misc: Replace zero-length arrays with flexible array member (manual)

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 7be4167).

All these instances of code were found with the help of the
following command (then manual analysis, without modifying
structures only having a single flexible array member, such
QEDTable in block/qed.h):

  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 <gustavo@embeddedor.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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;
 
 enum {

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:

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;
 
 /* max size for line-mode data in 4K SCCB page */

hw/char/sclpconsole.c

@@ -25,7 +25,7 @@
 
 typedef struct ASCIIConsoleData {
     EventBufferHeader ebh;
-    char data[0];
+    char data[];
 } QEMU_PACKED ASCIIConsoleData;
 
 /* max size for ASCII data in 4K SCCB page */

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;
 
 /* Specify where the virtqueues for the subchannel are in guest memory. */

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;

include/hw/boards.h

@@ -71,7 +71,7 @@ typedef struct CPUArchId {
  */
 typedef struct {
     int len;
-    CPUArchId cpus[0];
+    CPUArchId cpus[];
 } CPUArchIdList;
 
 /**

include/hw/s390x/event-facility.h

@@ -122,7 +122,7 @@ typedef struct MDBO {
 
 typedef struct MDB {
     MdbHeader header;
-    MDBO mdbo[0];
+    MDBO mdbo[];
 } QEMU_PACKED MDB;
 
 typedef struct SclpMsg {

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;
 
 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;
 
 typedef struct ReadStorageElementInfo {
@@ -151,15 +151,15 @@ 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;
 
 typedef struct AttachStorageElement {
     SCCBHeader h;
     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;
 
 typedef struct AssignStorage {

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;
 
 #define CHSC_MIN_RESP_LEN 0x0008