Commit ff659d13 authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

[x86 setup] EDD: Fix the computation of the MBR sector buffer 



Some BIOSes require that sector buffers not cross 64K
boundaries.  As a result, we compute a dynamic address on the
setup heap.  Unfortunately, this address computation was just
totally wrong.

Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
parent 8b608d2f

arch/i386/boot/edd.c

+3 −2
Original line number Diff line number Diff line
@@ -72,17 +72,18 @@ static u32 read_mbr_sig(u8 devno, struct edd_info *ei) 
	u32 mbrsig;

	u32 buf_base, mbr_base;

	extern char _end[];

	static char mbr_buf[1024];



	sector_size = ei->params.bytes_per_sector;

	if (!sector_size)

		sector_size = 512; /* Best available guess */



	/* Produce a naturally aligned buffer on the heap */

	buf_base = (ds() << 4) + (u32)&_end;

	mbr_base = (buf_base+sector_size-1) & ~(sector_size-1);

	mbrbuf_ptr = mbr_buf + (mbr_base-buf_base);

	mbrbuf_ptr = _end + (mbr_base-buf_base);

	mbrbuf_end = mbrbuf_ptr + sector_size;



	/* Make sure we actually have space on the heap... */

	if (!(boot_params.hdr.loadflags & CAN_USE_HEAP))

		return 0;

	if (mbrbuf_end > (char *)(size_t)boot_params.hdr.heap_end_ptr)