Fail the build if NR_hypercalls is not a power of two.

Making this requirement clearer originally suggested by
Muli Ben Yehuda.

Signed-off-by: Keir Fraser <keir@xensource.com>

diff --git a/xen/include/asm-x86/config.h b/xen/include/asm-x86/config.h
index 23aabeb2b97fa9e25268d616dcf469758d86949f..35efb1ba63b875330fda7300ad7956bde084c1a1 100644 (file)
--- a/xen/include/asm-x86/config.h
+++ b/xen/include/asm-x86/config.h
@@ -65,8 +65,13 @@
 
 #define barrier() __asm__ __volatile__("": : :"memory")
 
+/* A power-of-two value greater than or equal to number of hypercalls. */
 #define NR_hypercalls 32
 
+#if NR_hypercalls & (NR_hypercalls - 1)
+#error "NR_hypercalls must be a power-of-two value"
+#endif
+
 #ifndef NDEBUG
 #define MEMORY_GUARD
 #ifdef __x86_64__