From c225298038f0e7e7ec2d783776fba880d9965f16 Mon Sep 17 00:00:00 2001 From: "C. Masloch" 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 Reviewed-by: Daniel Kiper --- 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 #include +#include #include #include #include @@ -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;