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SubjectRe: [PATCH] s390: add unreachable() to dump_fault_info() to fix -Wmaybe-uninitialized
On Fri, 17 May 2019 15:49:22 +0900
Masahiro Yamada <yamada.masahiro@socionext.com> wrote:

> When CONFIG_OPTIMIZE_INLINING is enabled for s390, I see this warning:
>
> arch/s390/mm/fault.c:127:15: warning: 'asce' may be used uninitialized in this function [-Wmaybe-uninitialized]
> switch (asce & _ASCE_TYPE_MASK) {
> arch/s390/mm/fault.c:177:16: note: 'asce' was declared here
> unsigned long asce;
> ^~~~
>
> If get_fault_type() is not inlined, the compiler cannot deduce that
> all the possible paths in the 'switch' statement are covered.
>
> Of course, we could mark get_fault_type() as __always_inline to get
> back the original behavior, but I do not think it sensible to force
> inlining just for the purpose of suppressing the warning. Since this
> is just a matter of warning, I want to keep as much room for compiler
> optimization as possible.
>
> I added unreachable() to teach the compiler that the 'default' label
> is unreachable.
>
> I got rid of the 'inline' marker. Even without the 'inline' hint,
> the compiler inlines functions based on its inlining heuristic.
>
> Fixes: 9012d011660e ("compiler: allow all arches to enable CONFIG_OPTIMIZE_INLINING")
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Added to our internal tree and I will add it to s390/linux soon. Thanks.

> ---
>
> arch/s390/mm/fault.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
> index c220399ae196..91ce03fd0c84 100644
> --- a/arch/s390/mm/fault.c
> +++ b/arch/s390/mm/fault.c
> @@ -85,7 +85,7 @@ static inline int notify_page_fault(struct pt_regs *regs)
> * Find out which address space caused the exception.
> * Access register mode is impossible, ignore space == 3.
> */
> -static inline enum fault_type get_fault_type(struct pt_regs *regs)
> +static enum fault_type get_fault_type(struct pt_regs *regs)
> {
> unsigned long trans_exc_code;
>
> @@ -211,6 +211,8 @@ static void dump_fault_info(struct pt_regs *regs)
> asce = S390_lowcore.kernel_asce;
> pr_cont("kernel ");
> break;
> + default:
> + unreachable();
> }
> pr_cont("ASCE.\n");
> dump_pagetable(asce, regs->int_parm_long & __FAIL_ADDR_MASK);


--
blue skies,
Martin.

"Reality continues to ruin my life." - Calvin.

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