x86: fix get_cpu_info() when built with clang

Clang understands the GCCism in use here, but still complains that sp is
unintialised.  In such cases, resort to the older version of this code, which
directly reads %rsp into the temporary variable.

Note that we still keep the GCCism in the default case, as it causes GCC to
create rather better assembly.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/include/asm-x86/current.h b/xen/include/asm-x86/current.h
index f011d2d2a0e456aa6f5396dbf4c1a6e14d36ae75..15b99ff8c0bd5aabf9962f07f700e66223474e56 100644 (file)
--- a/xen/include/asm-x86/current.h
+++ b/xen/include/asm-x86/current.h
@@ -47,7 +47,13 @@ struct cpu_info {
 
 static inline struct cpu_info *get_cpu_info(void)
 {
+#ifdef __clang__
+    /* Clang complains that sp in the else case is not initialised. */
+    unsigned long sp;
+    asm ( "mov %%rsp, %0" : "=r" (sp) );
+#else
     register unsigned long sp asm("rsp");
+#endif
 
     return (struct cpu_info *)((sp & ~(STACK_SIZE-1)) + STACK_SIZE) - 1;
 }