[PATCH] GRUB2 does not provide Multiboot Legacy memory map

[PATCH] GRUB2 does not provide Multiboot Legacy memory map

[Julian Salazar]

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Hi,

 

I'm developing a small kernel and I've been using GRUB2 with the Legacy
Multiboot Specification for some time now. I've noticed that it does not
provide some of the things in the Multiboot Information structure that GRUB
Legacy does, like the memory map. So I've created a small patch which works
in QEMU and real hardware so that GRUB2 will pass the memory map to my
kernel or any multiboot-compliant kernel for the i386-pc.

 

Since I've never actually contributed code to a GNU project before, are
there certain rules and regulations of some sort that I have to comply with
before I can send my patch here?

 

Thanks.


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Re: [PATCH] GRUB2 does not provide Multiboot Legacy memory map

[Thomas Schwinge]

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Hello!

On Sat, Apr 19, 2008 at 03:11:43PM -0600, Julian Salazar wrote:
> I'm developing a small kernel and I've been using GRUB2 with the Legacy
> Multiboot Specification for some time now. I've noticed that it does not
> provide some of the things in the Multiboot Information structure that GRUB
> Legacy does, like the memory map. So I've created a small patch which works
> in QEMU and real hardware so that GRUB2 will pass the memory map to my
> kernel or any multiboot-compliant kernel for the i386-pc.

Now this is interesting as I've just today seen an incompatibility
between booting a multiboot kernel with GRUB legacy and GRUB2.  It might
actually be the same issue, but I didn't fully investigate yet.
Therefore I'm quite interested in seeing your patch.


> Since I've never actually contributed code to a GNU project before, are

Welcome!

> there certain rules and regulations of some sort that I have to comply with

Your guessed right: sure there are :-).  See, for example, (parts of) the
GNU Coding Standards, <http://www.gnu.org/prep/standards/html_node/>.
Not everything is relevant in your case, though.

> before I can send my patch here?

Feel free to simply send it here and we'll tell you what needs to be
changed.


Regards,
 Thomas

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RE: [PATCH] GRUB2 does not provide Multiboot Legacy memory map

[Julian Salazar]

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Attached is the patch. Since I'm not completely familiar with GRUB2's
internals, there might be a more efficient way of implementing this.

Thoughts/improvements?

> -----Original Message-----
> From: grub-devel-bounces+julian.salazar=shaw.ca@gnu.org [mailto:grub-
> devel-bounces+julian.salazar=shaw.ca@gnu.org] On Behalf Of Thomas Schwinge
> Sent: April-19-08 3:32 PM
> To: Julian Salazar
> Cc: grub-devel@gnu.org
> Subject: Re: [PATCH] GRUB2 does not provide Multiboot Legacy memory map
> 
> Hello!
> 
> On Sat, Apr 19, 2008 at 03:11:43PM -0600, Julian Salazar wrote:
> > I'm developing a small kernel and I've been using GRUB2 with the Legacy
> > Multiboot Specification for some time now. I've noticed that it does not
> > provide some of the things in the Multiboot Information structure that
> GRUB
> > Legacy does, like the memory map. So I've created a small patch which
> works
> > in QEMU and real hardware so that GRUB2 will pass the memory map to my
> > kernel or any multiboot-compliant kernel for the i386-pc.
> 
> Now this is interesting as I've just today seen an incompatibility
> between booting a multiboot kernel with GRUB legacy and GRUB2.  It might
> actually be the same issue, but I didn't fully investigate yet.
> Therefore I'm quite interested in seeing your patch.
> 
> 
> > Since I've never actually contributed code to a GNU project before, are
> 
> Welcome!
> 
> > there certain rules and regulations of some sort that I have to comply
> with
> 
> Your guessed right: sure there are :-).  See, for example, (parts of) the
> GNU Coding Standards, <http://www.gnu.org/prep/standards/html_node/>.
> Not everything is relevant in your case, though.
> 
> > before I can send my patch here?
> 
> Feel free to simply send it here and we'll tell you what needs to be
> changed.
> 
> 
> Regards,
>  Thomas

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Index: loader/i386/pc/multiboot.c
===================================================================
RCS file: /sources/grub/grub2/loader/i386/pc/multiboot.c,v
retrieving revision 1.19
diff -u -p -r1.19 multiboot.c
--- loader/i386/pc/multiboot.c	5 Mar 2008 05:09:35 -0000	1.19
+++ loader/i386/pc/multiboot.c	19 Apr 2008 20:36:54 -0000
@@ -24,7 +24,6 @@
  *  - a.out support
  *  - boot device
  *  - symbol table
- *  - memory map
  *  - drives table
  *  - ROM configuration table
  *  - APM table
@@ -74,6 +73,7 @@ grub_multiboot_unload (void)
 	}
       grub_free ((void *) mbi->mods_addr);
       grub_free ((void *) mbi->cmdline);
+      grub_free ((void *) mbi->mmap_addr);
       grub_free (mbi);
     }
 
@@ -314,6 +314,10 @@ grub_multiboot (int argc, char *argv[])
   char buffer[MULTIBOOT_SEARCH], *cmdline = 0, *p;
   struct grub_multiboot_header *header;
   grub_ssize_t len;
+  struct grub_machine_mmap_entry *mmap_entry
+    = (struct grub_machine_mmap_entry *) GRUB_MEMORY_MACHINE_SCRATCH_ADDR;
+  struct grub_machine_mmap_entry *mmap;
+  grub_uint32_t cont;
   int i;
 
   grub_loader_unset ();
@@ -411,6 +415,26 @@ grub_multiboot (int argc, char *argv[])
   mbi->flags |= MULTIBOOT_INFO_CMDLINE;
   mbi->cmdline = (grub_uint32_t) cmdline;
 
+  /* Create memory map */
+  cont = grub_get_mmap_entry (mmap_entry, 0);
+
+  if (mmap_entry->size)
+    {
+      /* Allocate space for 32 memory map entries */
+      mmap = grub_malloc (sizeof (struct grub_machine_mmap_entry) * 32);
+      if (! mmap)
+        goto fail;
+      mmap[0] = *mmap_entry;
+      for (i = 1; cont; i++)
+        {
+          cont = grub_get_mmap_entry (mmap_entry, cont);
+          mmap[i] = *mmap_entry;
+        }
+      mbi->flags |= MULTIBOOT_INFO_MEM_MAP;
+      mbi->mmap_length = sizeof (struct grub_machine_mmap_entry) * i;
+      mbi->mmap_addr = (grub_uint32_t) mmap;
+    }
+
   mbi->flags |= MULTIBOOT_INFO_BOOT_LOADER_NAME;
   mbi->boot_loader_name = (grub_uint32_t) grub_strdup (PACKAGE_STRING);
 
@@ -426,6 +450,8 @@ grub_multiboot (int argc, char *argv[])
   if (grub_errno != GRUB_ERR_NONE)
     {
       grub_free (cmdline);
+      if (mbi->flags & MULTIBOOT_INFO_MEM_MAP)
+        grub_free (mmap);
       grub_free (mbi);
       grub_dl_unref (my_mod);
     }

Re: [PATCH] GRUB2 does not provide Multiboot Legacy memory map

[Robert Millan]

On Sat, Apr 19, 2008 at 04:09:15PM -0600, Julian Salazar wrote:
> Attached is the patch. Since I'm not completely familiar with GRUB2's
> internals, there might be a more efficient way of implementing this.
> 
> Thoughts/improvements?

Thanks for the patch.  It'd be interesting if it was done portably.  The
coreboot (aka LinuxBIOS) target also uses this code, and the memory map is
obtained differently there (see kern/i386/linuxbios/init.c).

At least, it could be #ifdef'ed, although it'd be nice to have something
more ellegant (e.g. an isolated, generic function to probe for memory map
arch-dependantly that arch-independant code can use).

-- 
Robert Millan

<GPLv2> I know my rights; I want my phone call!
<DRM> What use is a phone call… if you are unable to speak?
(as seen on /.)