[gnome-builder] egg: make rdtscp call handle masking core bits

[Christian Hergert <chergert src gnome org>]

commit 68a6694db947482494159afd53edec560f151823
Author: Christian Hergert <christian hergert me>
Date:   Thu Sep 17 02:49:37 2015 -0700

    egg: make rdtscp call handle masking core bits
    
    Only the bottom 12 bits contain the cpu identifier. The following bits are
    the numa node.

 contrib/egg/egg-counter.h |   11 ++++++++---
 1 files changed, 8 insertions(+), 3 deletions(-)
---
diff --git a/contrib/egg/egg-counter.h b/contrib/egg/egg-counter.h
index 42e62ba..ca27fe8 100644
--- a/contrib/egg/egg-counter.h
+++ b/contrib/egg/egg-counter.h
@@ -146,9 +146,14 @@ G_BEGIN_DECLS
   static inline guint
   egg_get_current_cpu (void)
   {
-    guint cpu;
-    __builtin_ia32_rdtscp (&cpu);
-    return cpu;
+    /*
+     * This extracts the IA32_TSC_AUX into the ecx register. On Linux,
+     * that value contains a value with the bottom 12 bits being the
+     * cpu identifier, and the next 10 bits being the node group.
+     */
+    guint aux;
+    __builtin_ia32_rdtscp (&aux);
+    return aux & 0xFFF;
   }
 #elif defined(__linux__)
 # ifndef _GNU_SOURCE