[multiboot] Build memory map after shutting down and unhiding gPXE

The Multiboot memory map needs to be built after unhiding gPXE and
downloaded images from memory.  Solaris faults during boot when trying
to access the ramdisk, which is hidden from the memory map while gPXE is
executing.  This issue is fixed by using the memory map from after gPXE
unhides itself.

Reported-by: Moinak Ghosh <moinakg@belenix.org>
Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>

src/arch/i386/image/multiboot.c

@@ -267,8 +267,6 @@ static int multiboot_exec ( struct image *image ) {
 	memset ( &mbinfo, 0, sizeof ( mbinfo ) );
 	mbinfo.flags = ( MBI_FLAG_LOADER | MBI_FLAG_MEM | MBI_FLAG_MMAP |
 			 MBI_FLAG_CMDLINE | MBI_FLAG_MODS );
-	multiboot_build_memmap ( image, &mbinfo, mbmemmap,
-				 ( sizeof(mbmemmap) / sizeof(mbmemmap[0]) ) );
 	mb_cmdline_offset = 0;
 	mbinfo.cmdline = multiboot_add_cmdline ( image->name, image->cmdline );
 	mbinfo.mods_count = multiboot_build_module_list ( image, mbmodules,
@@ -282,6 +280,12 @@ static int multiboot_exec ( struct image *image ) {
 	 */
 	shutdown ( SHUTDOWN_BOOT );
 
+	/* Build memory map after unhiding bootloader memory regions as part of
+	 * shutting everything down.
+	 */
+	multiboot_build_memmap ( image, &mbinfo, mbmemmap,
+				 ( sizeof(mbmemmap) / sizeof(mbmemmap[0]) ) );
+
 	/* Jump to OS with flat physical addressing */
 	DBGC ( image, "MULTIBOOT %p starting execution at %lx\n",
 	       image, entry );