Hi Nicola,
On 12/10/2023 16:28, Nicola Vetrini wrote:
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.
In the commit message it is clear that the macro will return the lowest
set bit. But...
A deviation for ECLAIR is also introduced.
Signed-off-by: Nicola Vetrini <nicola.vetr...@bugseng.com>
---
Changes in v2:
- rename to LOWEST_BIT
---
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..b8e1155ee49d 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_BIT 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_BIT$))))"}
+-doc_end
+
### Set 3 ###
#
diff --git a/xen/include/xen/macros.h b/xen/include/xen/macros.h
index d0caae7db298..af47179d1056 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_BIT(x) ((x) & -(x))
... this is not reflected in the name of the macro. So it is not obvious
if it will return the lowest bit set or clear.
Can you at least add a comment on top explaining what it returns?
Something like:
/* Return the lowest bit set */
Cheers,
--
Julien Grall
