[PATCH v4 0/2] Clear .bss for PV guests

[PATCH v4 0/2] Clear .bss for PV guests

[Boris Ostrovsky]

PV guests need to have their .bss zeroed out since it is not guaranteed
to be cleared by Xen's domain builder (even if it is done so currently)

v4:
* Better use of mode-selecting macros.
* Drop stable tag.
* Update commit message for patch 1.

Boris Ostrovsky (2):
  xen/x86: Zero out .bss for PV guests
  xen/x86: Drop mode-selecting ifdefs in startup_xen()

 arch/x86/xen/xen-head.S | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

-- 
2.1.0

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

[Boris Ostrovsky]

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

[PATCH v4 2/2] xen/x86: Drop mode-selecting ifdefs in startup_xen()

[Boris Ostrovsky]

Use asm/asm.h macros instead.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
 arch/x86/xen/xen-head.S | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index 5c63d2d..de93b20 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -47,13 +47,9 @@ ENTRY(startup_xen)
 	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
-#else
-	mov %rsi,xen_start_info
-	mov $init_thread_union+THREAD_SIZE,%rsp
-#endif
+	mov %_ASM_SI, xen_start_info
+	mov $init_thread_union+THREAD_SIZE, %_ASM_SP
+
 	jmp xen_start_kernel
 
 	__FINIT
-- 
2.1.0

Re: [Xen-devel] [PATCH v4 0/2] Clear .bss for PV guests

[David Vrabel]

On 26/02/16 19:02, Boris Ostrovsky wrote:
> PV guests need to have their .bss zeroed out since it is not guaranteed
> to be cleared by Xen's domain builder (even if it is done so currently)

Applied to for-linus-4.6, thanks.

David