Re: multiboot2 vs. grub2 implementation

[walt <wa1ter@myrealbox.com>]

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On Tue, 2008-02-05 at 14:23 -0600, jakllsch@kollasch.net wrote:
> On Sun, Feb 03, 2008 at 09:11:23AM -0800, walt wrote:
> > jakllsch@kollasch.net wrote:
> >> Hi,
> >>
> >> In the course of actually trying to use the MultibootDraft, I've 
> >> discovered
> >> some places where the draft and the grub2 implementation differ...
> >
> > Hi Jonathan,
> >
> > Are you using grub2/cvs with or without Bean's latest multiboot patch?
> 
> I tend not to be aware of these things.  I'm using stock sources.
> 
> > It still hasn't been committed, and I was about to ask about it anyway.
> > Without that patch, multiboot doesn't work.
> 
> Hmm.

Agreed :o)  Bean's patch had some whitespace corruption anyway, so here
it is again, diffed against today's latest cvs grub2:
========================================================================

this is the patch, problems found:

1, the mbi structure is not initialized to all zeros, this means some
important member, like mods_count, will contain trash.
2, the entry point in the header is virtual address, we need to
translate it to physical address.

        * loader/i386/pc/multiboot.c (grub_multiboot_load_elf32): Get
physical
        address of entry.
        (grub_multiboot_load_elf64): Likewise.
        (grub_multiboot): Initialize mbi structure.



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Index: loader/i386/pc/multiboot.c
===================================================================
RCS file: /sources/grub/grub2/loader/i386/pc/multiboot.c,v
retrieving revision 1.15
diff -u -r1.15 multiboot.c
--- loader/i386/pc/multiboot.c	2 Jan 2008 11:55:23 -0000	1.15
+++ loader/i386/pc/multiboot.c	6 Feb 2008 01:16:26 -0000
@@ -96,6 +96,7 @@
 {
   Elf32_Ehdr *ehdr = (Elf32_Ehdr *) buffer;
   Elf32_Phdr *phdr;
+  grub_addr_t real_entry = 0;
   int i;
 
   if (ehdr->e_ident[EI_CLASS] != ELFCLASS32)
@@ -144,9 +145,16 @@
           if (phdr->p_filesz < phdr->p_memsz)
             grub_memset ((char *) phdr->p_paddr + phdr->p_filesz, 0,
 			 phdr->p_memsz - phdr->p_filesz);
+
+          if ((entry >= phdr->p_vaddr) &&
+	      (entry < phdr->p_vaddr + phdr->p_memsz))
+	    real_entry = entry + phdr->p_paddr - phdr->p_vaddr;
         }
     }
-  
+
+  if (real_entry)
+    entry = real_entry;
+
   return grub_errno;
 }
 
@@ -164,6 +172,7 @@
 {
   Elf64_Ehdr *ehdr = (Elf64_Ehdr *) buffer;
   Elf64_Phdr *phdr;
+  grub_addr_t real_entry = 0;
   int i;
 
   if (ehdr->e_ident[EI_CLASS] != ELFCLASS64)
@@ -226,9 +235,16 @@
 			  + phdr->p_filesz),
 			 0,
 			 phdr->p_memsz - phdr->p_filesz);
+
+	  if ((entry >= phdr->p_vaddr) &&
+	      (entry < phdr->p_vaddr + phdr->p_memsz))
+	    real_entry = entry + phdr->p_paddr - phdr->p_vaddr;
         }
     }
-  
+
+  if (real_entry)
+    entry = real_entry;
+
   return grub_errno;
 }
 
@@ -306,6 +322,8 @@
   if (! mbi)
     goto fail;
 
+  grub_memset (mbi, 0, sizeof (struct grub_multiboot_info));
+
   mbi->flags = MULTIBOOT_INFO_MEMORY;
 
   /* Convert from bytes to kilobytes.  */