X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?p=bootcensus;a=blobdiff_plain;f=src%2Fboot%2Fboot2.s;h=5aeebaa66a0e54dd2c043bbec8620a808d5c8c32;hp=59918b8358341f30d99edc122c1514e789651329;hb=6ddbba6fc0185f6aaf64c661c303549eb088010f;hpb=d1e8a437c1fab4535f82c4c214ec3330ac32e48d diff --git a/src/boot/boot2.s b/src/boot/boot2.s index 59918b8..5aeebaa 100644 --- a/src/boot/boot2.s +++ b/src/boot/boot2.s @@ -15,6 +15,8 @@ # along with this program. If not, see . # this is the second-stage boot loader +# plus some other code that needs to run below 1mb (int86 implementation). + .code16 .section .boot2,"ax" @@ -34,6 +36,9 @@ # enable A20 address line call enable_a20 + # detect available memory + call detect_memory + # load the whole program into memory starting at 1MB call load_main @@ -225,7 +230,7 @@ ldloop: # just in case we were loaded from floppy, turn all floppy motors off mov $0x3f2, %dx in %dx, %al - and $0xf0, %al + and $0xf, %al out %al, %dx mov $10, %ax @@ -553,5 +558,319 @@ kbc_wait_write: numbuf: .space 16 + +detect_memory: + mov $memdet_e820_msg, %esi + call putstr + call detect_mem_e820 + jnc memdet_done + mov $rdfail_msg, %esi + call putstr + + mov $memdet_e801_msg, %esi + call putstr + call detect_mem_e801 + jnc memdet_done + mov $rdfail_msg, %esi + call putstr + + mov $memdet_88_msg, %esi + call putstr + call detect_mem_88 + jnc memdet_done + mov $rdfail_msg, %esi + call putstr + + # just panic... + mov $memdet_fail_msg, %esi + call putstr +0: hlt + jmp 0b + +memdet_done: + mov $rdok_msg, %esi + call putstr + ret + +memdet_fail_msg: .ascii "Failed to detect available memory!\n" + .ascii "Please file a bug report: https://github.com/jtsiomb/pcboot/issues\n" + .asciz " or contact me through email: nuclear@member.fsf.org\n" +memdet_e820_msg: .asciz "Detecting RAM (BIOS 15h/0xe820)... " +memdet_e801_msg: .asciz "Detecting RAM (BIOS 15h/0xe801)... " +memdet_88_msg: .asciz "Detecting RAM (BIOS 15h/0x88, max 64mb)... " + + # detect extended memory using BIOS call 15h/e820 +detect_mem_e820: + movl $0, boot_mem_map_size + + mov $buffer, %edi + xor %ebx, %ebx + mov $0x534d4150, %edx + +e820_looptop: + mov $0xe820, %eax + mov $24, %ecx + int $0x15 + jc e820_fail + cmp $0x534d4150, %eax + jnz e820_fail + + # skip areas starting above 4GB as we won't be able to use them + cmpl $0, 4(%edi) + jnz e820_skip + + # only care for type 1 (usable ram), otherwise ignore + cmpl $1, 16(%edi) + jnz e820_skip + + mov buffer, %eax + mov $boot_mem_map, %esi + mov boot_mem_map_size, %ebp + # again, that's [ebp * 8 + esi] + mov %eax, (%esi,%ebp,8) + + # skip areas with 0 size (also clamp size to 4gb) + # test high 32bits + cmpl $0, 12(%edi) + jz e820_highzero + # high part is non-zero, make low part ffffffff + xor %eax, %eax + not %eax + jmp 0f + +e820_highzero: + # if both high and low parts are zero, ignore + mov 8(%edi), %eax + cmpl $0, %eax + jz e820_skip + +0: mov %eax, 4(%esi,%ebp,8) + incl boot_mem_map_size + +e820_skip: + # terminate the loop if ebx was reset to 0 + cmp $0, %ebx + jz e820_done + jmp e820_looptop + +e820_done: + clc + ret + +e820_fail: + # if size > 0, then it's not a failure, just the end + cmpl $0, boot_mem_map_size + jnz e820_done + + stc + ret + + + # detect extended memory using BIOS call 15h/e801 +detect_mem_e801: + mov $boot_mem_map, %esi + mov boot_mem_map_size, %ebp + movl $0, (%ebp) + + xor %cx, %cx + xor %dx, %dx + mov $0xe801, %ax + int $0x15 + jc e801_fail + + cmp $0, %cx + jnz 0f + cmp $0, %ax + jz e801_fail + mov %ax, %cx + mov %bx, %dx + +0: movl $0x100000, (%esi) + movzx %cx, %eax + # first size is in KB, convert to bytes + shl $10, %eax + jnc 0f + # overflow means it's >4GB, clamp to 4GB + mov $0xffffffff, %eax +0: mov %eax, 4(%esi) + incl boot_mem_map_size + cmp $0, %dx + jz e801_done + movl $0x1000000, 8(%esi) + movzx %dx, %eax + # second size is in 64kb blocks, convert to bytes + shl $16, %eax + jnc 0f + # overflow means it's >4GB, clamp to 4GB + mov $0xffffffff, %eax +0: mov %eax, 12(%esi) + incl boot_mem_map_size +e801_done: + clc + ret +e801_fail: + stc + ret + +detect_mem_88: + # reportedly some BIOS implementations fail to clear CF on success + clc + mov $0x88, %ah + int $0x15 + jc x88_fail + + cmp $0, %ax + jz x88_fail + + # ax has size in KB, convert to bytes in eax + and $0xffff, %eax + shl $10, %eax + + mov $boot_mem_map, %esi + movl $0x100000, (%esi) + mov %eax, 4(%esi) + + movl $1, boot_mem_map_size + clc + ret + +x88_fail: + stc + ret + + + .global boot_mem_map_size +boot_mem_map_size: .long 0 + .global boot_mem_map +boot_mem_map: .space 128 + + +# this is not boot loader code. It's called later on by the main kernel +# code in 32bit protected mode. It's placed here because it needs to be +# located in base memory as it returns and runs in real mode. + .code32 + .align 4 + # place to save the protected mode IDTR pseudo-descriptor + # with sidt, so that it can be restored before returning + .short 0 +saved_idtr: +idtlim: .short 0 +idtaddr:.long 0 + # real mode IDTR pseudo-descriptor pointing to the IVT at addr 0 + .short 0 +rmidt: .short 0x3ff + .long 0 + +saved_esp: .long 0 +saved_ebp: .long 0 +saved_eax: .long 0 +saved_es: .word 0 +saved_ds: .word 0 +saved_flags: .word 0 + + # drop back to unreal mode to call 16bit interrupt + .global int86 +int86: + push %ebp + mov %esp, %ebp + pushal + cli + # save protected mode IDTR and replace it with the real mode vectors + sidt (saved_idtr) + lidt (rmidt) + + # modify the int instruction. do this here before the + # cs-load jumps, to let them flush the instruction cache + mov $int_op, %ebx + movb 8(%ebp), %al + movb %al, 1(%ebx) + + # long jump to load code selector for 16bit code (6) + ljmp $0x30,$0f +0: + .code16 + # disable protection + mov %cr0, %eax + and $0xfffe, %ax + mov %eax, %cr0 + # load cs <- 0 + ljmp $0,$0f +0: # zero data segments + xor %ax, %ax + mov %ax, %ds + mov %ax, %es + mov %ax, %ss + nop + + # load registers from the int86regs struct + # point esp to the regs struct to load registers with popa/popf + mov %esp, saved_esp + mov %ebp, saved_ebp + mov 12(%ebp), %esp + popal + popfw + pop %es + pop %ds + # ignore fs and gs for now, don't think I'm going to need them + mov saved_esp, %esp + + # move to the real-mode stack, accessible from ss=0 + # just in case the BIOS call screws up our unreal mode + mov $0x7be0, %esp + + # call 16bit interrupt +int_op: int $0 + # BIOS call might have enabled interrupts, cli for good measure + cli + + # save all registers that we'll clobber before having the + # chance to populate the int86regs structure + mov %eax, saved_eax + mov %ds, saved_ds + mov %es, saved_es + pushfw + pop %ax + mov %ax, saved_flags + + # re-enable protection + mov %cr0, %eax + or $1, %ax + mov %eax, %cr0 + # long jump to load code selector for 32bit code (1) + ljmp $0x8,$0f +0: + .code32 + # set data selector (2) to all segment regs + mov $0x10, %ax + mov %ax, %ds + mov %ax, %es + mov %ax, %ss + nop + + # point the esp to our regs struct, to fill it with pusha/pushf + mov saved_ebp, %ebp + mov 12(%ebp), %esp + add $38, %esp + mov saved_ds, %ax + pushw %ax + mov saved_es, %ax + pushw %ax + mov saved_flags, %ax + pushw %ax + mov saved_eax, %eax + pushal + mov saved_esp, %esp + + # restore 32bit interrupt descriptor table + lidt (saved_idtr) + sti + popal + pop %ebp + ret + + + # buffer used by the track loader ... to load tracks. .align 16 buffer: + .global low_mem_buffer +low_mem_buffer: