linux-kernel - [PATCH] xen/x86: Zero out .bss for PV guests

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Date:	Mon, 22 Feb 2016 17:06:07 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	konrad.wilk@...cle.com, david.vrabel@...rix.com
Cc:	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
	mcgrof@...nel.org, Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: [PATCH] xen/x86: Zero out .bss for PV guests

Baremetal kernels clear .bss early in the boot. Since Xen PV guests don't
excecute that early code they should do it too.

(Since we introduce macros for specifying 32- and 64-bit registers we
can get rid of ifdefs in startup_xen())

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
---
 arch/x86/xen/xen-head.S | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index b65f59a..2af87d1 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -35,16 +35,31 @@
 #define PVH_FEATURES (0)
 #endif
 
-	__INIT
-ENTRY(startup_xen)
-	cld
 #ifdef CONFIG_X86_32
-	mov %esi,xen_start_info
-	mov $init_thread_union+THREAD_SIZE,%esp
+#define REG(register)	%e##register
+#define WSIZE_SHIFT	2
+#define STOS		stosl
 #else
-	mov %rsi,xen_start_info
-	mov $init_thread_union+THREAD_SIZE,%rsp
+#define REG(register)	%r##register
+#define WSIZE_SHIFT	3
+#define STOS		stosq
 #endif
+
+	__INIT
+ENTRY(startup_xen)
+	cld
+
+	/* Clear .bss */
+	xor REG(ax),REG(ax)
+	mov $__bss_start,REG(di)
+	mov $__bss_stop,REG(cx)
+	sub REG(di),REG(cx)
+	shr $WSIZE_SHIFT,REG(cx)
+	rep STOS
+
+	mov REG(si),xen_start_info
+	mov $init_thread_union+THREAD_SIZE,REG(sp)
+
 	jmp xen_start_kernel
 
 	__FINIT
-- 
2.1.0