misra: deviate MISRA C Rule 10.1 for boolean operands of arithmetic
PATCH v2 1/1 misra: deviate MISRA C Rule 10.1 for boolean operands of arithmetic
MISRA C Rule 10.1 states: "Operands shall not be of an inappropriate essential type".
The result of relational, equality and logical negation operators has type int and value 0 or 1 (C99 6.5.8p6, 6.5.9p3, 6.5.3.3p5). An object or function result of type bool has value 0 or 1 too, and it is promoted to int (C99 6.3.1.2, 6.3.1.1p2). Using that value as an operand of binary +, -, *, <<, >>, <, >, <=, >= and of +=, -=, *=, <<=, >>= is well-defined. Division, remainder, unary plus and minus, and the increment operators stay covered by the rule. Update the ECLAIR configuration to tag the accepted uses as safe.
Update docs/misra/deviations.rst and rules.rst accordingly.
---
Test CI pipeline:
https://gitlab.com/xen-project/people/dimaprkp4k/xen/-/pipelines/3048651323
Changes in v2:
- use the same operator list in the ECLAIR config, deviations.rst and rules.rst
- extend deviation to: +, -, *, +=, -=, *=, <<, >>, <<=, >>=, <, >, <=, >=
- leave the full explanation in deviations.rst, ECLAIR config doc only names the operators and points there
--- .../eclair_analysis/ECLAIR/deviations.ecl | 4 ++++ docs/misra/deviations.rst | 20 +++++++++++++++++++ docs/misra/rules.rst | 4 ++++ 3 files changed, 28 insertions(+)
automation/eclair_analysis/ECLAIR/deviations.ecl +4 -0
@@ -335,6 +335,10 @@ still non-negative." -config=MC3A2.R10.1,etypes+={safe, "stmt(operator(logical)||node(conditional_operator||binary_conditional_operator))", "dst_type(ebool||boolean)"} -doc_end +-doc_begin="A 0-or-1 Boolean operand of binary +, -, *, <<, >>, <, >, <=, >= and of +=, -=, *=, <<=, >>= is safe. See docs/misra/deviations.rst for the full explanation." +-config=MC3A2.R10.1,etypes+={safe, "stmt(operator(add||sub||add_assign||sub_assign||mul||mul_assign||shl||shr||shl_assign||shr_assign||lt||gt||le||ge))", "src_type(ebool||boolean)"} +-doc_end + -doc_begin="The macro ISOLATE_LSB encapsulates a well-known pattern to obtain a mask where only the lowest bit set in the argument is set, if any, for unsigned integers arguments on two's complement architectures
docs/misra/deviations.rst +20 -0
@@ -347,6 +347,26 @@ Deviations related to MISRA C:2012 Rules: well-known to all Xen developers to be a comparison with 0. - Tagged as `safe` for ECLAIR. + * - R10.1 + - The result of relational, equality and logical negation operators has + type int and value 0 or 1 (C99 6.5.8p6, 6.5.9p3, 6.5.3.3p5). An object + or function result of type bool has value 0 or 1 too, and it is + promoted to int (C99 6.3.1.2, 6.3.1.1p2). Such a value is a + well-defined operand of the following operators. These are the operators + for which that 0-or-1 operand has a clear meaning. Binary + and - + (and += and -=) count something if the condition holds. \* (and \*=) + yields the other operand if the condition holds and 0 otherwise. + << and >> (and <<= and >>=) extend that selection to a shift: a Boolean + left operand contributes 0 or 1, and a Boolean right operand is a shift + count of 0 or 1. The operators <, >, <= and >= compare the same 0-or-1 + value, so false compares less than true. / and % (and /= and %=) are + excluded. A Boolean divisor is 0 when the condition is false, and + division or remainder by zero is undefined behavior (C99 6.5.5p5). + Unary plus, unary minus, increment and decrement are excluded too: + unary minus yields 0 or -1, and none of these is one of the meanings + above, so the rule still applies to them. + - Tagged as `safe` for ECLAIR. + * - R10.1 - Xen only supports architectures where signed integers are representend using two's complement and all the Xen developers are aware of this. For
docs/misra/rules.rst +4 -0
@@ -387,6 +387,10 @@ maintainers if you want to suggest a change. compilers' extensions) - Implicit conversions to boolean for conditionals (?: if while for) and logical operators (! || &&) + - Operands of essentially Boolean type (results of relational, + equality and logical negation operators, objects and function + results of type bool) used only with binary +, -, \*, <<, >>, + <, >, <=, >=, +=, -=, \*=, <<= and >>= - The essential type model allows the constants defined by anonymous enums (e.g., enum { A, B, C }) to be used as operands to arithmetic operators, as they have a signed essential type.
Signature · 1 line
2.43.0
Quoted 9 lines · On 10.11.2026 10:25, Dmytro Prokopchuk1 wrote:
MISRA C Rule 10.1 states: "Operands shall not be of an inappropriate essential type".
The result of relational, equality and logical negation operators has type int and value 0 or 1 (C99 6.5.8p6, 6.5.9p3, 6.5.3.3p5). An object or function result of type bool has value 0 or 1 too, and it is promoted to int (C99 6.3.1.2, 6.3.1.1p2). Using that value as an operand of binary +, -, *, <<, >>, <, >, <=, >= and of +=, -=, *=, <<=, >>= is well-defined. Division, remainder, unary plus and minus,
We did discuss division and remainder. What's wrong with unary plus and minus? Unary minus in particular can be used to create a mask value from a boolean (all bits set or all bits clear). And why would unary plus and minus be excluded when bitwise complement (which is less useful with a boolean operand than unary minus) is not?
As to relational operators (which it looks like we didn't discuss in v1):
Is it possible to express anything with them which cannot be expressed with equality operators? If not, I'd suggest keeping them out as well.
automation/eclair_analysis/ECLAIR/deviations.ecl still non-negative." · line 339
Quoted 8 lines
automation/eclair_analysis/ECLAIR/deviations.ecl +2
-0@@ -335,6 +335,10 @@ still non-negative." -config=MC3A2.R10.1,etypes+={safe, "stmt(operator(logical)||node(conditional_operator||binary_conditional_operator))", "dst_type(ebool||boolean)"} -doc_end +-doc_begin="A 0-or-1 Boolean operand of binary +, -, *, <<, >>, <, >, <=, >= and of +=, -=, *=, <<=, >>= is safe. See docs/misra/deviations.rst for the full explanation." +-config=MC3A2.R10.1,etypes+={safe, "stmt(operator(add||sub||add_assign||sub_assign||mul||mul_assign||shl||shr||shl_assign||shr_assign||lt||gt||le||ge))", "src_type(ebool||boolean)"}
Imo this wants shortening by making use of regex-es (provided such can be used here).
Jan