sparc: Replace one-element array with flexible array member

Replace the deprecated one-element array with a modern flexible array
member in the struct hvtramp_descr.

Additionally, 15 unnecessary bytes were allocated for hdesc, but instead
of fixing the parentheses in the open-coded version, use struct_size()
to calculate the correct number of bytes.

Link: KSPP/linux#79
Signed-off-by: Thorsten Blum <[email protected]>
Fixes: 6465874 ("[SPARC64]: Remove most limitations to kernel image size.")
Reviewed-by: Andreas Larsson <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Andreas Larsson <[email protected]>

Author: toblux

arch/sparc/include/asm/hvtramp.h

@@ -17,7 +17,7 @@ struct hvtramp_descr {
 	__u64			fault_info_va;
 	__u64			fault_info_pa;
 	__u64			thread_reg;
-	struct hvtramp_mapping	maps[1];
+	struct hvtramp_mapping	maps[];
 };
 
 void hv_cpu_startup(unsigned long hvdescr_pa);

arch/sparc/kernel/smp_64.c

@@ -297,9 +297,7 @@ static void ldom_startcpu_cpuid(unsigned int cpu, unsigned long thread_reg,
 	unsigned long hv_err;
 	int i;
 
-	hdesc = kzalloc(sizeof(*hdesc) +
-			(sizeof(struct hvtramp_mapping) *
-			 num_kernel_image_mappings - 1),
+	hdesc = kzalloc(struct_size(hdesc, maps, num_kernel_image_mappings),
 			GFP_KERNEL);
 	if (!hdesc) {
 		printk(KERN_ERR "ldom_startcpu_cpuid: Cannot allocate "