grub2/0132-chainloader-patch-in-BPB-s-sectors_per_track-and-num.patch

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From c225298038f0e7e7ec2d783776fba880d9965f16 Mon Sep 17 00:00:00 2001
From: "C. Masloch" <pushbx@38.de>
Date: Thu, 1 Feb 2018 15:51:55 +0100
Subject: [PATCH] chainloader: patch in BPB's sectors_per_track and num_heads
These fields must reflect the ROM-BIOS's geometry for CHS-based
loaders to correctly load their next stage. Most loaders do not
query the ROM-BIOS (Int13.08), relying on the BPB fields to hold
the correct values already.
Tested with lDebug booted in qemu via grub2's
FreeDOS direct loading support, refer to
https://bitbucket.org/ecm/ldosboot + https://bitbucket.org/ecm/ldebug
(For this test, lDebug's iniload.asm must be assembled with
-D_QUERY_GEOMETRY=0 to leave the BPB values provided by grub.)
Signed-off-by: C. Masloch <pushbx@38.de>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
grub-core/loader/i386/pc/chainloader.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
diff --git a/grub-core/loader/i386/pc/chainloader.c b/grub-core/loader/i386/pc/chainloader.c
index 18220b7aaab..ef3a322b78c 100644
--- a/grub-core/loader/i386/pc/chainloader.c
+++ b/grub-core/loader/i386/pc/chainloader.c
@@ -19,6 +19,7 @@
#include <grub/loader.h>
#include <grub/machine/chainloader.h>
+#include <grub/machine/biosdisk.h>
#include <grub/machine/memory.h>
#include <grub/file.h>
#include <grub/err.h>
@@ -86,9 +87,16 @@ grub_chainloader_unload (void)
void
grub_chainloader_patch_bpb (void *bs, grub_device_t dev, grub_uint8_t dl)
{
- grub_uint32_t part_start = 0;
+ grub_uint32_t part_start = 0, heads = 0, sectors = 0;
if (dev && dev->disk)
- part_start = grub_partition_get_start (dev->disk->partition);
+ {
+ part_start = grub_partition_get_start (dev->disk->partition);
+ if (dev->disk->data)
+ {
+ heads = ((struct grub_biosdisk_data *)(dev->disk->data))->heads;
+ sectors = ((struct grub_biosdisk_data *)(dev->disk->data))->sectors;
+ }
+ }
if (grub_memcmp ((char *) &((struct grub_ntfs_bpb *) bs)->oem_name,
"NTFS", 4) == 0)
{
@@ -127,12 +135,20 @@ grub_chainloader_patch_bpb (void *bs, grub_device_t dev, grub_uint8_t dl)
{
bpb->num_hidden_sectors = grub_cpu_to_le32 (part_start);
bpb->version_specific.fat12_or_fat16.num_ph_drive = dl;
+ if (sectors)
+ bpb->sectors_per_track = grub_cpu_to_le16 (sectors);
+ if (heads)
+ bpb->num_heads = grub_cpu_to_le16 (heads);
return;
}
if (bpb->version_specific.fat32.sectors_per_fat_32)
{
bpb->num_hidden_sectors = grub_cpu_to_le32 (part_start);
bpb->version_specific.fat32.num_ph_drive = dl;
+ if (sectors)
+ bpb->sectors_per_track = grub_cpu_to_le16 (sectors);
+ if (heads)
+ bpb->num_heads = grub_cpu_to_le16 (heads);
return;
}
break;