Use snprintf rather than double strncpy.

yjit_iface.c

@@ -766,10 +766,9 @@ get_yjit_stats(rb_execution_context_t *ec, VALUE self)
         // where the value is the count of side exits for that instruction.
 
         char key_string[rb_vm_max_insn_name_size + 6]; // Leave room for "exit_" and a final NUL
-        strncpy(key_string, "exit_", 6);               // Copy 6 characters to include the NUL.
         for (int i = 0; i < VM_INSTRUCTION_SIZE; i++) {
             const char *i_name = insn_name(i); // Look up Ruby's NUL-terminated insn name string
-            strncpy(key_string + 5, i_name, rb_vm_max_insn_name_size + 1);
+            snprintf(key_string, rb_vm_max_insn_name_size + 6, "%s%s", "exit_", i_name);
 
             VALUE key = ID2SYM(rb_intern(key_string));
             VALUE value = LL2NUM((long long)exit_op_count[i]);