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| author | H. Peter Anvin <hpa@zytor.com> | 2007-04-10 15:23:30 -0700 |
|---|---|---|
| committer | H. Peter Anvin <hpa@zytor.com> | 2007-04-10 15:23:30 -0700 |
| commit | 2621cc62fd4c10b2b60c8335242b7e02b618448f (patch) | |
| tree | ce69946cb67a95f81762d441f803b8503f091122 /mbr/mbr.S | |
| parent | e93773c42fcf550bed275187d872c6e6ee7599bc (diff) | |
| download | syslinux.git-2621cc62fd4c10b2b60c8335242b7e02b618448f.tar.gz syslinux.git-2621cc62fd4c10b2b60c8335242b7e02b618448f.tar.xz syslinux.git-2621cc62fd4c10b2b60c8335242b7e02b618448f.zip | |
MBR: fix problems when LBA > 65535*sectors.
Fix division overflow bug when LBA > 65535*sectors. Bug report by
Devin Bayer.
Diffstat (limited to 'mbr/mbr.S')
| -rw-r--r-- | mbr/mbr.S | 35 |
1 files changed, 17 insertions, 18 deletions
@@ -29,10 +29,10 @@ .text .globl bootsec -stack = 0x7c00 -driveno = (stack-6) -heads = (stack-8) -sectors = (stack-10) +stack = 0x7c00 +driveno = (stack-6) +sectors = (stack-8) +secpercyl = (stack-10) BIOS_page = 0x462 @@ -89,12 +89,13 @@ next: /* Get (C)HS geometry */ movb $0x08, %ah int $0x13 + andw $0x3f, %cx /* Sector count */ + pushw %cx /* Save sectors on the stack */ xorw %ax, %ax movb %dh, %al /* dh = number of heads */ incw %ax /* From 0-based to count */ - pushw %ax /* Save heads on the stack */ - andw $0x3f, %cx /* Sector count */ - pushw %cx /* Save sectors on the stack */ + mulw %cx /* Heads*sectors -> sectors per cylinder */ + pushw %ax /* Save sectors/cylinder on the stack */ xorl %eax, %eax pushl %eax /* Base */ @@ -112,18 +113,16 @@ read_sector: read_sector_cbios: movl %eax, %edx shrl $16, %edx - divw (sectors) - incw %dx - movw %dx, %cx - xorw %dx, %dx - divw (heads) - /* dx = head, ax = cylinder */ + divw (secpercyl) + rorb %ah + rorb %ah + movb %ah, %cl movb %al, %ch - shrw $2, %ax - shrw %ax - andb $0xc0, %al - orb %al, %cl - movb %dl, %dh + movw %dx, %ax + divb (sectors) + movb %al, %dh + incb %ah + orb %ah, %cl movw $bootsec, %bx movw $0x0201, %ax jmp read_common |