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| author | H. Peter Anvin <hpa@zytor.com> | 2007-07-11 16:22:46 -0700 |
|---|---|---|
| committer | H. Peter Anvin <hpa@zytor.com> | 2007-07-11 16:22:46 -0700 |
| commit | 9137770dd9710f802dd4ace76d85e8b976dc791b (patch) | |
| tree | 176c38089f107225f92539f93b0a5e581ddaaee3 /mbr | |
| parent | c89cafc9e4b08e62f6794425295a99f385d0a47b (diff) | |
| download | syslinux-9137770dd9710f802dd4ace76d85e8b976dc791b.tar.gz | |
Another 2 bytes off the MBR.
Diffstat (limited to 'mbr')
| -rw-r--r-- | mbr/mbr.S | 28 |
1 files changed, 13 insertions, 15 deletions
@@ -107,9 +107,10 @@ next: /* * read_sector: read a single sector pointed to by %eax to 0x7c00. - * CF is set on error. All registers clobbered. + * CF is set on error. All registers saved. */ read_sector: + pushal read_sector_cbios: xorl %edx, %edx divl (secpercyl) @@ -132,18 +133,18 @@ read_sector_ebios: read_common: movb (driveno), %dl int $0x13 + popal ret /* * read_partition_table: * Read a partition table (pointed to by %eax), and copy * the partition table into the ptab buffer. - * Preserve registers. + * Clobbers %si, %di, and %cx, other registers preserved. */ ptab = _start+446 read_partition_table: - pushal call read_sector jc 20f movw $bootsec+446, %si @@ -151,7 +152,6 @@ read_partition_table: movw $(16*4/2), %cx rep ; movsw 20: - popal ret /* @@ -173,18 +173,18 @@ scan_partition_table: movw %sp, %bp /* Search for active partitions */ - movw $ptab, %di + movw $ptab, %bx movw $4, %cx xorw %ax, %ax - push %di + push %bx push %cx 5: - testb $0x80, (%di) + testb $0x80, (%bx) jz 6f incw %ax - movw %di, %si + movw %bx, %si 6: - addw $16, %di + addw $16, %bx loopw 5b decw %ax /* Number of active partitions found */ @@ -192,10 +192,10 @@ scan_partition_table: jns too_many_active /* No active partitions found, look for extended partitions */ - popw %di /* %di <- ptab */ + popw %bx /* %bx <- ptab */ popw %cx /* %cx <- 4 */ 7: - movb 4(%di), %al + movb 4(%bx), %al cmpb $0x0f, %al /* 0x0f = Win9x extended */ je 8f andb $~0x80, %al /* 0x85 = Linux extended */ @@ -206,7 +206,7 @@ scan_partition_table: try to scan it. If the scan returns, re-load the current partition table and resume scan. */ 8: - movl 8(%di), %eax /* Partition table offset */ + movl 8(%bx), %eax /* Partition table offset */ movl 20(%bp), %edx /* "Root" */ addl %edx, %eax /* Compute location of new ptab */ andl %edx, %edx /* Is this the MBR? */ @@ -224,7 +224,7 @@ scan_partition_table: /* fall through */ 9: /* Not an extended partition */ - addw $16, %di + addw $16, %bx loopw 7b /* Nothing found, return */ @@ -239,9 +239,7 @@ boot: movl 8(%si), %eax addl 28(%bp), %eax movl %eax, 8(%si) /* Adjust in-memory partition table entry */ - pushw %si call read_sector - popw %si /* ds:si -> partition table entry */ jc disk_error cmpw $0xaa55, (bootsec+510) jne missing_os /* Not a valid boot sector */ |