diff options
| -rw-r--r-- | bootasm.S | 22 |
1 files changed, 9 insertions, 13 deletions
@@ -54,16 +54,15 @@ seta20.2: movb $0xdf,%al # Enable outb %al,$0x60 # A20 - # Switch from real to protected mode - # The descriptors in our GDT allow all physical memory to be accessed. - # Furthermore, the descriptors have base addresses of 0, so that the - # segment translation is a NOP, ie. virtual addresses are identical to - # their physical addresses. With this setup, immediately after - # enabling protected mode it will still appear to this code - # that it is running directly on physical memory with no translation. - # This initial NOP-translation setup is required by the processor - # to ensure that the transition to protected mode occurs smoothly. - +# Switch from real to protected mode +# The descriptors in our GDT allow all physical memory to be accessed. +# Furthermore, the descriptors have base addresses of 0, so that the +# segment translation is a NOP, ie. virtual addresses are identical to +# their physical addresses. With this setup, immediately after +# enabling protected mode it will still appear to this code +# that it is running directly on physical memory with no translation. +# This initial NOP-translation setup is required by the processor +# to ensure that the transition to protected mode occurs smoothly. real_to_prot: cli # Mandatory since we dont set up an IDT lgdt gdtdesc # load GDT -- mandatory in protected mode @@ -85,19 +84,16 @@ protcseg: movw %ax, %fs # -> FS movw %ax, %gs # -> GS movw %ax, %ss # -> SS: Stack Segment - call cmain # finish the boot load from C. # cmain() should not return spin: jmp spin # ..but in case it does, spin - .p2align 2 # force 4 byte alignment gdt: SEG_NULLASM # null seg SEG_ASM(STA_X|STA_R, 0x0, 0xffffffff) # code seg SEG_ASM(STA_W, 0x0, 0xffffffff) # data seg - gdtdesc: .word 0x17 # sizeof(gdt) - 1 .long gdt # address gdt |