From 05f68565cc5513223937eae620d9c7d676eff854 Mon Sep 17 00:00:00 2001
From: Paul Davis <paul@linuxaudiosystems.com>
Date: Thu, 31 Dec 2009 17:53:10 +0000
Subject: asm fixes for FPU::FPU() back ported from 3.0

git-svn-id: svn://localhost/ardour2/branches/2.0-ongoing@6421 d708f5d6-7413-0410-9779-e7cbd77b26cf
---
 libs/pbd/fpu.cc | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

(limited to 'libs')

diff --git a/libs/pbd/fpu.cc b/libs/pbd/fpu.cc
index ffb88714f6..a55166b139 100644
--- a/libs/pbd/fpu.cc
+++ b/libs/pbd/fpu.cc
@@ -21,6 +21,12 @@ FPU::FPU ()
 
 #else
 	
+	/* asm notes: although we explicitly save&restore ebx/rbx (stack pointer), we must tell
+	   gcc that ebx,rbx is clobbered so that it doesn't try to use it as an intermediate
+	   register when storing edx/rdx. gcc 4.3 didn't make this "mistake", but gcc 4.4
+	   does, at least on x86_64.
+	*/
+	
 #ifndef USE_X86_64_ASM
 	asm volatile (
 		"mov $1, %%eax\n"
@@ -30,7 +36,7 @@ FPU::FPU ()
 		"popl %%ebx\n"
 		: "=r" (cpuflags)
 		: 
-		: "%eax", "%ecx", "%edx", "memory"
+		: "%eax", "%ebx", "%ecx", "%edx"
 		);
 	
 #else
@@ -43,7 +49,7 @@ FPU::FPU ()
 		"popq %%rbx\n"
 		: "=r" (cpuflags)
 		: 
-		: "%rax", "%rcx", "%rdx", "memory"
+		: "%rax", "%rbx", "%rcx", "%rdx"
 		);
 
 #endif /* USE_X86_64_ASM */
@@ -69,6 +75,8 @@ FPU::FPU ()
 			error << _("cannot allocate 16 byte aligned buffer for h/w feature detection") << endmsg;
 		} else {
 			
+			memset (fxbuf, 0, 512);
+
 			asm volatile (
 				"fxsave (%0)"
 				:
-- 
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