Re: [ARM] Add endless loop to avoid a compiler warning on noreturn functions.

["Richard Earnshaw (lists)" <Richard dot Earnshaw at arm dot com>]

On 02/10/18 07:52, Christophe Lyon wrote:
> On Tue, 2 Oct 2018 at 00:25, Craig Howland <howland@lgsinnovations.com> wrote:
>>
>> On 10/01/2018 05:27 PM, Christophe Lyon wrote:
>>> Hi,
>>>
>>> While building newlib for ARM, I noticed GCC warnings for _exit() that
>>> the compiler thinks they return a value despite being noreturn.
>>>
>>> Like other targets, this small adds an endless loop to avoid the warning.
>>>
>>> OK?
>>>
>>> Christophe
>> The proper fix (for both places) is to add noreturn to the _kill() prototype in
>> the file.  (Which presumably is true, otherwise _exit() will return.  I did test
>> that it fixes the warning.)  (It would not be surprising if it also needed to be
>> added to the _kill() source, itself.)
> 
> Well, when compiled with ARM_RDI_MONITOR, _kill does seem to return:
> #if SEMIHOST_V2
> if (_has_ext_exit_extended ())
>   return do_AngelSWI (insn, block);
> else
> #endif
>   return do_AngelSWI (insn, (void*)block[0]);
> 

do_AngelSWI is a multi-purpose call that will normally return, so that
can't be marked no-return.

I think the right fix here is to remove the "return" from the statements
and add __builtin_unreachable () at the end of the function.

R.

> I guess the noreturn should not be added to
> newlib/libc/include/sys/signal.h
> because it depends on the actual target implementation of _kill?
> 
>> Craig