X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?p=bootcensus;a=blobdiff_plain;f=src%2Fboot%2Fboot2.s;h=f782d7ef50aca782b0cb16a80bb692e89d3b02dd;hp=59096acd2b5ce7db337e718d5607b451dc730b9b;hb=6e5ec45bc9c248586ec797646158b4caa3aa9d68;hpb=f03c64c0d3c22faa867aaad9243b679f5d1d7819

diff --git a/src/boot/boot2.s b/src/boot/boot2.s
index 59096ac..f782d7e 100644
--- 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
+# plus some other code that needs to run below 1mb (int86 implementation).
+
 	.code16
 	.section .boot2,"ax"
 
@@ -613,16 +615,20 @@ e820_looptop:
 	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)
 
-	# 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)
@@ -683,15 +689,21 @@ detect_mem_e801:
 	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
+	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
-	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
@@ -751,6 +763,10 @@ rmidt:	.short 0x3ff
 
 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
@@ -763,7 +779,7 @@ int86:
 	sidt (saved_idtr)
 	lidt (rmidt)
 
-	# modify the int instruction do this here before the
+	# 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
@@ -787,21 +803,34 @@ int86:
 	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
 
-	mov saved_ebp, %ebp
-	mov 12(%ebp), %esp
-	add $34, %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
 	pushfw
-	pushal
-	mov saved_esp, %esp
+	pop %ax
+	mov %ax, saved_flags
 
 	# re-enable protection
 	mov %cr0, %eax
@@ -818,6 +847,20 @@ int_op:	int $0
 	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
@@ -829,3 +872,5 @@ int_op:	int $0
 	# buffer used by the track loader ... to load tracks.
 	.align 16
 buffer:
+	.global low_mem_buffer
+low_mem_buffer: