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-rw-r--r--src/x86_64/tsc-x86_64.s2
1 files changed, 2 insertions, 0 deletions
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