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Date:   Thu, 10 Feb 2022 10:27:47 -0800
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Subject: Re: [PATCH] ACPI/IORT: Fix GCC 12 warning
Content-Language: en-US
To:     Robin Murphy <robin.murphy@arm.com>, lorenzo.pieralisi@arm.com
Cc:     guohanjun@huawei.com, sudeep.holla@arm.com, rafael@kernel.org,
        lenb@kernel.org, linux-acpi@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        trivial@kernel.org
References: <1644453141-1181-1-git-send-email-victor.erminpour@oracle.com>
 <fcb52c7b-a222-126e-fb3c-d57011506cf8@arm.com>
From:   Victor Erminpour <victor.erminpour@oracle.com>
In-Reply-To: <fcb52c7b-a222-126e-fb3c-d57011506cf8@arm.com>
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On 2/10/22 10:06 AM, Robin Murphy wrote:
> On 2022-02-10 00:32, Victor Erminpour 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;
>> | ^~~~~
>
> Notwithstanding the fact that that warning is nonsensical, this patch 
> changes valid C code into invalid C code that doesn't even compile:
>
> drivers/acpi/arm64/iort.c: In function 
> ‘acpi_iort_dma_get_max_cpu_address’:
> drivers/acpi/arm64/iort.c:1669:4: error: a label can only be part of a 
> statement and a declaration is not a statement
>  1669 |    struct acpi_iort_named_component *ncomp;
>       |    ^~~~~~
> drivers/acpi/arm64/iort.c:1676:4: error: a label can only be part of a 
> statement and a declaration is not a statement
>  1676 |    struct acpi_iort_root_complex *rc;
>       |    ^~~~~~
>
> Robin.
>

Hi Robin,

Thank you for your constructive criticism.
Could the solution be enclosing the case statement in curly braces?

I know this isn't a big issue for you, but this is a legitimate error 
for people
building the kernel with GCC 12 and CONFIG_INIT_STACK_ALL_ZERO enabled.

Regards,
--Victor


>> Signed-off-by: Victor Erminpour <victor.erminpour@oracle.com>
>> ---
>>   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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>