From: Andrew Cooper <andrew.cooper3@citrix.com>
Date: Wed, 8 Jan 2020 13:11:13 +0000 (+0000)
Subject: x86/boot: Simplify BSS zeroing
X-Git-Tag: archive/raspbian/4.14.0+80-gd101b417b7-1+rpi1^2~63^2~913
X-Git-Url: https://dgit.raspbian.org/%22http:/www.example.com/cgi/%22https:/%22bookmarks://%22/%22http:/www.example.com/cgi/%22https:/%22bookmarks:/%22?a=commitdiff_plain;h=c6c63b6dbffcdf32a59efa1fd6e578437fba06ff;p=xen.git

x86/boot: Simplify BSS zeroing

There is no need to load a non-flat %es to zero the BSS.  Use sym_esi()
instead, which is easier to follow, faster (avoids two segment loads) and
doesn't require use of the stack.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---

diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index 8d0ffbd1b0..c730810461 100644
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -617,16 +617,12 @@ trampoline_setup:
         jnz     1f
 
         /* Initialize BSS (no nasty surprises!). */
-        mov     $sym_offs(__bss_start),%edi
-        mov     $sym_offs(__bss_end),%ecx
-        push    %fs
-        pop     %es
+        lea     sym_esi(__bss_start), %edi
+        lea     sym_esi(__bss_end), %ecx
         sub     %edi,%ecx
         xor     %eax,%eax
         shr     $2,%ecx
         rep stosl
-        push    %ds
-        pop     %es
 
 1:
         /* Interrogate CPU extended features via CPUID. */