kern/macros: update

Add comments to power-of-two alignment macros, remove functionality made
standard in C11, remove the __alias macro, add the __noinline macro.

1 files changed, 19 insertions, 12 deletions

diff --git a/kern/macros.h b/kern/macros.h
index 743bdc0d..6259dcee 100644
--- a/kern/macros.h
+++ b/kern/macros.h
@@ -24,9 +24,9 @@
 #ifndef _KERN_MACROS_H
 #define _KERN_MACROS_H
 
-#ifndef __ASSEMBLER__
-#include <stddef.h>
-#endif /* __ASSEMBLER__ */
+#if !defined(__GNUC__) || (__GNUC__ < 4)
+#error "GCC 4+ required"
+#endif
 
 /*
  * Attributes for variables that are mostly read and seldom changed.
@@ -56,29 +56,36 @@
 
 #define P2ALIGNED(x, a)     (((x) & ((a) - 1)) == 0)
 #define ISP2(x)             P2ALIGNED(x, x)
-#define P2ALIGN(x, a)       ((x) & -(a))
-#define P2ROUND(x, a)       (-(-(x) & -(a)))
-#define P2END(x, a)         (-(~(x) & -(a)))
+#define P2ALIGN(x, a)       ((x) & -(a))        /* decreases if not aligned */
+#define P2ROUND(x, a)       (-(-(x) & -(a)))    /* increases if not aligned */
+#define P2END(x, a)         (-(~(x) & -(a)))    /* always increases */
 
 #define structof(ptr, type, member) \
     ((type *)((char *)(ptr) - offsetof(type, member)))
 
-#define alignof(x)          __alignof__(x)
-
 #define likely(expr)        __builtin_expect(!!(expr), 1)
 #define unlikely(expr)      __builtin_expect(!!(expr), 0)
 
 #define barrier()           asm volatile("" : : : "memory")
 
-#define __noreturn          __attribute__((noreturn))
-#define __aligned(x)        __attribute__((aligned(x)))
+/*
+ * The following macros may be provided by the C environment.
+ */
+
+#ifndef __noinline
+#define __noinline          __attribute__((noinline))
+#endif
 
 #ifndef __always_inline
 #define __always_inline     inline __attribute__((always_inline))
-#endif /* __attribute__ */
+#endif
 
+#ifndef __section
 #define __section(x)        __attribute__((section(x)))
+#endif
+
+#ifndef __packed
 #define __packed            __attribute__((packed))
-#define __alias(x)          __attribute__((alias(x)))
+#endif
 
 #endif /* _KERN_MACROS_H */