diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index e22ab47..f9d5cf0 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -507,10 +507,10 @@
 extern void perf_counter_munmap(unsigned long addr, unsigned long len,
 				unsigned long pgoff, struct file *file);
 
-#define MAX_STACK_DEPTH		254
+#define MAX_STACK_DEPTH		255
 
 struct perf_callchain_entry {
-	u32	nr, hv, kernel, user;
+	u16	nr, hv, kernel, user;
 	u64	ip[MAX_STACK_DEPTH];
 };
 
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 2a5d4f5..727624d 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -1657,9 +1657,7 @@
  * Callchain support -- arch specific
  */
 
-struct perf_callchain_entry *
-__attribute__((weak))
-perf_callchain(struct pt_regs *regs)
+__weak struct perf_callchain_entry *perf_callchain(struct pt_regs *regs)
 {
 	return NULL;
 }
@@ -1819,7 +1817,7 @@
 		callchain = perf_callchain(regs);
 
 		if (callchain) {
-			callchain_size = (2 + callchain->nr) * sizeof(u64);
+			callchain_size = (1 + callchain->nr) * sizeof(u64);
 
 			header.type |= __PERF_EVENT_CALLCHAIN;
 			header.size += callchain_size;