Re: [Xen-devel] [PATCH v9 13/13] x86: add multiboot2 protocol support for relocatable images

[Jan Beulich]

>>> On 29.09.16 at 23:42,  wrote:
> 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 

Acked-by: Jan Beulich 


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[Xen-devel] [PATCH v9 13/13] x86: add multiboot2 protocol support for relocatable images

[Daniel Kiper]

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 
---
v9 - suggestions/fixes:
   - use .L labels instead of numeric ones in multiboot2 data scanning loop
 (suggested by Jan Beulich).

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  |   16 
 xen/arch/x86/x86_64/asm-offsets.c |1 +
 xen/include/xen/multiboot2.h  |   13 +
 3 files changed, 30 insertions(+)

diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index 26f48da..71c0273 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. */ \
+   0x, /* The end of image max load address (4 GiB - 
1). */ \
+   0x20, /* 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
@@ -384,6 +391,15 @@ __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
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_NONE0
+#define MULTIBOOT2_LOAD_PREFERENCE_LOW 1
+#define MULTIBOOT2_LOAD_PREFERENCE_HIGH2
+
 /* Header console tag console_flags. */
 #define MULTIBOOT2_CONSOLE_FLAGS_CONSOLE_REQUIRED  1
 #define MULTIBOOT2_CONSOLE_FLAGS_EGA_TEXT_SUPPORTED2
@@ -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