On 30.07.2025 16:06, Dmytro Prokopchuk1 wrote:
> From: Nicola Vetrini <nicola.vetr...@bugseng.com>
>
> MISRA C Rule 2.1 states: "A project shall not contain unreachable code".
> Functions that are non-returning and are not explicitly annotated with
> the `noreturn' attribute are considered a violation of this rule.
>
> In certain cases, some functions might be non-returning in debug build
> configuration (when `NDEBUG' is not defined), due to calls to
> `__builtin_unreachable' in the expansion of the macro `ASSERT_UNREACHABLE()'.
>
> Conversely, in non-debug (release) builds (when `NDEBUG' is defined),
> the macro `ASSERT_UNREACHABLE()' expands to an empty construct
> (`do { } while (0)'), which does not affect the execution flow.
> This allows such functions to return normally in release builds,
> avoiding unreachable code.
While this way of putting it is technically correct as long as all we have
is
#ifndef CONFIG_DEBUG
#define NDEBUG
#endif
in xen/config.h, but I think it would be better if "debug builds"
(controlled by CONFIG_DEBUG) were properly separated from assertions
being active (NDEBUG). For quite some time there has been the plan to
decouple the two.
Similarly, throughout: You write ASSERT_UNREACHABLE() (i.e. including
the parentheses), yet oddly you then don't similarly include them when
referring to __builtin_unreachable().
> --- a/docs/misra/rules.rst
> +++ b/docs/misra/rules.rst
> @@ -124,6 +124,15 @@ maintainers if you want to suggest a change.
> they are used to generate definitions for asm modules
> - Declarations without initializer are safe, as they are not
> executed
> + - Functions that are noreturn due to calls to `ASSERT_UNREACHABLE`
> + macro in debug build configurations are not reported as
> violations::
I find "reported" odd to appear in this file. My take is that here we
describe our intentions, not what some tool may be doing. I'd suggest
"deemed" as replacement.
Jan
> + static inline bool
> + arch_vcpu_ioreq_completion(enum vio_completion completion)
> + {
> + ASSERT_UNREACHABLE();
> + return false;
> + }
>
> * - `Rule 2.6
> <https://gitlab.com/MISRA/MISRA-C/MISRA-C-2012/Example-Suite/-/blob/master/R_02_06.c>`_
> - Advisory
