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[PATCH v4 1/2] xen/x86: Zero out .bss for PV guests

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ELF spec is unclear about whether .bss must me cleared by the loader.
Currently the domain builder does it when loading the guest but because
it is not (or rather may not be) guaranteed we should zero it out
explicitly.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
 arch/x86/xen/xen-head.S | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index b65f59a..5c63d2d 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -38,6 +38,15 @@
 	__INIT
 ENTRY(startup_xen)
 	cld
+
+	/* Clear .bss */
+	xor %eax,%eax
+	mov $__bss_start, %_ASM_DI
+	mov $__bss_stop, %_ASM_CX
+	sub %_ASM_DI, %_ASM_CX
+	shr $__ASM_SEL(2, 3), %_ASM_CX
+	rep __ASM_SIZE(stos)
+
 #ifdef CONFIG_X86_32
 	mov %esi,xen_start_info
 	mov $init_thread_union+THREAD_SIZE,%esp
-- 
2.1.0

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[PATCH v4 0/2] Clear .bss for PV guests Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-02-26 20:10 +0100
  [PATCH v4 2/2] xen/x86: Drop mode-selecting ifdefs in startup_xen() Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-02-26 20:10 +0100
  [PATCH v4 1/2] xen/x86: Zero out .bss for PV guests Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-02-26 20:10 +0100
  Re: [Xen-devel] [PATCH v4 0/2] Clear .bss for PV guests David Vrabel <david.vrabel@citrix.com> - 2016-03-03 17:30 +0100

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