track the state of each descriptor in descriptor table */
- DescStateSplit desc[0];
+ DescStateSplit desc[];
} QueueRegionSplit;
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];
/* Used to track the state of each descriptor fetched from descriptor ring */
- DescStatePacked desc[0];
+ DescStatePacked desc[];
} QueueRegionPacked;
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;
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
in otherwise empty struct
} QEDTable;
/* 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
AcpiRsdtDescriptorRev1;
*/
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;
/**
diff --git a/include/hw/s390x/event-facility.h
b/include/hw/s390x/event-facility.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 {
typedef struct MDB {
Md
Re: [PATCH 2/2] misc: Replace zero-length arrays with flexible array member (manual)
On 04.03.20 01:58, Philippe Mathieu-Daudé wrote:
> Description copied from Linux kernel commit from Gustavo A. R. Silva
> (see [3]):
>
> --v-- description start --v--
>
> 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:
>
> struct foo {
> int stuff;
> struct boo array[];
> };
>
> 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.
>
> --^-- description end --^--
>
> Do the similar housekeeping in the QEMU codebase (which uses
> C99 since commit 7be41675f7cb).
>
> All these instances of code were found with the help of the
> following command (then manual analysis):
>
> git grep -F '[0];'
>
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [2]
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=76497732932f
> [3]
> https://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux.git/commit/?id=17642a2fbd2c1
>
> Inspired-by: Gustavo A. R. Silva
> Signed-off-by: Philippe Mathieu-Daudé
> ---
> 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(-)
>
> 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;
>
>/* Used to track the state of each descriptor in descriptor table */
> - DescStateSplit desc[0];
> + DescStateSplit desc[];
>} QueueRegionSplit;
>
> 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];
>
>/* Used to track the state of each descriptor fetched from descriptor
> ring */
> - DescStatePacked desc[0];
> + DescStatePacked desc[];
>} QueueRegionPacked;
>
> 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;
>
> typedef struct {
> -uint64_t offsets[0];/* in bytes */
> +uint64_t offsets[]; /* in bytes */
> } QEDTable;
>
> /* 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
> AcpiRsdtDescriptorRev1;
> */
> 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;
>
> /**
> diff --git a/include/hw/s390x/event-facility.h
> b/include/hw/s390x/event-facility.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 {
>
> typedef struct MDB {
> MdbHeader header;
> -MDBO mdbo[0];
> +M
