* Rename __attribute_pure__ to just __pure before it gains users.
* Introduce __constructor which is going to be used in lib/, and is
unconditionally cf_check.
* Identify the areas of xen/bitops.h which are a mess.
* Introduce xen/boot-check.h as helpers for compile and boot time testing.
This provides a statement of the ABI, and a confirmation that arch-specific
implementations behave as expected.
Sadly Clang 7 and older isn't happy with the compile time checks. Skip them,
and just rely on the runtime checks.
Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
---
CC: Jan Beulich <jbeul...@suse.com>
CC: Roger Pau Monné <roger....@citrix.com>
CC: Wei Liu <w...@xen.org>
CC: Stefano Stabellini <sstabell...@kernel.org>
CC: Julien Grall <jul...@xen.org>
CC: Volodymyr Babchuk <volodymyr_babc...@epam.com>
CC: Bertrand Marquis <bertrand.marq...@arm.com>
CC: Michal Orzel <michal.or...@amd.com>
CC: Oleksii Kurochko <oleksii.kuroc...@gmail.com>
CC: Shawn Anastasio <sanasta...@raptorengineering.com>
CC: consult...@bugseng.com <consult...@bugseng.com>
CC: Simone Ballarin <simone.balla...@bugseng.com>
CC: Federico Serafini <federico.seraf...@bugseng.com>
CC: Nicola Vetrini <nicola.vetr...@bugseng.com>
v2:
* Break macros out into a header as they're going to be used elsewhere too
* Use panic() rather than BUG_ON() to be more helpful when something fails
* Brackets in HIDE()
* Alignment adjustments
* Skip COMPILE_CHECK() for Clang < 8
---
xen/include/xen/bitops.h | 13 ++++++--
xen/include/xen/boot-check.h | 60 ++++++++++++++++++++++++++++++++++++
xen/include/xen/compiler.h | 3 +-
3 files changed, 72 insertions(+), 4 deletions(-)
create mode 100644 xen/include/xen/boot-check.h
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/boot-check.h b/xen/include/xen/boot-check.h
new file mode 100644
index 000000000000..250f9a40d3b0
--- /dev/null
+++ b/xen/include/xen/boot-check.h
@@ -0,0 +1,60 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+/*
+ * Helpers for boot-time checks of basic logic, including confirming that
+ * examples which should be calculated by the compiler are.
+ */
+#ifndef XEN_BOOT_CHECK_H
+#define XEN_BOOT_CHECK_H
+
+#include <xen/lib.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.
+ *
+ * Clang < 8 can't fold constants through static inlines, causing this to
+ * fail. Simply skip it for incredibly old compilers.
+ */
+#if !CONFIG_CC_IS_CLANG || CONFIG_CLANG_VERSION >= 80000
+#define COMPILE_CHECK(fn, val, res) \
+ do { \
+ typeof(fn(val)) real = fn(val); \
+ \
+ if ( !__builtin_constant_p(real) ) \
+ asm ( ".error \"'" STR(fn(val)) "' not compile-time constant\"" );
\
+ else if ( real != res ) \
+ asm ( ".error \"Compile time check '" STR(fn(val) == res) "'
failed\"" ); \
+ } while ( 0 )
+#else
+#define COMPILE_CHECK(fn, val, res)
+#endif
+
+/*
+ * Check that Xen's runtime logic for fn(val) gives the expected answer. This
+ * requires using HIDE() to prevent the optimiser from collapsing the logic
+ * into a constant.
+ */
+#define RUNTIME_CHECK(fn, val, res) \
+ do { \
+ typeof(fn(val)) real = fn(HIDE(val)); \
+ \
+ if ( real != res ) \
+ panic("%s: %s(%s) expected %u, got %u\n", \
+ __func__, #fn, #val, real, 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 )
+
+#endif /* XEN_BOOT_CHECK_H */
diff --git a/xen/include/xen/compiler.h b/xen/include/xen/compiler.h
index 179ff23e62c5..444bf80142c7 100644
--- a/xen/include/xen/compiler.h
+++ b/xen/include/xen/compiler.h
@@ -86,7 +86,8 @@
#define inline inline __init
#endif
-#define __attribute_pure__ __attribute__((__pure__))
+#define __constructor __attribute__((__constructor__)) cf_check
+#define __pure __attribute__((__pure__))
#define __attribute_const__ __attribute__((__const__))
#define __transparent__ __attribute__((__transparent_union__))
--
2.30.2
