Re: [PATCH] softmmu/physmem: Hint notifier is not NULL in as_translate_for_iotlb()

[Peter Maydell]

On Sun, 17 Jan 2021 at 16:07, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>
> When using GCC 10.2 configured with --extra-cflags=-Os, we get:
>
>   softmmu/physmem.c: In function ‘address_space_translate_for_iotlb’:
>   softmmu/physmem.c:643:26: error: ‘notifier’ may be used uninitialized in 
> this function [-Werror=maybe-uninitialized]
>     643 |         notifier->active = true;
>         |                          ^
>   softmmu/physmem.c:608:23: note: ‘notifier’ was declared here
>     608 |     TCGIOMMUNotifier *notifier;
>         |                       ^~~~~~~~
>
> Insert assertions as hint to the compiler that 'notifier' can
> not be NULL there.
>
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
> Yet another hole in our CI.
> ---
>  softmmu/physmem.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/softmmu/physmem.c b/softmmu/physmem.c
> index 6301f4f0a5c..65602ed548e 100644
> --- a/softmmu/physmem.c
> +++ b/softmmu/physmem.c
> @@ -605,7 +605,7 @@ static void tcg_register_iommu_notifier(CPUState *cpu,
>       * when the IOMMU tells us the mappings we've cached have changed.
>       */
>      MemoryRegion *mr = MEMORY_REGION(iommu_mr);
> -    TCGIOMMUNotifier *notifier;
> +    TCGIOMMUNotifier *notifier = NULL;
>      int i;
>
>      for (i = 0; i < cpu->iommu_notifiers->len; i++) {
> @@ -638,6 +638,7 @@ static void tcg_register_iommu_notifier(CPUState *cpu,
>          memory_region_register_iommu_notifier(notifier->mr, &notifier->n,
>                                                &error_fatal);
>      }
> +    assert(notifier != NULL);
>
>      if (!notifier->active) {
>          notifier->active = true;

Is the assert() necessary to prevent the compiler complaining?
Usually we don't bother if it's about to be dereferenced anyway.

thanks
-- PMM