From 9bfbf7832dd379a4a006d236fbeda27be7e13928 Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@gmail.com>
Date: Mon, 21 Sep 2009 03:48:30 +0000
Subject: Make `cpuid' do the same thing for every sandglass_get_tsc() call.

---
 src/x86_64/tsc-x86_64.s | 2 ++
 1 file changed, 2 insertions(+)

(limited to 'src/x86_64')

diff --git a/src/x86_64/tsc-x86_64.s b/src/x86_64/tsc-x86_64.s
index 52f02c2..e710891 100644
--- a/src/x86_64/tsc-x86_64.s
+++ b/src/x86_64/tsc-x86_64.s
@@ -28,11 +28,13 @@
         .type sandglass_get_tsc, @function
 sandglass_get_tsc:
         movq %rbx, %rdi         /* Callee-save register, clobbered by cpuid */
+        xorl %eax, %eax         /* Make cpuid do a consistent operation */
         cpuid                   /* Serialize */
         rdtsc                   /* Read time stamp counter */
         shlq $32, %rdx
         orq %rdx, %rax
         movq %rax, %rsi
+        xorl %eax, %eax
         cpuid                   /* Serialize again */
         movq %rsi, %rax
         movq %rdi, %rbx
-- 
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