Re: [PATCH v2 2/3] xen: x86: irq: use do-while loop in create_irq()

[Jan Beulich <jbeulich@xxxxxxxx>]

On 28.03.2025 13:19, Volodymyr Babchuk wrote:
> While building xen with GCC 14.2.1 with "-fcondition-coverage" option,
> the compiler produces a false positive warning:
> 
>   arch/x86/irq.c: In function ‘create_irq’:
>   arch/x86/irq.c:281:11: error: ‘desc’ may be used uninitialized 
> [-Werror=maybe-uninitialized]
>     281 |     ret = init_one_irq_desc(desc);
>         |           ^~~~~~~~~~~~~~~~~~~~~~~
>   arch/x86/irq.c:269:22: note: ‘desc’ was declared here
>     269 |     struct irq_desc *desc;
>         |                      ^~~~
>   cc1: all warnings being treated as errors
>   make[2]: *** [Rules.mk:252: arch/x86/irq.o] Error 1
> 
> The same behavior can be observed when building Xen with "-Og"
> optimization level. Fix this by using "do { } while" loop instead of
> "for" loop.
> 
> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
> 
> ---
> 
> Changes in v2:
> 
>  - Use do { } while loop instead of initializing desc with NULL
> ---

I'm afraid to disappoint you by saying that I liked v1 better; all it was
lacking was a comment. Such a comment is still lacking here. Without that,
someone may come and convert this back to the more normal (in this
situation) "for" loop.

> --- a/xen/arch/x86/irq.c
> +++ b/xen/arch/x86/irq.c
> @@ -264,15 +264,19 @@ void __init clear_irq_vector(int irq)
>  
>  int create_irq(nodeid_t node, bool grant_access)
>  {
> -    int irq, ret;
> +    int ret;
> +    int irq = nr_irqs_gsi;
>      struct irq_desc *desc;
>  
> -    for (irq = nr_irqs_gsi; irq < nr_irqs; irq++)
> +    if ( irq >= nr_irqs )
> +        return -ENOSPC;
> +
> +    do
>      {

Nit: The brace goes on the same line as the "do", just like ...

>          desc = irq_to_desc(irq);
>          if (cmpxchg(&desc->arch.used, IRQ_UNUSED, IRQ_RESERVED) == 
> IRQ_UNUSED)
>             break;
> -    }
> +    } while ( ++irq < nr_irqs );

... it's on the same line as the "while" here.

Jan