Re: [PATCH] bug.h: Work around GCC PR82365 in BUG()

[Arnd Bergmann]

On Tue, Dec 19, 2017 at 5:57 PM, Vineet Gupta
<Vineet.Gupta1@xxxxxxxxxxxx> wrote:
> On 12/19/2017 03:41 AM, Arnd Bergmann wrote:

>> In case of ARC and CRIS, it turns out that the BUG() implementation
>> actually does return (or at least the compiler thinks it does), resulting
>> in lots of warnings about uninitialized variable use and leaving noreturn
>> functions, such as:
>>
>> block/cfq-iosched.c: In function 'cfq_async_queue_prio':
>> block/cfq-iosched.c:3804:1: error: control reaches end of non-void
>> function [-Werror=return-type]
>> include/linux/dmaengine.h: In function 'dma_maxpq':
>> include/linux/dmaengine.h:1123:1: error: control reaches end of non-void
>> function [-Werror=return-type]

>> diff --git a/arch/arc/include/asm/bug.h b/arch/arc/include/asm/bug.h
>> index ea022d47896c..21ec82466d62 100644
>> --- a/arch/arc/include/asm/bug.h
>> +++ b/arch/arc/include/asm/bug.h
>> @@ -23,7 +23,8 @@ void die(const char *str, struct pt_regs *regs, unsigned
>> long address);
>>     #define BUG()       do {
>> \
>>         pr_warn("BUG: failure at %s:%d/%s()!\n", __FILE__, __LINE__,
>> __func__); \
>> -       dump_stack();
>> \
>> +       barrier_before_unreachable();
>> \
>> +       __builtin_trap();
>> \
>>   } while (0)
>>     #define HAVE_ARCH_BUG
>
>
> I suppose BUG() implies "dead end" like semantics - which ARC was lacking
> before ?

Correct. Using __builtin_trap() here avoids the 'control reaches end of non-void
function' warnings, but then makes us run into the stack size problem that
I work around with the barrier_before_unreachable().

It would be good if you could give this a quick test to see if you get sensible
output from the __builtin_trap();

         Arnd