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| author | H. Peter Anvin <hpa@zytor.com> | 2007-07-11 15:21:54 -0700 |
|---|---|---|
| committer | H. Peter Anvin <hpa@zytor.com> | 2007-07-11 15:21:54 -0700 |
| commit | 879ae26f225f4d16ff75f7f380f14f12e95051f6 (patch) | |
| tree | 7517ad46a863079b2cb505ff193a1d5e0b8047d9 /mbr | |
| parent | 6639ea5c992e99aa7bd1182d2d9e12997be8697e (diff) | |
| download | syslinux-879ae26f225f4d16ff75f7f380f14f12e95051f6.tar.gz | |
Shave an additional ~7 bytes off the MBR
Diffstat (limited to 'mbr')
| -rw-r--r-- | mbr/mbr.S | 32 |
1 files changed, 16 insertions, 16 deletions
@@ -98,9 +98,8 @@ next: mulw %cx /* Heads*sectors -> sectors per cylinder */ pushw %ax /* Save sectors/cylinder on the stack */ - xorl %eax, %eax - pushl %eax /* Base */ - pushl %eax /* Root */ + xorl %eax, %eax /* Base */ + xorl %edx, %edx /* Root: %edx <- 0 */ call scan_partition_table /* If we get here, we have no OS */ @@ -158,15 +157,19 @@ read_partition_table: /* * scan_partition_table: * Scan a partition table currently loaded in the partition table - * area. Preserve 16-bit registers. + * area. Preserve all registers. * - * On stack: - * 18(%bp) - root (offset from MBR, or 0 for MBR) - * 22(%bp) - base (location of this partition table) + * On entry: + * %eax - base (location of this partition table) + * %edx - root (offset from MBR, or 0 for MBR) + * + * These get pushed into stack slots: + * 28(%bp) - %eax - base + * 20(%bp) - %edx - root */ scan_partition_table: - pusha + pushal movw %sp, %bp /* Search for active partitions */ @@ -175,7 +178,7 @@ scan_partition_table: xorw %ax, %ax 5: testb $0x80, (%di) - jz 6f + jz 6f incw %ax movw %di, %si 6: @@ -203,21 +206,18 @@ scan_partition_table: partition table and resume scan. */ 8: movl 8(%di), %eax /* Partition table offset */ - movl 18(%bp), %edx /* "Root" */ + movl 20(%bp), %edx /* "Root" */ addl %edx, %eax /* Compute location of new ptab */ andl %edx, %edx /* Is this the MBR? */ jnz 10f movl %eax, %edx /* Offset -> root if this was MBR */ 10: - pushl %eax /* Push new base */ - pushl %edx /* Push new root */ call read_partition_table - jc 11f + jc 11f call scan_partition_table 11: - addw $8, %sp /* This returned, so we need to reload the current partition table */ - movl 22(%bp), %eax + movl 28(%bp), %eax call read_partition_table /* fall through */ @@ -227,7 +227,7 @@ scan_partition_table: loopw 7b /* Nothing found, return */ - popa + popal ret /* |