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, 3 insertions, 3 deletions

diff --git a/arch/s390/include/uapi/asm/hwctrset.h b/arch/s390/include/uapi/asm/hwctrset.h
index 3d8284b95f87..e56b9dd23a4b 100644
--- a/arch/s390/include/uapi/asm/hwctrset.h
+++ b/arch/s390/include/uapi/asm/hwctrset.h
@@ -30,18 +30,18 @@ struct s390_ctrset_start {		/* Set CPUs to operate on */
 struct s390_ctrset_setdata {		/* Counter set data */
 	__u32 set;			/* Counter set number */
 	__u32 no_cnts;			/* # of counters stored in cv[] */
-	__u64 cv[0];			/* Counter values (variable length) */
+	__u64 cv[];			/* Counter values (variable length) */
 };
 
 struct s390_ctrset_cpudata {		/* Counter set data per CPU */
 	__u32 cpu_nr;			/* CPU number */
 	__u32 no_sets;			/* # of counters sets in data[] */
-	struct s390_ctrset_setdata data[0];
+	struct s390_ctrset_setdata data[];
 };
 
 struct s390_ctrset_read {		/* Structure to get all ctr sets */
 	__u64 no_cpus;			/* Total # of CPUs data taken from */
-	struct s390_ctrset_cpudata data[0];
+	struct s390_ctrset_cpudata data[];
 };
 
 #define S390_HWCTR_MAGIC	'C'	/* Random magic # for ioctls */