x86: add multiboot2 protocol support for relocatable images

Add multiboot2 protocol support for relocatable images. Only GRUB2 with
"multiboot2: Add support for relocatable images" patch understands
that feature. Older multiboot protocol (regardless of version)
compatible loaders ignore it and everything works as usual.

Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Doug Goldstein <cardoe@cardoe.com>

xen/arch/x86/boot/head.S

@@ -81,6 +81,13 @@ multiboot2_header_start:
         /* Align modules at page boundry. */
         mb2ht_init MB2_HT(MODULE_ALIGN), MB2_HT(REQUIRED)
 
+        /* Load address preference. */
+        mb2ht_init MB2_HT(RELOCATABLE), MB2_HT(OPTIONAL), \
+                   sym_offs(start), /* Min load address. */ \
+                   0xffffffff, /* The end of image max load address (4 GiB - 1). */ \
+                   0x200000, /* Load address alignment (2 MiB). */ \
+                   MULTIBOOT2_LOAD_PREFERENCE_HIGH
+
         /* Console flags tag. */
         mb2ht_init MB2_HT(CONSOLE_FLAGS), MB2_HT(OPTIONAL), \
                    MULTIBOOT2_CONSOLE_FLAGS_EGA_TEXT_SUPPORTED
@@ -403,6 +410,15 @@ __start:
         cmp     %edi,MB2_fixed_total_size(%ebx)
         jbe     trampoline_bios_setup
 
+        /* Get Xen image load base address from Multiboot2 information. */
+        cmpl    $MULTIBOOT2_TAG_TYPE_LOAD_BASE_ADDR,MB2_tag_type(%ecx)
+        jne     .Lmb2_mem_lower
+
+        mov     MB2_load_base_addr(%ecx),%esi
+        sub     $XEN_IMG_OFFSET,%esi
+        jmp     .Lmb2_next_tag
+
+.Lmb2_mem_lower:
         /* Get mem_lower from Multiboot2 information. */
         cmpl    $MULTIBOOT2_TAG_TYPE_BASIC_MEMINFO,MB2_tag_type(%ecx)
         cmove   MB2_mem_lower(%ecx),%edx

xen/arch/x86/x86_64/asm-offsets.c

@@ -173,6 +173,7 @@ void __dummy__(void)
     OFFSET(MB2_fixed_total_size, multiboot2_fixed_t, total_size);
     OFFSET(MB2_tag_type, multiboot2_tag_t, type);
     OFFSET(MB2_tag_size, multiboot2_tag_t, size);
+    OFFSET(MB2_load_base_addr, multiboot2_tag_load_base_addr_t, load_base_addr);
     OFFSET(MB2_mem_lower, multiboot2_tag_basic_meminfo_t, mem_lower);
     OFFSET(MB2_efi64_st, multiboot2_tag_efi64_t, pointer);
     OFFSET(MB2_efi64_ih, multiboot2_tag_efi64_ih_t, pointer);

xen/include/xen/multiboot2.h

@@ -59,11 +59,17 @@
 #define MULTIBOOT2_HEADER_TAG_EFI_BS                    7
 #define MULTIBOOT2_HEADER_TAG_ENTRY_ADDRESS_EFI32       8
 #define MULTIBOOT2_HEADER_TAG_ENTRY_ADDRESS_EFI64       9
+#define MULTIBOOT2_HEADER_TAG_RELOCATABLE               10
 
 /* Header tag flags. */
 #define MULTIBOOT2_HEADER_TAG_REQUIRED                  0
 #define MULTIBOOT2_HEADER_TAG_OPTIONAL                  1
 
+/* Where image should be loaded (suggestion not requirement). */
+#define MULTIBOOT2_LOAD_PREFERENCE_NONE                 0
+#define MULTIBOOT2_LOAD_PREFERENCE_LOW                  1
+#define MULTIBOOT2_LOAD_PREFERENCE_HIGH                 2
+
 /* Header console tag console_flags. */
 #define MULTIBOOT2_CONSOLE_FLAGS_CONSOLE_REQUIRED       1
 #define MULTIBOOT2_CONSOLE_FLAGS_EGA_TEXT_SUPPORTED     2
@@ -90,6 +96,7 @@
 #define MULTIBOOT2_TAG_TYPE_EFI_BS                      18
 #define MULTIBOOT2_TAG_TYPE_EFI32_IH                    19
 #define MULTIBOOT2_TAG_TYPE_EFI64_IH                    20
+#define MULTIBOOT2_TAG_TYPE_LOAD_BASE_ADDR              21
 
 /* Multiboot 2 tag alignment. */
 #define MULTIBOOT2_TAG_ALIGN                            8
@@ -117,6 +124,12 @@ typedef struct {
     u32 size;
 } multiboot2_tag_t;
 
+typedef struct {
+    u32 type;
+    u32 size;
+    u32 load_base_addr;
+} multiboot2_tag_load_base_addr_t;
+
 typedef struct {
     u32 type;
     u32 size;