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[PATCH 3/3] x86/boot: fold branches in video handling code
- To: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 8 Sep 2021 15:24:12 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Wed, 08 Sep 2021 13:24:20 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
Using Jcc to branch around a JMP is necessary only in pre-386 code,
where Jcc is limited to disp8. Use the opposite Jcc directly in two
places. Since it's adjacent, also convert an ORB to TESTB.
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
This is an easy change reducing the overall trampoline size a little.
We're pretty close to needing a 4th page, which I'd prefer to avoid for
as long as we can.
--- a/xen/arch/x86/boot/video.S
+++ b/xen/arch/x86/boot/video.S
@@ -332,8 +332,7 @@ lment: movb $0, (%di)
cmpw $0x656d, (%si) # 'me'
jnz lmhx
cmpw $0x756e, 2(%si) # 'nu'
- jnz lmhx
- jmp listm
+ jz listm
lmhx: xorw %bx, %bx # Else => mode ID in hex
lmhex: lodsb
@@ -401,10 +400,8 @@ mode_set:
cmpb $VIDEO_FIRST_VESA>>8, %ah
jnc check_vesa
- orb %ah, %ah
- jnz setbad
-
- jmp setmenu
+ testb %ah, %ah
+ jz setmenu
setbad: clc
ret
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