Re: [PATCH] afs: fix no return statement in function returning non-void

[Randy Dunlap]

On 6/15/21 5:32 PM, Linus Torvalds wrote:
> On Tue, Jun 15, 2021 at 4:58 PM Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote:
>>
>> Some implementations of BUG() are macros, not functions,
> 
> Not "some", I think. Most.
> 
>> so "unreachable" is not applicable AFAIK.
> 
> Sure it is. One common pattern is the x86 one:
> 
>   #define BUG()                                                   \
>   do {                                                            \
>           instrumentation_begin();                                \
>           _BUG_FLAGS(ASM_UD2, 0);                                 \
>           unreachable();                                          \
>   } while (0)

duh.

> and that "unreachable()" is exactly what I'm talking about.
> 
> So I repeat: what completely broken compiler / config / architecture
> is it that needs that "return 0" after a BUG() statement?

I have seen it on ia64 -- most likely GCC 9.3.0, but I'll have to
double check that.

> Because that environment is broken, and the warning is bogus and wrong.
> 
> It might not be the compiler. It might be some architecture that does
> this wrong. It might be some very particular configuration that does
> something bad and makes the "unreachable()" not work (or not exist).
> 
> But *that* is the bug that should be fixed. Not adding a pointless and
> incorrect line that makes no sense, just to hide the real bug.