X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?a=blobdiff_plain;f=src%2Fboot%2Fboot2.s;h=719f37e99549e7dbc249344f83170e4dc4a631f8;hb=77450ffb9190c6aa2a04bc23792a143b5886e459;hp=59096acd2b5ce7db337e718d5607b451dc730b9b;hpb=f03c64c0d3c22faa867aaad9243b679f5d1d7819;p=bootcensus

diff --git a/src/boot/boot2.s b/src/boot/boot2.s
index 59096ac..719f37e 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