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

[Victor Erminpour]

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@xxxxxxxxxx>
> > ---
> >   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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