diff options
Diffstat (limited to 'bootasm.S')
| -rw-r--r-- | bootasm.S | 11 |
1 files changed, 8 insertions, 3 deletions
@@ -13,7 +13,7 @@ .code16 # Assemble for 16-bit mode .globl start start: - cli # Disable interrupts + cli # BIOS enabled interrupts ; disable # Set up the important data segment registers (DS, ES, SS). xorw %ax,%ax # Segment number zero @@ -45,7 +45,8 @@ seta20.2: # Switch from real to protected mode, using a bootstrap GDT # and segment translation that makes virtual addresses # identical to physical addresses, so that the - # effective memory map does not change during the switch. + # effective memory map does not change after subsequent + # loads of segment registers. lgdt gdtdesc movl %cr0, %eax orl $CR0_PE, %eax @@ -57,7 +58,11 @@ seta20.2: # default to 32 bits after this jump. ljmp $(SEG_KCODE<<3), $start32 -.code32 # Assemble for 32-bit mode +# tell the assembler to generate 0x66 prefixes for 16-bit +# instructions like movw, and to generate 32-bit immediate +# addresses. +.code32 + start32: # Set up the protected-mode data segment registers movw $(SEG_KDATA<<3), %ax # Our data segment selector |