linux-kernel - Re: [Xen-devel] Re: [PATCH] xen: Disable stack protector for irq helper

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Date:	Tue, 06 Oct 2009 12:01:12 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Bastian Blank <bastian@...di.eu.org>,
	Ingo Molnar <mingo@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Stable Kernel <stable@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Xen-devel <xen-devel@...ts.xensource.com>
Subject: Re: [Xen-devel] Re: [PATCH] xen: Disable stack protector for irq
 helper

On 10/05/09 20:30, Bastian Blank wrote:
> The original version saves ecx, but not edx. Both are official
> caller-saved registers.
>   

Hm.  It doesn't save edx because that can be half of a 64-bit return
value, and in general both eax and edx are marked clobbered.  Except one
place; does the patch below help?

>> Besides, most of the code in that file isn't used unless you're using a
>> very old version of Xen; it will generally prefer to use the ones in
>> xen-asm_X.S.
>>     
> Well, my call stack say something different. It crashs during early
> startup without a console. The modifications to the function pointers is
> done much later.

You're right.  But you're holding out on me; can I see your backtrace? 
And the disassembly of the troublesome code (both the Xen function and
the calling function)?

Thanks,
    J

From: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Date: Tue, 6 Oct 2009 11:36:44 -0700
Subject: [PATCH] x86/paravirt: use normal calling sequences for irq enable/disable etc

For historical reasons irq enable/disable/save/restore had special
calling sequences to make them more efficient.  With the more
recent introduction of higher-level and more general optimisations
this is no longer necessary so we can just use the normal PVOP_
macros.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index e19ffe3..e8420a2 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -863,42 +863,22 @@ static __always_inline void __raw_spin_unlock(struct raw_spinlock *lock)
 
 static inline unsigned long __raw_local_save_flags(void)
 {
-	unsigned long f;
-
-	asm volatile(paravirt_alt(PARAVIRT_CALL)
-		     : "=a"(f)
-		     : paravirt_type(pv_irq_ops.save_fl),
-		       paravirt_clobber(CLBR_EAX)
-		     : "memory", "cc");
-	return f;
+	return PVOP_CALLEE0(unsigned long, pv_irq_ops.save_fl);
 }
 
 static inline void raw_local_irq_restore(unsigned long f)
 {
-	asm volatile(paravirt_alt(PARAVIRT_CALL)
-		     : "=a"(f)
-		     : PV_FLAGS_ARG(f),
-		       paravirt_type(pv_irq_ops.restore_fl),
-		       paravirt_clobber(CLBR_EAX)
-		     : "memory", "cc");
+	PVOP_VCALLEE1(pv_irq_ops.restore_fl, f);
 }
 
 static inline void raw_local_irq_disable(void)
 {
-	asm volatile(paravirt_alt(PARAVIRT_CALL)
-		     :
-		     : paravirt_type(pv_irq_ops.irq_disable),
-		       paravirt_clobber(CLBR_EAX)
-		     : "memory", "eax", "cc");
+	PVOP_VCALLEE0(pv_irq_ops.irq_disable);
 }
 
 static inline void raw_local_irq_enable(void)
 {
-	asm volatile(paravirt_alt(PARAVIRT_CALL)
-		     :
-		     : paravirt_type(pv_irq_ops.irq_enable),
-		       paravirt_clobber(CLBR_EAX)
-		     : "memory", "eax", "cc");
+	PVOP_VCALLEE0(pv_irq_ops.irq_enable);
 }
 
 static inline unsigned long __raw_local_irq_save(void)
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index b9bb5e8..0b97706 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -612,8 +612,8 @@ int paravirt_disable_iospace(void);
 		       VEXTRA_CLOBBERS,					\
 		       pre, post, ##__VA_ARGS__)
 
-#define __PVOP_VCALLEESAVE(rettype, op, pre, post, ...)			\
-	____PVOP_CALL(rettype, op.func, CLBR_RET_REG,			\
+#define __PVOP_VCALLEESAVE(op, pre, post, ...)				\
+	____PVOP_VCALL(op.func, CLBR_RET_REG,				\
 		      PVOP_VCALLEE_CLOBBERS, ,				\
 		      pre, post, ##__VA_ARGS__)
 


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