Workaround UBSAN errors for variable arrays

This gets around UBSAN errors when using arrays at the end of
structs.  It converts some zero-length arrays to variable length
arrays and disables UBSAN checking on certain modules.

It is based off of the patch from openzfs#15460.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Tested-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Co-authored-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Issue openzfs#15145
Closes openzfs#15510

include/os/linux/spl/sys/kmem_cache.h

@@ -111,7 +111,7 @@ typedef struct spl_kmem_magazine {
 	uint32_t		skm_refill;	/* Batch refill size */
 	struct spl_kmem_cache	*skm_cache;	/* Owned by cache */
 	unsigned int		skm_cpu;	/* Owned by cpu */
-	void			*skm_objs[0];	/* Object pointers */
+	void			*skm_objs[];	/* Object pointers */
 } spl_kmem_magazine_t;
 
 typedef struct spl_kmem_obj {

include/sys/vdev_raidz_impl.h

@@ -130,7 +130,7 @@ typedef struct raidz_row {
 	uint64_t rr_offset;		/* Logical offset for *_io_verify() */
 	uint64_t rr_size;		/* Physical size for *_io_verify() */
 #endif
-	raidz_col_t rr_col[0];		/* Flexible array of I/O columns */
+	raidz_col_t rr_col[];		/* Flexible array of I/O columns */
 } raidz_row_t;
 
 typedef struct raidz_map {
@@ -139,7 +139,7 @@ typedef struct raidz_map {
 	int rm_nskip;			/* RAIDZ sectors skipped for padding */
 	int rm_skipstart;		/* Column index of padding start */
 	const raidz_impl_ops_t *rm_ops;	/* RAIDZ math operations */
-	raidz_row_t *rm_row[0];		/* flexible array of rows */
+	raidz_row_t *rm_row[];		/* flexible array of rows */
 } raidz_map_t;
 
 

module/zfs/Makefile.in

@@ -159,4 +159,8 @@ CFLAGS_REMOVE_vdev_raidz_math_aarch64_neon.o += -mgeneral-regs-only
 CFLAGS_REMOVE_vdev_raidz_math_aarch64_neonx2.o += -mgeneral-regs-only
 endif
 
+UBSAN_SANITIZE_zap_leaf.o := n
+UBSAN_SANITIZE_zap_micro.o := n
+UBSAN_SANITIZE_sa.o := n
+
 include $(mfdir)/../os/linux/zfs/Makefile