Re: Andi, you broke my laptop :-)

["Joerg Roedel" <joerg.roedel@amd.com>]

On Thu, May 10, 2007 at 03:01:44PM +0200, Andi Kleen wrote:
> On Wed, May 09, 2007 at 12:56:16PM -0700, Pete Zaitcev wrote:
> > Hi, Andi:
> > 
> > The attached patch (actually, git show output) makes my Dell 1501 to hang
> > on boot. Sorry, I have no clue why... The culprit is found with git bisect.
> > But yes, it's an AMD MK-36. I use an x86_64 kernel. It is 100% reproducible.
> 
> MK-36? Does it have SVM? 
> 
> Anyways we previously had issues with this being miscompiled, but 
> I thought the latest patch should have been ok. What compiler do you use?
> 
> Can you send me a disassembly listing of arch/x86_64/kernel/time.o?

I debugged this problem a bit and my compiler[1]interprets the =A
constraint as %rax instead of %edx:%eax on x86_64 which causes the
problem. The appended patch provides a workaround for this and fixed the
hang on my machine.

[1] gcc version 4.1.3 20070429 (prerelease) (Debian 4.1.2-5)

Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

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diff --git a/include/asm-i386/alternative.h b/include/asm-i386/alternative.h
index 0f70b37..eb7da54 100644
--- a/include/asm-i386/alternative.h
+++ b/include/asm-i386/alternative.h
@@ -98,6 +98,12 @@ static inline void alternatives_smp_switch(int smp) {}
 		      ".previous" : output : [feat] "i" (feature), ##input)
 
 /*
+ * use this macro(s) if you need more than one output parameter
+ * in alternative_io
+ */
+#define ASM_OUTPUT2(a, b) a, b
+
+/*
  * Alternative inline assembly for SMP.
  *
  * The LOCK_PREFIX macro defined here replaces the LOCK and
diff --git a/include/asm-i386/tsc.h b/include/asm-i386/tsc.h
index 3f3c1fa..62c091f 100644
--- a/include/asm-i386/tsc.h
+++ b/include/asm-i386/tsc.h
@@ -35,14 +35,16 @@ static inline cycles_t get_cycles(void)
 static __always_inline cycles_t get_cycles_sync(void)
 {
 	unsigned long long ret;
-	unsigned eax;
+	unsigned eax, edx;
 
 	/*
   	 * Use RDTSCP if possible; it is guaranteed to be synchronous
  	 * and doesn't cause a VMEXIT on Hypervisors
 	 */
 	alternative_io(ASM_NOP3, ".byte 0x0f,0x01,0xf9", X86_FEATURE_RDTSCP,
-			 	 "=A" (ret), "0" (0ULL) : "ecx", "memory");
+		       ASM_OUTPUT2("=a" (eax), "=d" (edx)),
+		       "a" (0U), "d" (0U) : "ecx", "memory");
+	ret = (((unsigned long long)edx) << 32) | ((unsigned long long)eax);
 	if (ret)
 		return ret;
 
diff --git a/include/asm-x86_64/alternative.h b/include/asm-x86_64/alternative.h
index a09fe85..a094276 100644
--- a/include/asm-x86_64/alternative.h
+++ b/include/asm-x86_64/alternative.h
@@ -103,6 +103,12 @@ static inline void alternatives_smp_switch(int smp) {}
 		      ".previous" : output : [feat] "i" (feature), ##input)
 
 /*
+ * use this macro(s) if you need more than one output parameter
+ * in alternative_io
+ */
+#define ASM_OUTPUT2(a, b) a, b
+
+/*
  * Alternative inline assembly for SMP.
  *
  * The LOCK_PREFIX macro defined here replaces the LOCK and