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chainloader: patch in BPB's sectors_per_track and num_heads

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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>
This commit is contained in:
C. Masloch 2018-02-01 15:51:55 +01:00 committed by Vincent Batts
parent b57c2a10af
commit b59db4f484
1 changed files with 18 additions and 2 deletions
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20
grub-core/loader/i386/pc/chainloader.c
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@ -19,6 +19,7 @@
#include <grub/loader.h> #include <grub/loader.h>
#include <grub/machine/chainloader.h> #include <grub/machine/chainloader.h>
#include <grub/machine/biosdisk.h>
#include <grub/machine/memory.h> #include <grub/machine/memory.h>
#include <grub/file.h> #include <grub/file.h>
#include <grub/err.h> #include <grub/err.h>
@ -86,9 +87,16 @@ grub_chainloader_unload (void)
void void
grub_chainloader_patch_bpb (void *bs, grub_device_t dev, grub_uint8_t dl) 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) 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, if (grub_memcmp ((char *) &((struct grub_ntfs_bpb *) bs)->oem_name,
"NTFS", 4) == 0) "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->num_hidden_sectors = grub_cpu_to_le32 (part_start);
bpb->version_specific.fat12_or_fat16.num_ph_drive = dl; 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; return;
} }
if (bpb->version_specific.fat32.sectors_per_fat_32) if (bpb->version_specific.fat32.sectors_per_fat_32)
{ {
bpb->num_hidden_sectors = grub_cpu_to_le32 (part_start); bpb->num_hidden_sectors = grub_cpu_to_le32 (part_start);
bpb->version_specific.fat32.num_ph_drive = dl; 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; return;
} }
break; break;