multiboot2: Add support for relocatable images

Currently multiboot2 protocol loads image exactly at address specified in
ELF or multiboot2 header. This solution works quite well on legacy BIOS
platforms. It is possible because memory regions are placed at predictable
addresses (though I was not able to find any spec which says that it is
strong requirement, so, it looks that it is just a goodwill of hardware
designers). However, EFI platforms are more volatile. Even if required
memory regions live at specific addresses then they are sometimes simply
not free (e.g. used by boot/runtime services on Dell PowerEdge R820 and
OVMF). This means that you are not able to just set up final image
destination on build time. You have to provide method to relocate image
contents to real load address which is usually different than load address
specified in ELF and multiboot2 headers.

This patch provides all needed machinery to do self relocation in image code.
First of all GRUB2 reads min_addr (min. load addr), max_addr (max. load addr),
align (required image alignment), preference (it says which memory regions are
preferred by image, e.g. none, low, high) from multiboot_header_tag_relocatable
header tag contained in binary (at this stage load addresses from multiboot2
and/or ELF headers are ignored). Later loader tries to fulfill request (not only
that one) and if it succeeds then it informs image about real load address via
multiboot_tag_load_base_addr tag. At this stage GRUB2 role is finished. Starting
from now executable must cope with relocations itself using whole static and
dynamic knowledge provided by boot loader.

This patch does not provide functionality which could do relocations using
ELF relocation data. However, I was asked by Konrad Rzeszutek Wilk and Vladimir
'phcoder' Serbinenko to investigate that thing. It looks that relevant machinery
could be added to existing code (including this patch) without huge effort.
Additionally, ELF relocation could live in parallel with self relocation provided
by this patch. However, during research I realized that first of all we should
establish the details how ELF relocatable image should look like and how it should
be build. At least to build proper test/example files.

So, this patch just provides support for self relocatable images. If ELF file
with relocs is loaded then GRUB2 complains loudly and ignores it. Support for
such files will be added later.

This patch was tested with Xen image which uses that functionality. However, this Xen
feature is still under development and new patchset will be released in about 2-3 weeks.

Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Vladimir Serbinenko <phcoder@gmail.com>

grub-core/loader/i386/multiboot_mbi.c

@@ -70,9 +70,18 @@ load_kernel (grub_file_t file, const char *filename,
 	     char *buffer, struct multiboot_header *header)
 {
   grub_err_t err;
+  mbi_load_data_t mld;
+
+  mld.file = file;
+  mld.filename = filename;
+  mld.buffer = buffer;
+  mld.mbi_ver = 1;
+  mld.relocatable = 0;
+  mld.avoid_efi_boot_services = 0;
+
   if (grub_multiboot_quirks & GRUB_MULTIBOOT_QUIRK_BAD_KLUDGE)
     {
-      err = grub_multiboot_load_elf (file, filename, buffer);
+      err = grub_multiboot_load_elf (&mld);
       if (err == GRUB_ERR_NONE) {
 	return GRUB_ERR_NONE;
       }
@@ -121,7 +130,7 @@ load_kernel (grub_file_t file, const char *filename,
       return GRUB_ERR_NONE;
     }
 
-  return grub_multiboot_load_elf (file, filename, buffer);
+  return grub_multiboot_load_elf (&mld);
 }
 
 static struct multiboot_header *

grub-core/loader/multiboot.c

@@ -207,13 +207,12 @@ static grub_uint64_t highest_load;
 
 /* Load ELF32 or ELF64.  */
 grub_err_t
-grub_multiboot_load_elf (grub_file_t file, const char *filename,
+grub_multiboot_load_elf (mbi_load_data_t *mld)
-			 void *buffer)
 {
-  if (grub_multiboot_is_elf32 (buffer))
+  if (grub_multiboot_is_elf32 (mld->buffer))
-    return grub_multiboot_load_elf32 (file, filename, buffer);
+    return grub_multiboot_load_elf32 (mld);
-  else if (grub_multiboot_is_elf64 (buffer))
+  else if (grub_multiboot_is_elf64 (mld->buffer))
-    return grub_multiboot_load_elf64 (file, filename, buffer);
+    return grub_multiboot_load_elf64 (mld);
 
   return grub_error (GRUB_ERR_UNKNOWN_OS, N_("invalid arch-dependent ELF magic"));
 }

grub-core/loader/multiboot_elfxx.c

@@ -51,11 +51,15 @@ CONCAT(grub_multiboot_is_elf, XX) (void *buffer)
 }
 
 static grub_err_t
-CONCAT(grub_multiboot_load_elf, XX) (grub_file_t file, const char *filename, void *buffer)
+CONCAT(grub_multiboot_load_elf, XX) (mbi_load_data_t *mld)
 {
-  Elf_Ehdr *ehdr = (Elf_Ehdr *) buffer;
+  Elf_Ehdr *ehdr = (Elf_Ehdr *) mld->buffer;
   char *phdr_base;
+  grub_err_t err;
+  grub_relocator_chunk_t ch;
+  grub_uint32_t load_offset, load_size;
   int i;
+  void *source;
 
   if (ehdr->e_ident[EI_MAG0] != ELFMAG0
       || ehdr->e_ident[EI_MAG1] != ELFMAG1
@@ -75,54 +79,86 @@ CONCAT(grub_multiboot_load_elf, XX) (grub_file_t file, const char *filename, voi
   if (ehdr->e_phoff + (grub_uint32_t) ehdr->e_phnum * ehdr->e_phentsize > MULTIBOOT_SEARCH)
     return grub_error (GRUB_ERR_BAD_OS, "program header at a too high offset");
 
-  phdr_base = (char *) buffer + ehdr->e_phoff;
+  phdr_base = (char *) mld->buffer + ehdr->e_phoff;
 #define phdr(i)			((Elf_Phdr *) (phdr_base + (i) * ehdr->e_phentsize))
 
+  mld->link_base_addr = ~0;
+
+  /* Calculate lowest and highest load address.  */
+  for (i = 0; i < ehdr->e_phnum; i++)
+    if (phdr(i)->p_type == PT_LOAD)
+      {
+	mld->link_base_addr = grub_min (mld->link_base_addr, phdr(i)->p_paddr);
+	highest_load = grub_max (highest_load, phdr(i)->p_paddr + phdr(i)->p_memsz);
+      }
+
+#ifdef MULTIBOOT_LOAD_ELF64
+  if (highest_load >= 0x100000000)
+    return grub_error (GRUB_ERR_BAD_OS, "segment crosses 4 GiB border");
+#endif
+
+  load_size = highest_load - mld->link_base_addr;
+
+  if (mld->relocatable)
+    {
+      if (load_size > mld->max_addr || mld->min_addr > mld->max_addr - load_size)
+	return grub_error (GRUB_ERR_BAD_OS, "invalid min/max address and/or load size");
+
+      err = grub_relocator_alloc_chunk_align (grub_multiboot_relocator, &ch,
+					      mld->min_addr, mld->max_addr - load_size,
+					      load_size, mld->align ? mld->align : 1,
+					      mld->preference, mld->avoid_efi_boot_services);
+    }
+  else
+    err = grub_relocator_alloc_chunk_addr (grub_multiboot_relocator, &ch,
+					   mld->link_base_addr, load_size);
+
+  if (err)
+    {
+      grub_dprintf ("multiboot_loader", "Cannot allocate memory for OS image\n");
+      return err;
+    }
+
+  mld->load_base_addr = get_physical_target_address (ch);
+  source = get_virtual_current_address (ch);
+
+  grub_dprintf ("multiboot_loader", "link_base_addr=0x%x, load_base_addr=0x%x, "
+		"load_size=0x%x, relocatable=%d\n", mld->link_base_addr,
+		mld->load_base_addr, load_size, mld->relocatable);
+
+  if (mld->relocatable)
+    grub_dprintf ("multiboot_loader", "align=0x%lx, preference=0x%x, avoid_efi_boot_services=%d\n",
+		  (long) mld->align, mld->preference, mld->avoid_efi_boot_services);
+
   /* Load every loadable segment in memory.  */
   for (i = 0; i < ehdr->e_phnum; i++)
     {
       if (phdr(i)->p_type == PT_LOAD)
         {
-	  grub_err_t err;
-	  void *source;
-
-	  if (phdr(i)->p_paddr + phdr(i)->p_memsz > highest_load)
-	    highest_load = phdr(i)->p_paddr + phdr(i)->p_memsz;
 
 	  grub_dprintf ("multiboot_loader", "segment %d: paddr=0x%lx, memsz=0x%lx, vaddr=0x%lx\n",
 			i, (long) phdr(i)->p_paddr, (long) phdr(i)->p_memsz, (long) phdr(i)->p_vaddr);
 
-	  {
+	  load_offset = phdr(i)->p_paddr - mld->link_base_addr;
-	    grub_relocator_chunk_t ch;
-	    err = grub_relocator_alloc_chunk_addr (grub_multiboot_relocator, 
-						   &ch, phdr(i)->p_paddr,
-						   phdr(i)->p_memsz);
-	    if (err)
-	      {
-		grub_dprintf ("multiboot_loader", "Error loading phdr %d\n", i);
-		return err;
-	      }
-	    source = get_virtual_current_address (ch);
-	  }
 
 	  if (phdr(i)->p_filesz != 0)
 	    {
-	      if (grub_file_seek (file, (grub_off_t) phdr(i)->p_offset)
+	      if (grub_file_seek (mld->file, (grub_off_t) phdr(i)->p_offset)
 		  == (grub_off_t) -1)
 		return grub_errno;
 
-	      if (grub_file_read (file, source, phdr(i)->p_filesz)
+	      if (grub_file_read (mld->file, (grub_uint8_t *) source + load_offset, phdr(i)->p_filesz)
 		  != (grub_ssize_t) phdr(i)->p_filesz)
 		{
 		  if (!grub_errno)
 		    grub_error (GRUB_ERR_FILE_READ_ERROR, N_("premature end of file %s"),
-				filename);
+				mld->filename);
 		  return grub_errno;
 		}
 	    }
 
           if (phdr(i)->p_filesz < phdr(i)->p_memsz)
-            grub_memset ((grub_uint8_t *) source + phdr(i)->p_filesz, 0,
+            grub_memset ((grub_uint8_t *) source + load_offset + phdr(i)->p_filesz, 0,
 			 phdr(i)->p_memsz - phdr(i)->p_filesz);
         }
     }
@@ -168,18 +204,18 @@ CONCAT(grub_multiboot_load_elf, XX) (grub_file_t file, const char *filename, voi
       if (!shdr)
 	return grub_errno;
       
-      if (grub_file_seek (file, ehdr->e_shoff) == (grub_off_t) -1)
+      if (grub_file_seek (mld->file, ehdr->e_shoff) == (grub_off_t) -1)
 	{
 	  grub_free (shdr);
 	  return grub_errno;
 	}
 
-      if (grub_file_read (file, shdr, (grub_uint32_t) ehdr->e_shnum * ehdr->e_shentsize)
+      if (grub_file_read (mld->file, shdr, (grub_uint32_t) ehdr->e_shnum * ehdr->e_shentsize)
               != (grub_ssize_t) ehdr->e_shnum * ehdr->e_shentsize)
 	{
 	  if (!grub_errno)
 	    grub_error (GRUB_ERR_FILE_READ_ERROR, N_("premature end of file %s"),
-			filename);
+			mld->filename);
 	  return grub_errno;
 	}
       
@@ -189,7 +225,9 @@ CONCAT(grub_multiboot_load_elf, XX) (grub_file_t file, const char *filename, voi
 	  Elf_Shdr *sh = (Elf_Shdr *) shdrptr;
 	  void *src;
 	  grub_addr_t target;
-	  grub_err_t err;
+
+	  if (mld->mbi_ver >= 2 && (sh->sh_type == SHT_REL || sh->sh_type == SHT_RELA))
+	    return grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET, "ELF files with relocs are not supported yet");
 
 	  /* This section is a loaded section,
 	     so we don't care.  */
@@ -200,33 +238,28 @@ CONCAT(grub_multiboot_load_elf, XX) (grub_file_t file, const char *filename, voi
 	  if (sh->sh_size == 0)
 	    continue;
 
-	  {
+	  err = grub_relocator_alloc_chunk_align (grub_multiboot_relocator, &ch, 0,
-	    grub_relocator_chunk_t ch;
+						  (0xffffffff - sh->sh_size) + 1,
-	    err = grub_relocator_alloc_chunk_align (grub_multiboot_relocator,
+						  sh->sh_size, sh->sh_addralign,
-						    &ch, 0,
+						  GRUB_RELOCATOR_PREFERENCE_NONE,
-						    (0xffffffff - sh->sh_size)
+						  mld->avoid_efi_boot_services);
-						    + 1, sh->sh_size,
+	  if (err)
-						    sh->sh_addralign,
+	    {
-						    GRUB_RELOCATOR_PREFERENCE_NONE,
+	      grub_dprintf ("multiboot_loader", "Error loading shdr %d\n", i);
-						    0);
+	      return err;
-	    if (err)
+	    }
-	      {
+	  src = get_virtual_current_address (ch);
-		grub_dprintf ("multiboot_loader", "Error loading shdr %d\n", i);
+	  target = get_physical_target_address (ch);
-		return err;
-	      }
-	    src = get_virtual_current_address (ch);
-	    target = get_physical_target_address (ch);
-	  }
 
-	  if (grub_file_seek (file, sh->sh_offset) == (grub_off_t) -1)
+	  if (grub_file_seek (mld->file, sh->sh_offset) == (grub_off_t) -1)
 	    return grub_errno;
 
-          if (grub_file_read (file, src, sh->sh_size)
+          if (grub_file_read (mld->file, src, sh->sh_size)
               != (grub_ssize_t) sh->sh_size)
 	    {
 	      if (!grub_errno)
 		grub_error (GRUB_ERR_FILE_READ_ERROR, N_("premature end of file %s"),
-			    filename);
+			    mld->filename);
 	      return grub_errno;
 	    }
 	  sh->sh_addr = target;

grub-core/loader/multiboot_mbi2.c

@@ -68,6 +68,7 @@ static grub_size_t elf_sec_num, elf_sec_entsize;
 static unsigned elf_sec_shstrndx;
 static void *elf_sections;
 static int keep_bs = 0;
+static grub_uint32_t load_base_addr;
 
 void
 grub_multiboot_add_elfsyms (grub_size_t num, grub_size_t entsize,
@@ -101,36 +102,40 @@ find_header (grub_properly_aligned_t *buffer, grub_ssize_t len)
 grub_err_t
 grub_multiboot_load (grub_file_t file, const char *filename)
 {
-  grub_properly_aligned_t *buffer;
   grub_ssize_t len;
   struct multiboot_header *header;
   grub_err_t err;
   struct multiboot_header_tag *tag;
   struct multiboot_header_tag_address *addr_tag = NULL;
+  struct multiboot_header_tag_relocatable *rel_tag;
   int entry_specified = 0, efi_entry_specified = 0;
   grub_addr_t entry = 0, efi_entry = 0;
   grub_uint32_t console_required = 0;
   struct multiboot_header_tag_framebuffer *fbtag = NULL;
   int accepted_consoles = GRUB_MULTIBOOT_CONSOLE_EGA_TEXT;
+  mbi_load_data_t mld;
 
-  buffer = grub_malloc (MULTIBOOT_SEARCH);
+  mld.mbi_ver = 2;
-  if (!buffer)
+  mld.relocatable = 0;
+
+  mld.buffer = grub_malloc (MULTIBOOT_SEARCH);
+  if (!mld.buffer)
     return grub_errno;
 
-  len = grub_file_read (file, buffer, MULTIBOOT_SEARCH);
+  len = grub_file_read (file, mld.buffer, MULTIBOOT_SEARCH);
   if (len < 32)
     {
-      grub_free (buffer);
+      grub_free (mld.buffer);
       return grub_error (GRUB_ERR_BAD_OS, N_("premature end of file %s"), filename);
     }
 
   COMPILE_TIME_ASSERT (MULTIBOOT_HEADER_ALIGN % 4 == 0);
 
-  header = find_header (buffer, len);
+  header = find_header (mld.buffer, len);
 
   if (header == 0)
     {
-      grub_free (buffer);
+      grub_free (mld.buffer);
       return grub_error (GRUB_ERR_BAD_ARGUMENT, "no multiboot header found");
     }
 
@@ -174,10 +179,11 @@ grub_multiboot_load (grub_file_t file, const char *filename)
 	      case MULTIBOOT_TAG_TYPE_EFI_BS:
 	      case MULTIBOOT_TAG_TYPE_EFI32_IH:
 	      case MULTIBOOT_TAG_TYPE_EFI64_IH:
+	      case MULTIBOOT_TAG_TYPE_LOAD_BASE_ADDR:
 		break;
 
 	      default:
-		grub_free (buffer);
+		grub_free (mld.buffer);
 		return grub_error (GRUB_ERR_UNKNOWN_OS,
 				   "unsupported information tag: 0x%x",
 				   request_tag->requests[i]);
@@ -215,6 +221,27 @@ grub_multiboot_load (grub_file_t file, const char *filename)
 	accepted_consoles |= GRUB_MULTIBOOT_CONSOLE_FRAMEBUFFER;
 	break;
 
+      case MULTIBOOT_HEADER_TAG_RELOCATABLE:
+	mld.relocatable = 1;
+	rel_tag = (struct multiboot_header_tag_relocatable *) tag;
+	mld.min_addr = rel_tag->min_addr;
+	mld.max_addr = rel_tag->max_addr;
+	mld.align = rel_tag->align;
+	switch (rel_tag->preference)
+	  {
+	  case MULTIBOOT_LOAD_PREFERENCE_LOW:
+	    mld.preference = GRUB_RELOCATOR_PREFERENCE_LOW;
+	    break;
+
+	  case MULTIBOOT_LOAD_PREFERENCE_HIGH:
+	    mld.preference = GRUB_RELOCATOR_PREFERENCE_HIGH;
+	    break;
+
+	  default:
+	    mld.preference = GRUB_RELOCATOR_PREFERENCE_NONE;
+	  }
+	break;
+
 	/* GRUB always page-aligns modules.  */
       case MULTIBOOT_HEADER_TAG_MODULE_ALIGN:
 	break;
@@ -228,7 +255,7 @@ grub_multiboot_load (grub_file_t file, const char *filename)
       default:
 	if (! (tag->flags & MULTIBOOT_HEADER_TAG_OPTIONAL))
 	  {
-	    grub_free (buffer);
+	    grub_free (mld.buffer);
 	    return grub_error (GRUB_ERR_UNKNOWN_OS,
 			       "unsupported tag: 0x%x", tag->type);
 	  }
@@ -237,7 +264,7 @@ grub_multiboot_load (grub_file_t file, const char *filename)
 
   if (addr_tag && !entry_specified && !(keep_bs && efi_entry_specified))
     {
-      grub_free (buffer);
+      grub_free (mld.buffer);
       return grub_error (GRUB_ERR_UNKNOWN_OS,
 			 "load address tag without entry address tag");
     }
@@ -246,8 +273,8 @@ grub_multiboot_load (grub_file_t file, const char *filename)
     {
       grub_uint64_t load_addr = (addr_tag->load_addr + 1)
 	? addr_tag->load_addr : (addr_tag->header_addr
-				 - ((char *) header - (char *) buffer));
+				 - ((char *) header - (char *) mld.buffer));
-      int offset = ((char *) header - (char *) buffer -
+      int offset = ((char *) header - (char *) mld.buffer -
 	   (addr_tag->header_addr - load_addr));
       int load_size = ((addr_tag->load_end_addr == 0) ? file->size - offset :
 		       addr_tag->load_end_addr - addr_tag->load_addr);
@@ -260,27 +287,50 @@ grub_multiboot_load (grub_file_t file, const char *filename)
       else
 	code_size = load_size;
 
-      err = grub_relocator_alloc_chunk_addr (grub_multiboot_relocator, 
+      if (mld.relocatable)
-					     &ch, load_addr,
+	{
-					     code_size);
+	  if (code_size > mld.max_addr || mld.min_addr > mld.max_addr - code_size)
+	    {
+	      grub_free (mld.buffer);
+	      return grub_error (GRUB_ERR_BAD_OS, "invalid min/max address and/or load size");
+	    }
+
+	  err = grub_relocator_alloc_chunk_align (grub_multiboot_relocator, &ch,
+						  mld.min_addr, mld.max_addr - code_size,
+						  code_size, mld.align ? mld.align : 1,
+						  mld.preference, keep_bs);
+	}
+      else
+	err = grub_relocator_alloc_chunk_addr (grub_multiboot_relocator,
+					       &ch, load_addr, code_size);
       if (err)
 	{
 	  grub_dprintf ("multiboot_loader", "Error loading aout kludge\n");
-	  grub_free (buffer);
+	  grub_free (mld.buffer);
 	  return err;
 	}
+      mld.link_base_addr = load_addr;
+      mld.load_base_addr = get_physical_target_address (ch);
       source = get_virtual_current_address (ch);
 
+      grub_dprintf ("multiboot_loader", "link_base_addr=0x%x, load_base_addr=0x%x, "
+		    "load_size=0x%lx, relocatable=%d\n", mld.link_base_addr,
+		    mld.load_base_addr, (long) code_size, mld.relocatable);
+
+      if (mld.relocatable)
+	grub_dprintf ("multiboot_loader", "align=0x%lx, preference=0x%x, avoid_efi_boot_services=%d\n",
+		      (long) mld.align, mld.preference, keep_bs);
+
       if ((grub_file_seek (file, offset)) == (grub_off_t) -1)
 	{
-	  grub_free (buffer);
+	  grub_free (mld.buffer);
 	  return grub_errno;
 	}
 
       grub_file_read (file, source, load_size);
       if (grub_errno)
 	{
-	  grub_free (buffer);
+	  grub_free (mld.buffer);
 	  return grub_errno;
 	}
 
@@ -290,19 +340,41 @@ grub_multiboot_load (grub_file_t file, const char *filename)
     }
   else
     {
-      err = grub_multiboot_load_elf (file, filename, buffer);
+      mld.file = file;
+      mld.filename = filename;
+      mld.avoid_efi_boot_services = keep_bs;
+      err = grub_multiboot_load_elf (&mld);
       if (err)
 	{
-	  grub_free (buffer);
+	  grub_free (mld.buffer);
 	  return err;
 	}
     }
 
+  load_base_addr = mld.load_base_addr;
+
   if (keep_bs && efi_entry_specified)
     grub_multiboot_payload_eip = efi_entry;
   else if (entry_specified)
     grub_multiboot_payload_eip = entry;
 
+  if (mld.relocatable)
+    {
+      /*
+       * Both branches are mathematically equivalent. However, it looks
+       * that real life (C?) is more complicated. I am trying to avoid
+       * wrap around here if mld.load_base_addr < mld.link_base_addr.
+       * If you look at C operator precedence then everything should work.
+       * However, I am not 100% sure that a given compiler will not
+       * optimize/break this stuff. So, maybe we should use signed
+       * 64-bit int here.
+       */
+      if (mld.load_base_addr >= mld.link_base_addr)
+	grub_multiboot_payload_eip += mld.load_base_addr - mld.link_base_addr;
+      else
+	grub_multiboot_payload_eip -= mld.link_base_addr - mld.load_base_addr;
+    }
+
   if (fbtag)
     err = grub_multiboot_set_console (GRUB_MULTIBOOT_CONSOLE_FRAMEBUFFER,
 				      accepted_consoles,
@@ -411,6 +483,7 @@ grub_multiboot_get_mbi_size (void)
     + ALIGN_UP (sizeof (struct multiboot_tag_framebuffer), MULTIBOOT_TAG_ALIGN)
     + ALIGN_UP (sizeof (struct multiboot_tag_old_acpi)
 		+ sizeof (struct grub_acpi_rsdp_v10), MULTIBOOT_TAG_ALIGN)
+    + ALIGN_UP (sizeof (struct multiboot_tag_load_base_addr), MULTIBOOT_TAG_ALIGN)
     + acpiv2_size ()
     + net_size ()
 #ifdef GRUB_MACHINE_EFI
@@ -693,6 +766,15 @@ grub_multiboot_make_mbi (grub_uint32_t *target)
 		       % sizeof (grub_properly_aligned_t) == 0);
   ptrorig += (2 * sizeof (grub_uint32_t)) / sizeof (grub_properly_aligned_t);
 
+  {
+    struct multiboot_tag_load_base_addr *tag = (struct multiboot_tag_load_base_addr *) ptrorig;
+    tag->type = MULTIBOOT_TAG_TYPE_LOAD_BASE_ADDR;
+    tag->size = sizeof (struct multiboot_tag_load_base_addr);
+    tag->load_base_addr = load_base_addr;
+    ptrorig += ALIGN_UP (tag->size, MULTIBOOT_TAG_ALIGN)
+       / sizeof (grub_properly_aligned_t);
+  }
+
   {
     struct multiboot_tag_string *tag = (struct multiboot_tag_string *) ptrorig;
     tag->type = MULTIBOOT_TAG_TYPE_CMDLINE;

include/grub/multiboot.h

@@ -91,10 +91,28 @@ grub_multiboot_set_console (int console_type, int accepted_consoles,
 			    int console_required);
 grub_err_t
 grub_multiboot_load (grub_file_t file, const char *filename);
+
+struct mbi_load_data
+{
+  grub_file_t file;
+  const char *filename;
+  void *buffer;
+  unsigned int mbi_ver;
+  int relocatable;
+  grub_uint32_t min_addr;
+  grub_uint32_t max_addr;
+  grub_size_t align;
+  grub_uint32_t preference;
+  grub_uint32_t link_base_addr;
+  grub_uint32_t load_base_addr;
+  int avoid_efi_boot_services;
+};
+typedef struct mbi_load_data mbi_load_data_t;
+
 /* Load ELF32 or ELF64.  */
 grub_err_t
-grub_multiboot_load_elf (grub_file_t file, const char *filename,
+grub_multiboot_load_elf (mbi_load_data_t *mld);
-			 void *buffer);
+
 extern grub_size_t grub_multiboot_pure_size;
 extern grub_size_t grub_multiboot_alloc_mbi;
 extern grub_uint32_t grub_multiboot_payload_eip;

include/multiboot2.h

@@ -62,6 +62,7 @@
 #define MULTIBOOT_TAG_TYPE_EFI_BS            18
 #define MULTIBOOT_TAG_TYPE_EFI32_IH          19
 #define MULTIBOOT_TAG_TYPE_EFI64_IH          20
+#define MULTIBOOT_TAG_TYPE_LOAD_BASE_ADDR    21
 
 #define MULTIBOOT_HEADER_TAG_END  0
 #define MULTIBOOT_HEADER_TAG_INFORMATION_REQUEST  1
@@ -72,11 +73,16 @@
 #define MULTIBOOT_HEADER_TAG_MODULE_ALIGN  6
 #define MULTIBOOT_HEADER_TAG_EFI_BS  7
 #define MULTIBOOT_HEADER_TAG_ENTRY_ADDRESS_EFI64  9
+#define MULTIBOOT_HEADER_TAG_RELOCATABLE  10
 
 #define MULTIBOOT_ARCHITECTURE_I386  0
 #define MULTIBOOT_ARCHITECTURE_MIPS32  4
 #define MULTIBOOT_HEADER_TAG_OPTIONAL 1
 
+#define MULTIBOOT_LOAD_PREFERENCE_NONE 0
+#define MULTIBOOT_LOAD_PREFERENCE_LOW 1
+#define MULTIBOOT_LOAD_PREFERENCE_HIGH 2
+
 #define MULTIBOOT_CONSOLE_FLAGS_CONSOLE_REQUIRED 1
 #define MULTIBOOT_CONSOLE_FLAGS_EGA_TEXT_SUPPORTED 2
 
@@ -161,6 +167,17 @@ struct multiboot_header_tag_module_align
   multiboot_uint32_t size;
 };
 
+struct multiboot_header_tag_relocatable
+{
+  multiboot_uint16_t type;
+  multiboot_uint16_t flags;
+  multiboot_uint32_t size;
+  multiboot_uint32_t min_addr;
+  multiboot_uint32_t max_addr;
+  multiboot_uint32_t align;
+  multiboot_uint32_t preference;
+};
+
 struct multiboot_color
 {
   multiboot_uint8_t red;
@@ -387,6 +404,13 @@ struct multiboot_tag_efi64_ih
   multiboot_uint64_t pointer;
 };
 
+struct multiboot_tag_load_base_addr
+{
+  multiboot_uint32_t type;
+  multiboot_uint32_t size;
+  multiboot_uint32_t load_base_addr;
+};
+
 #endif /* ! ASM_FILE */
 
 #endif /* ! MULTIBOOT_HEADER */