Re: [PATCH] ACPI/IORT: Fix GCC 12 warning

[Victor Erminpour <victor.erminpour@oracle.com>]

On 2/10/22 1:11 AM, Ard Biesheuvel wrote:
> 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.

Hi Ard,

Thanks for the reply.
This fix is similar to the following commits that have been integrated 
upstream:
https://lore.kernel.org/linux-hardening/20211209043456.1377875-1-keescook@chromium.org/
https://lore.kernel.org/linux-hardening/20211209043915.1378393-1-keescook@chromium.org/

You're not obligated to integrate this commit, but you may run into this 
issue once
upstream starts using GCC 12 (or a patched version of GCC 11 in my case) 
with the
CONFIG_INIT_STACK_ALL_ZERO option enabled.

Regards,
--Victor


>
>> ---
>>   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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