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File grub-iso-fixes of Package grub (Revision 6bb7e5602ee76484b24d754551744e79)

Currently displaying revision 6bb7e5602ee76484b24d754551744e79 , Show latest

From: Jeff Mahoney <jeffm@suse.com>
Subject: [PATCH] grub: Fix iso sector/offset calculations

This patch fixes iso9660 sector calculations when byte_offset is nonzero
 and the device sector size != file system sector. This is due to it
 accounting for the byte_offset before left-shifting the sector number
 instead of afterwards.

For example, the old code would make the following translation for a device
 with 512 byte sectors:

file system				device
 sector 10, offset 512			sector 44, offset 0
 10 * 2048 + 512 = 20992		44 * 512 = 22528

The correct translation is sector 41, offset 0: 41 * 512 = 20992

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
---

stage2/fsys_iso9660.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/stage2/fsys_iso9660.c
+++ b/stage2/fsys_iso9660.c
@@ -81,12 +86,12 @@ iso9660_devread (int sector, int byte_of
   if (byte_len <= 0)
     return 1;
 
-  sector += (byte_offset >> sector_size_lg2);
-  byte_offset &= (buf_geom.sector_size - 1);
   asm volatile ("shl%L0 %1,%0"
 		: "=r"(sector)
 		: "Ic"((int8_t)(ISO_SECTOR_BITS - sector_size_lg2)),
 		"0"(sector));
+  sector += (byte_offset >> sector_size_lg2);
+  byte_offset &= (buf_geom.sector_size - 1);
 
 #if !defined(STAGE1_5)
   if (disk_read_hook && debug)

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File grub-iso-fixes of Package grub (Revision 6bb7e5602ee76484b24d754551744e79)

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