Re: [XEN PATCH] x86/uaccess: add attribute noreturn to __{get,put}_user_bad()

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.02.2024 14:35, Federico Serafini wrote:
> __get_user_bad() and __put_user_bad() are undefined symbols used
> to assert the unreachability of a program point:
> a call to one of such functions is optimized away if it is considered
> unreachable by the compiler. Otherwise, a linker error is reported.
> 
> In accordance with the purpose of such constructs:
> 1) add the attribute noreturn to __get_user_bad() and __put_user_bad();
> 2) change return type of __get_user_bad() to void (returning long is a
>    leftover from the past).
> 
> Point (1) meets the requirements to deviate MISRA C:2012 Rule 16.3
> ("An unconditional break statement shall terminate every switch
> clause") since functions with noreturn attribute are considered
> as allowed terminals for switch clauses.
> 
> Point (2) addresses several violations of MISRA C:2012 Rule 17.7
> ("The value returned by a function having non-void return type
> shall be used").
> 
> No functional change.
> 
> Signed-off-by: Federico Serafini <federico.serafini@xxxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
preferably ...

> --- a/xen/arch/x86/include/asm/uaccess.h
> +++ b/xen/arch/x86/include/asm/uaccess.h
> @@ -21,8 +21,8 @@ unsigned int copy_from_guest_ll(void *to, const void __user 
> *from, unsigned int
>  unsigned int copy_to_unsafe_ll(void *to, const void *from, unsigned int n);
>  unsigned int copy_from_unsafe_ll(void *to, const void *from, unsigned int n);
>  
> -extern long __get_user_bad(void);
> -extern void __put_user_bad(void);
> +extern void noreturn __get_user_bad(void);
> +extern void noreturn __put_user_bad(void);

... with the "extern" dropped at the same time (see other function
decls in context). I'll try to remember to drop them while committing.

Jan