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From:   Ard Biesheuvel <ardb@kernel.org>
Date:   Thu, 10 Feb 2022 10:11:46 +0100
Message-ID: <CAMj1kXHUOJ-3CXFUJ9ULQuSoRh1=d3PJ15eFUsdGjQtUHozSpA@mail.gmail.com>
Subject: Re: [PATCH] ACPI/IORT: Fix GCC 12 warning
To:     Victor Erminpour <victor.erminpour@oracle.com>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Hanjun Guo <guohanjun@huawei.com>,
        Sudeep Holla <sudeep.holla@arm.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Len Brown <lenb@kernel.org>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        trivial@kernel.org
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On Thu, 10 Feb 2022 at 01:34, Victor Erminpour
<victor.erminpour@oracle.com> wrote:
>
> When building with automatic stack variable initialization, GCC 12
> complains about variables defined outside of switch case statements.
> Move the variable into the case that uses it, which silences the warning:
>
> ./drivers/acpi/arm64/iort.c:1670:59: error: statement will never be executed [-Werror=switch-unreachable]
>   1670 |                         struct acpi_iort_named_component *ncomp;
>        |                                                           ^~~~~
>
> Signed-off-by: Victor Erminpour <victor.erminpour@oracle.com>

GCC 12 is not released yet, and this is clearly a compiler bug (a
declaration is not a statement, and the hidden offending statement
[the zero-init] is emitted by the compiler itself), so please report
this to the GCC folks instead.


> ---
>  drivers/acpi/arm64/iort.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
> index 3b23fb775ac4..5c5d2e56d756 100644
> --- a/drivers/acpi/arm64/iort.c
> +++ b/drivers/acpi/arm64/iort.c
> @@ -1645,7 +1645,7 @@ void __init acpi_iort_init(void)
>   */
>  phys_addr_t __init acpi_iort_dma_get_max_cpu_address(void)
>  {
> -       phys_addr_t limit = PHYS_ADDR_MAX;
> +       phys_addr_t local_limit, limit = PHYS_ADDR_MAX;
>         struct acpi_iort_node *node, *end;
>         struct acpi_table_iort *iort;
>         acpi_status status;
> @@ -1667,17 +1667,15 @@ phys_addr_t __init acpi_iort_dma_get_max_cpu_address(void)
>                         break;
>
>                 switch (node->type) {
> -                       struct acpi_iort_named_component *ncomp;
> -                       struct acpi_iort_root_complex *rc;
> -                       phys_addr_t local_limit;
> -
>                 case ACPI_IORT_NODE_NAMED_COMPONENT:
> +                       struct acpi_iort_named_component *ncomp;
>                         ncomp = (struct acpi_iort_named_component *)node->node_data;
>                         local_limit = DMA_BIT_MASK(ncomp->memory_address_limit);
>                         limit = min_not_zero(limit, local_limit);
>                         break;
>
>                 case ACPI_IORT_NODE_PCI_ROOT_COMPLEX:
> +                       struct acpi_iort_root_complex *rc;
>                         if (node->revision < 1)
>                                 break;
>
>
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