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

Commit Message

Volodymyr Babchuk March 28, 2025, 12:19 p.m. UTC

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 <[e-mail]>

---

Changes in v2:

 - Use do { } while loop instead of initializing desc with NULL
---
 xen/arch/x86/irq.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

Comments

Jan Beulich March 28, 2025, 1:04 p.m. UTC | #1

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 <[e-mail]>
> 
> ---
> 
> 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

Patch

diff --git a/xen/arch/x86/irq.c b/xen/arch/x86/irq.c
index dd8d921f18..3224ada846 100644
--- 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
     {
         desc = irq_to_desc(irq);
         if (cmpxchg(&desc->arch.used, IRQ_UNUSED, IRQ_RESERVED) == IRQ_UNUSED)
            break;
-    }
+    } while ( ++irq < nr_irqs );
 
     if (irq >= nr_irqs)
          return -ENOSPC;