multiboot: Fix offset of bootloader name

This fixes a bug introduced in commit 5eba5a66 ('Add bootloader name to
multiboot implementation').

The calculation of the bootloader name offset didn't consider space
occupied by module command lines, so some unlucky module got its command
line partially overwritten with a "qemu" string.
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

hw/i386/multiboot.c

@@ -156,6 +156,7 @@ int load_multiboot(FWCfgState *fw_cfg,
     MultibootState mbs;
     uint8_t bootinfo[MBI_SIZE];
     uint8_t *mb_bootinfo_data;
+    uint32_t cmdline_len;
 
     /* Ok, let's see if it is a multiboot image.
        The header is 12x32bit long, so the latest entry may be 8192 - 48. */
@@ -258,27 +259,28 @@ int load_multiboot(FWCfgState *fw_cfg,
     mbs.offset_mbinfo = mbs.mb_buf_size;
 
     /* Calculate space for cmdlines, bootloader name, and mb_mods */
-    mbs.mb_buf_size += strlen(kernel_filename) + 1;
-    mbs.mb_buf_size += strlen(kernel_cmdline) + 1;
-    mbs.mb_buf_size += strlen(bootloader_name) + 1;
+    cmdline_len = strlen(kernel_filename) + 1;
+    cmdline_len += strlen(kernel_cmdline) + 1;
     if (initrd_filename) {
         const char *r = initrd_filename;
-        mbs.mb_buf_size += strlen(r) + 1;
+        cmdline_len += strlen(r) + 1;
         mbs.mb_mods_avail = 1;
         while (*(r = get_opt_value(NULL, 0, r))) {
            mbs.mb_mods_avail++;
            r++;
         }
-        mbs.mb_buf_size += MB_MOD_SIZE * mbs.mb_mods_avail;
     }
 
+    mbs.mb_buf_size += cmdline_len;
+    mbs.mb_buf_size += MB_MOD_SIZE * mbs.mb_mods_avail;
+    mbs.mb_buf_size += strlen(bootloader_name) + 1;
+
     mbs.mb_buf_size = TARGET_PAGE_ALIGN(mbs.mb_buf_size);
 
     /* enlarge mb_buf to hold cmdlines, bootloader, mb-info structs */
     mbs.mb_buf            = g_realloc(mbs.mb_buf, mbs.mb_buf_size);
     mbs.offset_cmdlines   = mbs.offset_mbinfo + mbs.mb_mods_avail * MB_MOD_SIZE;
-    mbs.offset_bootloader = mbs.offset_cmdlines + strlen(kernel_filename) + 1 
-                            + strlen(kernel_cmdline) + 1;
+    mbs.offset_bootloader = mbs.offset_cmdlines + cmdline_len;
 
     if (initrd_filename) {
         char *next_initrd, not_last;