treewide: uapi: Replace zero-length arrays with flexible-array members

There is a regular need in the kernel to provide a way to declare
having a dynamically sized set of trailing elements in a structure.
Kernel code should always use “flexible array members”[1] for these
cases. The older style of one-element or zero-length arrays should
no longer be used[2].

This code was transformed with the help of Coccinelle:
(linux-5.19-rc2$ spatch --jobs $(getconf _NPROCESSORS_ONLN) --sp-file script.cocci --include-headers --dir . > output.patch)

@@
identifier S, member, array;
type T1, T2;
@@

struct S {
  ...
  T1 member;
  T2 array[
- 0
  ];
};

-fstrict-flex-arrays=3 is coming and we need to land these changes
to prevent issues like these in the short future:

../fs/minix/dir.c:337:3: warning: 'strcpy' will always overflow; destination buffer has size 0,
but the source string has length 2 (including NUL byte) [-Wfortify-source]
		strcpy(de3->name, ".");
		^

Since these are all [0] to [] changes, the risk to UAPI is nearly zero. If
this breaks anything, we can use a union with a new member name.

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.16/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/78
Build-tested-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/lkml/62b675ec.wKX6AOZ6cbE71vtF%25lkp@intel.com/
Acked-by: Dan Williams <dan.j.williams@intel.com> # For ndctl.h
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

1 files changed, 6 insertions, 6 deletions

diff --git a/tools/arch/x86/include/uapi/asm/kvm.h b/tools/arch/x86/include/uapi/asm/kvm.h
index bf6e96011dfe..e135f4dcb19d 100644
--- a/tools/arch/x86/include/uapi/asm/kvm.h
+++ b/tools/arch/x86/include/uapi/asm/kvm.h
@@ -198,13 +198,13 @@ struct kvm_msrs {
 	__u32 nmsrs; /* number of msrs in entries */
 	__u32 pad;
 
-	struct kvm_msr_entry entries[0];
+	struct kvm_msr_entry entries[];
 };
 
 /* for KVM_GET_MSR_INDEX_LIST */
 struct kvm_msr_list {
 	__u32 nmsrs; /* number of msrs in entries */
-	__u32 indices[0];
+	__u32 indices[];
 };
 
 /* Maximum size of any access bitmap in bytes */
@@ -241,7 +241,7 @@ struct kvm_cpuid_entry {
 struct kvm_cpuid {
 	__u32 nent;
 	__u32 padding;
-	struct kvm_cpuid_entry entries[0];
+	struct kvm_cpuid_entry entries[];
 };
 
 struct kvm_cpuid_entry2 {
@@ -263,7 +263,7 @@ struct kvm_cpuid_entry2 {
 struct kvm_cpuid2 {
 	__u32 nent;
 	__u32 padding;
-	struct kvm_cpuid_entry2 entries[0];
+	struct kvm_cpuid_entry2 entries[];
 };
 
 /* for KVM_GET_PIT and KVM_SET_PIT */
@@ -389,7 +389,7 @@ struct kvm_xsave {
 	 * the contents of CPUID leaf 0xD on the host.
 	 */
 	__u32 region[1024];
-	__u32 extra[0];
+	__u32 extra[];
 };
 
 #define KVM_MAX_XCRS	16
@@ -515,7 +515,7 @@ struct kvm_pmu_event_filter {
 	__u32 fixed_counter_bitmap;
 	__u32 flags;
 	__u32 pad[4];
-	__u64 events[0];
+	__u64 events[];
 };
 
 #define KVM_PMU_EVENT_ALLOW 0