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

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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: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
H. Peter Anvin 2007-07-31 16:17:13 -04:00
parent 8b608d2f5a
commit ff659d13ed
1 changed files with 3 additions and 2 deletions
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arch/i386/boot/edd.c
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@ -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)