[Xen-devel] [PATCH v6 15/15] x86: add multiboot2 protocol support for relocatable images

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

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@xxxxxxxxxx>
---
v4 - suggestions/fixes:
   - do not get Xen image load base address from
     multiboot2 information in x86_64 code
     (suggested by Jan Beulich),
   - improve label names
     (suggested by Jan Beulich),
   - improve comments,
     (suggested by Jan Beulich).

v3 - suggestions/fixes:
   - use %esi and %r15d instead of %ebp to store
     Xen image load base address,
   - rename some types and constants,
   - reformat xen/include/xen/multiboot2.h
     (suggested by Konrad Rzeszutek Wilk),
   - improve comments,
   - improve commit message
     (suggested by Konrad Rzeszutek Wilk).
---
 xen/arch/x86/boot/head.S          |   19 ++++++++++++++++++-
 xen/arch/x86/x86_64/asm-offsets.c |    1 +
 xen/include/xen/multiboot2.h      |   13 +++++++++++++
 3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index bb2163a..9761d30 100644
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -82,6 +82,13 @@ 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
@@ -382,10 +389,19 @@ __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     1f
+
+        mov     MB2_load_base_addr(%ecx),%esi
+        sub     $XEN_IMG_OFFSET,%esi
+        jmp     9f
+
+1:
         /* Get mem_lower from Multiboot2 information. */
         cmpl    $MULTIBOOT2_TAG_TYPE_BASIC_MEMINFO,MB2_tag_type(%ecx)
         cmove   MB2_mem_lower(%ecx),%edx
-        je      trampoline_bios_setup
+        je      9f
 
         /* EFI IA-32 platforms are not supported. */
         cmpl    $MULTIBOOT2_TAG_TYPE_EFI32,MB2_tag_type(%ecx)
@@ -399,6 +415,7 @@ __start:
         cmpl    $MULTIBOOT2_TAG_TYPE_END,MB2_tag_type(%ecx)
         je      trampoline_bios_setup
 
+9:
         /* Go to next Multiboot2 information tag. */
         add     MB2_tag_size(%ecx),%ecx
         add     $(MULTIBOOT2_TAG_ALIGN-1),%ecx
diff --git a/xen/arch/x86/x86_64/asm-offsets.c 
b/xen/arch/x86/x86_64/asm-offsets.c
index 5d7a8e5..beac5ca 100644
--- a/xen/arch/x86/x86_64/asm-offsets.c
+++ b/xen/arch/x86/x86_64/asm-offsets.c
@@ -174,6 +174,7 @@ 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);
diff --git a/xen/include/xen/multiboot2.h b/xen/include/xen/multiboot2.h
index 8dd5800..feb4297 100644
--- a/xen/include/xen/multiboot2.h
+++ b/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
@@ -120,6 +127,12 @@ typedef struct {
 typedef struct {
     u32 type;
     u32 size;
+    u32 load_base_addr;
+} multiboot2_tag_load_base_addr_t;
+
+typedef struct {
+    u32 type;
+    u32 size;
     char string[];
 } multiboot2_tag_string_t;
 
-- 
1.7.10.4


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