[XEN PATCH][for-4.19 1/9] xen/include: add macro LOWEST_POW2

[Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>]

The purpose of this macro is to encapsulate the well-known expression
'x & -x', that in 2's complement architectures on unsigned integers will
give 2^ffs(x), where ffs(x) is the position of the lowest set bit in x.

A deviation for ECLAIR is also introduced.

Signed-off-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
---
 automation/eclair_analysis/ECLAIR/deviations.ecl | 6 ++++++
 xen/include/xen/macros.h                         | 6 ++++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/automation/eclair_analysis/ECLAIR/deviations.ecl 
b/automation/eclair_analysis/ECLAIR/deviations.ecl
index d8170106b449..016164643105 100644
--- a/automation/eclair_analysis/ECLAIR/deviations.ecl
+++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
@@ -274,6 +274,12 @@ still non-negative."
 -config=MC3R1.R10.1,etypes+={safe, 
"stmt(operator(logical)||node(conditional_operator||binary_conditional_operator))",
 "dst_type(ebool||boolean)"}
 -doc_end
 
+-doc_begin="The macro LOWEST_POW2 encapsulates a well-known pattern to obtain 
the value
+2^ffs(x) for unsigned integers on two's complement architectures
+(all the architectures supported by Xen satisfy this requirement)."
+-config=MC3R1.R10.1,reports+={safe, 
"any_area(any_loc(any_exp(macro(^LOWEST_POW2$))))"}
+-doc_end
+
 ### Set 3 ###
 
 #
diff --git a/xen/include/xen/macros.h b/xen/include/xen/macros.h
index d0caae7db298..bb9a1c9a53d0 100644
--- a/xen/include/xen/macros.h
+++ b/xen/include/xen/macros.h
@@ -8,8 +8,10 @@
 #define DIV_ROUND(n, d) (((n) + (d) / 2) / (d))
 #define DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
 
-#define MASK_EXTR(v, m) (((v) & (m)) / ((m) & -(m)))
-#define MASK_INSR(v, m) (((v) * ((m) & -(m))) & (m))
+#define LOWEST_POW2(x) ((x) & -(x))
+
+#define MASK_EXTR(v, m) (((v) & (m)) / LOWEST_POW2(m))
+#define MASK_INSR(v, m) (((v) * LOWEST_POW2(m)) & (m))
 
 #define count_args_(dot, a1, a2, a3, a4, a5, a6, a7, a8, x, ...) x
 #define count_args(args...) \
-- 
2.34.1