reed solomon breaks larger pxe images

reed solomon breaks larger pxe images

[Seth Goldberg]

Hi,

   While trying to test pxe booting, I noticed that creating a pxe image larger 
than around 100k causes the system hard-hang after control is transferred to 
pxegrub.  I narrowed it down to an unknown problem in 
grub_reed_solomon_recover (called from startup.S).  Unconditionally jumping 
over the call allows the system to continue to proceed to the menu.  So, if 
you're trying to build a pxe image with a lot of modules, and you get a hard 
hang, try this:

=== modified file 'grub-core/kern/i386/pc/startup.S'
--- grub-core/kern/i386/pc/startup.S    2010-12-24 06:29:28 +0000
+++ grub-core/kern/i386/pc/startup.S    2010-12-27 04:26:25 +0000
@@ -147,6 +147,8 @@
         incl    %eax
         call    grub_gate_a20

+       jmp post_reed_solomon
+
         movl    EXT_C(grub_compressed_size), %edx
         addl    $(GRUB_KERNEL_MACHINE_RAW_SIZE - 
GRUB_KERNEL_I386_PC_NO_REED_SOLOMON_PART), %edx
         movl    reed_solomon_redundancy, %ecx



  --S

Re: reed solomon breaks larger pxe images

[Vladimir 'φ-coder/phcoder' Serbinenko]

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On 12/27/2010 05:30 AM, Seth Goldberg wrote:
> Hi,
>
>   While trying to test pxe booting, I noticed that creating a pxe
> image larger than around 100k causes the system hard-hang after
> control is transferred to pxegrub.  I narrowed it down to an unknown
> problem in grub_reed_solomon_recover (called from startup.S). 
> Unconditionally jumping over the call allows the system to continue to
> proceed to the menu.  So, if you're trying to build a pxe image with a
> lot of modules, and you get a hard hang, try this:
>
Attached patch should fix the problem.
> === modified file 'grub-core/kern/i386/pc/startup.S'
> --- grub-core/kern/i386/pc/startup.S    2010-12-24 06:29:28 +0000
> +++ grub-core/kern/i386/pc/startup.S    2010-12-27 04:26:25 +0000
> @@ -147,6 +147,8 @@
>         incl    %eax
>         call    grub_gate_a20
>
> +       jmp post_reed_solomon
> +
>         movl    EXT_C(grub_compressed_size), %edx
>         addl    $(GRUB_KERNEL_MACHINE_RAW_SIZE -
> GRUB_KERNEL_I386_PC_NO_REED_SOLOMON_PART), %edx
>         movl    reed_solomon_redundancy, %ecx
>
>
>
>  --S
>
> _______________________________________________
> Grub-devel mailing list
> Grub-devel@gnu.org
> http://lists.gnu.org/mailman/listinfo/grub-devel
>


-- 
Regards
Vladimir 'φ-coder/phcoder' Serbinenko


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=== modified file 'grub-core/kern/i386/pc/startup.S'
--- grub-core/kern/i386/pc/startup.S	2010-12-04 16:19:26 +0000
+++ grub-core/kern/i386/pc/startup.S	2010-12-27 04:51:59 +0000
@@ -151,8 +151,6 @@
 	addl    $(GRUB_KERNEL_MACHINE_RAW_SIZE - GRUB_KERNEL_I386_PC_NO_REED_SOLOMON_PART), %edx
 	movl    reed_solomon_redundancy, %ecx
 	leal    _start + GRUB_KERNEL_I386_PC_NO_REED_SOLOMON_PART, %eax
-	testl   %edx, %edx
-	jz post_reed_solomon
 	call    EXT_C (grub_reed_solomon_recover)
 	jmp post_reed_solomon
 

=== modified file 'grub-core/lib/reed_solomon.c'
--- grub-core/lib/reed_solomon.c	2010-12-21 16:51:08 +0000
+++ grub-core/lib/reed_solomon.c	2010-12-27 05:06:01 +0000
@@ -372,6 +372,10 @@
       grub_size_t rr = (rs + SECTOR_SIZE - 1 - i) / SECTOR_SIZE;
       gf_single_t m[ds + rr];
 
+      /* Nothing to do.  */
+      if (!ds || !rr)
+	continue;
+
       for (j = 0; j < (int) ds; j++)
 	m[j] = ptr[SECTOR_SIZE * j + i];
       for (j = 0; j < (int) rr; j++)
@@ -414,6 +418,10 @@
   gf_single_t *ptr = buffer;
   gf_single_t *rptr = ptr + s;
 
+  /* Nothing to do.  */
+  if (!rs)
+    return;
+
   while (s > 0)
     {
       grub_size_t tt;
@@ -441,6 +449,10 @@
   gf_single_t *ptr = ptr_;
   gf_single_t *rptr = ptr + s;
 
+  /* Nothing to do.  */
+  if (!rs)
+    return;
+
 #if defined (STANDALONE)
   init_inverts ();
 #endif
@@ -454,8 +466,8 @@
       tt = cs + crs;
       if (tt > MAX_BLOCK_SIZE)
 	{
-	  cs = cs * MAX_BLOCK_SIZE / tt;
-	  crs = crs * MAX_BLOCK_SIZE / tt;
+	  cs = (cs * MAX_BLOCK_SIZE) / tt;
+	  crs = (crs * MAX_BLOCK_SIZE) / tt;
 	}
       decode_block (ptr, cs, rptr, crs);
       ptr += cs;


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