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fixed int86 to return correctly from BIOS calls that internally change
[bootcensus]
/
src
/
boot
/
boot2.s
diff --git
a/src/boot/boot2.s
b/src/boot/boot2.s
index
59096ac
..
7067a8f
100644
(file)
--- a/
src/boot/boot2.s
+++ b/
src/boot/boot2.s
@@
-15,6
+15,8
@@
# along with this program. If not, see <https://www.gnu.org/licenses/>.
# this is the second-stage boot loader
# along with this program. If not, see <https://www.gnu.org/licenses/>.
# this is the second-stage boot loader
+# plus some other code that needs to run below 1mb (int86 implementation).
+
.code16
.section .boot2,"ax"
.code16
.section .boot2,"ax"
@@
-613,16
+615,20
@@
e820_looptop:
cmp $0x534d4150, %eax
jnz 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)
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)
- # only care for type 1 (usable ram), otherwise ignore
- cmpl $1, 16(%edi)
- jnz e820_skip
-
# skip areas with 0 size (also clamp size to 4gb)
# test high 32bits
cmpl $0, 12(%edi)
# skip areas with 0 size (also clamp size to 4gb)
# test high 32bits
cmpl $0, 12(%edi)
@@
-683,15
+689,21
@@
detect_mem_e801:
movzx %cx, %eax
# first size is in KB, convert to bytes
shl $10, %eax
movzx %cx, %eax
# first size is in KB, convert to bytes
shl $10, %eax
- mov %eax, 4(%esi)
- cmp $0, %dx
+ jnc 0f
+ # overflow means it's >4GB, clamp to 4GB
+ mov $0xffffffff, %eax
+0: mov %eax, 4(%esi)
incl boot_mem_map_size
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
jz e801_done
movl $0x1000000, 8(%esi)
movzx %dx, %eax
# second size is in 64kb blocks, convert to bytes
shl $16, %eax
- mov %eax, 12(%esi)
+ 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
incl boot_mem_map_size
e801_done:
clc
@@
-751,6
+763,9
@@
rmidt: .short 0x3ff
saved_esp: .long 0
saved_ebp: .long 0
saved_esp: .long 0
saved_ebp: .long 0
+saved_eax: .long 0
+saved_es: .word 0
+saved_ds: .word 0
# drop back to unreal mode to call 16bit interrupt
.global int86
# drop back to unreal mode to call 16bit interrupt
.global int86
@@
-791,17
+806,24
@@
int86:
mov %ebp, saved_ebp
mov 12(%ebp), %esp
popal
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
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
# call 16bit interrupt
int_op: int $0
- mov saved_ebp, %ebp
- mov 12(%ebp), %esp
- add $34, %esp
- pushfw
- pushal
- mov saved_esp, %esp
+ # 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
# re-enable protection
mov %cr0, %eax
# re-enable protection
mov %cr0, %eax
@@
-818,6
+840,18
@@
int_op: int $0
mov %ax, %ss
nop
mov %ax, %ss
nop
+ mov saved_ebp, %ebp
+ mov 12(%ebp), %esp
+ add $38, %esp
+ mov saved_ds, %ax
+ pushw %ax
+ mov saved_es, %ax
+ pushw %ax
+ pushfw
+ mov saved_eax, %eax
+ pushal
+ mov saved_esp, %esp
+
# restore 32bit interrupt descriptor table
lidt (saved_idtr)
sti
# restore 32bit interrupt descriptor table
lidt (saved_idtr)
sti
@@
-829,3
+863,5
@@
int_op: int $0
# buffer used by the track loader ... to load tracks.
.align 16
buffer:
# buffer used by the track loader ... to load tracks.
.align 16
buffer:
+ .global low_mem_buffer
+low_mem_buffer: