x86: explicitly mark __initdata variables as used when building with clang.

This stops LLVM from replacing it with a different, auto-generated
variable as part of an optimization.  (The auto-generated variable
ends up in the normal data section.)

Remove stray __read_mostly annotations on declarations that this unmasked.

Signed-off-by: Tim Deegan <tim@xen.org>
Acked-by: Keir Fraser <keir@xen.org>
Committed-by: Tim Deegan <tim@xen.org>

xen/arch/x86/oprofile/op_x86_model.h

@@ -53,6 +53,6 @@ extern struct op_x86_model_spec const op_amd_fam15h_spec;
 void arch_perfmon_setup_counters(void);
 
 extern int ppro_has_global_ctrl;
-extern struct op_x86_model_spec const *__read_mostly model;
+extern struct op_x86_model_spec const *model;
 
 #endif /* OP_X86_MODEL_H */

xen/include/acpi/cpufreq/cpufreq.h

@@ -22,7 +22,7 @@
 
 DECLARE_PER_CPU(spinlock_t, cpufreq_statistic_lock);
 
-extern bool_t __read_mostly cpufreq_verbose;
+extern bool_t cpufreq_verbose;
 
 struct cpufreq_governor;
 

xen/include/xen/compiler.h

@@ -14,7 +14,13 @@
 #define always_inline __inline__ __attribute__ ((always_inline))
 #define noinline      __attribute__((noinline))
 
+#ifdef __clang__
+/* Clang can replace some vars with new automatic ones that go in .data;
+ * mark all explicit-segment vars 'used' to prevent that. */
+#define __section(s)      __attribute_used__ __attribute__((__section__(s)))
+#else
 #define __section(s)      __attribute__((__section__(s)))
+#endif
 #define __used_section(s) __attribute_used__ __attribute__((__section__(s)))
 #define __text_section(s) __attribute__((__section__(s)))