X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?a=blobdiff_plain;ds=inline;f=src%2Fboot%2Fboot2.s;h=2a163e1f650923be53a4d3a3cb8cf93e4d5694a2;hb=f8a1d5e7149556e8afd49612e80c78330a985434;hp=59096acd2b5ce7db337e718d5607b451dc730b9b;hpb=f03c64c0d3c22faa867aaad9243b679f5d1d7819;p=bootcensus

diff --git a/src/boot/boot2.s b/src/boot/boot2.s
index 59096ac..2a163e1 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"
 
@@ -683,15 +685,21 @@ 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