[PATCH 1/7] xen/bitops: Cleanup ahead of rearrangements

[Andrew Cooper <andrew.cooper3@citrix.com>]

 * Rename __attribute_pure__ to just __pure before it gains users.
 * Identify the areas of xen/bitops.h which are a mess.
 * Create common/bitops.c for compile and runtime testing.  This provides a
   statement of the ABI, and a confirmation that arch-specific implementations
   behave as expected.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Wei Liu <wl@xen.org>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Julien Grall <julien@xen.org>
CC: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
CC: Bertrand Marquis <bertrand.marquis@arm.com>
CC: Michal Orzel <michal.orzel@amd.com>
CC: Oleksii Kurochko <oleksii.kurochko@gmail.com>
CC: Shawn Anastasio <sanastasio@raptorengineering.com>
CC: consulting@bugseng.com <consulting@bugseng.com>
CC: Simone Ballarin <simone.ballarin@bugseng.com>
CC: Federico Serafini <federico.serafini@bugseng.com>
CC: Nicola Vetrini <nicola.vetrini@bugseng.com>

I expect MISRA will have something to say about the macros here, but they are
in aid of better testing.
---
 xen/common/Makefile        |  1 +
 xen/common/bitops.c        | 41 ++++++++++++++++++++++++++++++++++++++
 xen/include/xen/bitops.h   | 13 +++++++++---
 xen/include/xen/compiler.h |  3 ++-
 4 files changed, 54 insertions(+), 4 deletions(-)
 create mode 100644 xen/common/bitops.c

diff --git a/xen/common/Makefile b/xen/common/Makefile
index e5eee19a8537..1f8ca9a2f4f8 100644
--- a/xen/common/Makefile
+++ b/xen/common/Makefile
@@ -1,5 +1,6 @@
 obj-$(CONFIG_ARGO) += argo.o
 obj-y += bitmap.o
+obj-y += bitops.o
 obj-$(CONFIG_GENERIC_BUG_FRAME) += bug.o
 obj-$(CONFIG_HYPFS_CONFIG) += config_data.o
 obj-$(CONFIG_CORE_PARKING) += core_parking.o
diff --git a/xen/common/bitops.c b/xen/common/bitops.c
new file mode 100644
index 000000000000..4c07191b4030
--- /dev/null
+++ b/xen/common/bitops.c
@@ -0,0 +1,41 @@
+#include <xen/bitops.h>
+#include <xen/bug.h>
+#include <xen/init.h>
+
+/* Hide a value from the optimiser. */
+#define HIDE(x) ({ typeof(x) _x = x; asm volatile ( "" : "+r" (_x) ); _x; })
+
+/*
+ * Check that fn(val) can be calcuated by the compiler, and that it gives the
+ * expected answer.
+ */
+#define COMPILE_CHECK(fn, val, res)                                     \
+    do {                                                                \
+        if ( fn(val) != res )                                           \
+            asm (".error \"Compile time check '" STR(fn(val) == res) "' failed\""); \
+    } while ( 0 )
+
+/*
+ * Check that Xen's runtime logic for fn(val) gives the expected answer.  This
+ * requires using HIDE() to prevent the optimiser from emitting the full
+ * calculation.
+ */
+#define RUNTIME_CHECK(fn, val, res)             \
+    do {                                        \
+        BUG_ON(fn(HIDE(val)) != res);           \
+    } while ( 0 )
+
+/*
+ * Perform compiletime and runtime checks for fn(val) == res.
+ */
+#define CHECK(fn, val, res)                     \
+    do {                                        \
+        COMPILE_CHECK(fn, val, res);            \
+        RUNTIME_CHECK(fn, val, res);            \
+    } while ( 0 )
+
+static int __init cf_check test_bitops(void)
+{
+    return 0;
+}
+__initcall(test_bitops);
diff --git a/xen/include/xen/bitops.h b/xen/include/xen/bitops.h
index e3c5a4ccf321..9b40f20381a2 100644
--- a/xen/include/xen/bitops.h
+++ b/xen/include/xen/bitops.h
@@ -1,5 +1,7 @@
-#ifndef _LINUX_BITOPS_H
-#define _LINUX_BITOPS_H
+#ifndef XEN_BITOPS_H
+#define XEN_BITOPS_H
+
+#include <xen/compiler.h>
 #include <xen/types.h>
 
 /*
@@ -103,8 +105,13 @@ static inline int generic_flsl(unsigned long x)
  * Include this here because some architectures need generic_ffs/fls in
  * scope
  */
+
+/* --------------------- Please tidy above here --------------------- */
+
 #include <asm/bitops.h>
 
+/* --------------------- Please tidy below here --------------------- */
+
 #ifndef find_next_bit
 /**
  * find_next_bit - find the next set bit in a memory region
@@ -294,4 +301,4 @@ static inline __u32 ror32(__u32 word, unsigned int shift)
 
 #define BIT_WORD(nr) ((nr) / BITS_PER_LONG)
 
-#endif
+#endif /* XEN_BITOPS_H */
diff --git a/xen/include/xen/compiler.h b/xen/include/xen/compiler.h
index 16d554f2a593..972719df55b3 100644
--- a/xen/include/xen/compiler.h
+++ b/xen/include/xen/compiler.h
@@ -85,7 +85,8 @@
 #define inline inline __init
 #endif
 
-#define __attribute_pure__  __attribute__((__pure__))
+#define __pure  __attribute__((__pure__))
+
 #define __attribute_const__ __attribute__((__const__))
 #define __transparent__     __attribute__((__transparent_union__))
 
-- 
2.30.2