fix multiboot loading if load_end_addr == 0

The previous multiboot load code did not treat the case where
load_end_addr was 0 specially.  The multiboot specification says the
following:
 * load_end_addr
   Contains the physical address of the end of the data segment.
   (load_end_addr - load_addr) specifies how much data to load. This
   implies that the text and data segments must be consecutive in the
   OS image; this is true for existing a.out executable formats. If
   this field is zero, the boot loader assumes that the text and data
   segments occupy the whole OS image file.
Signed-off-by: NScott Moser <smoser@ubuntu.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/multiboot.c

@@ -202,10 +202,16 @@ int load_multiboot(void *fw_cfg,
         uint32_t mh_bss_end_addr = ldl_p(header+i+24);
         mh_load_addr = ldl_p(header+i+16);
         uint32_t mb_kernel_text_offset = i - (mh_header_addr - mh_load_addr);
-        uint32_t mb_load_size = mh_load_end_addr - mh_load_addr;
-
+        uint32_t mb_load_size = 0;
         mh_entry_addr = ldl_p(header+i+28);
-        mb_kernel_size = mh_bss_end_addr - mh_load_addr;
+
+        if (mh_load_end_addr) {
+            mb_kernel_size = mh_bss_end_addr - mh_load_addr;
+            mb_load_size = mh_load_end_addr - mh_load_addr;
+        } else {
+            mb_kernel_size = kernel_file_size - mb_kernel_text_offset;
+            mb_load_size = mb_kernel_size;
+        }
 
         /* Valid if mh_flags sets MULTIBOOT_HEADER_HAS_VBE.
         uint32_t mh_mode_type = ldl_p(header+i+32);