From: Bernd Edlinger <bernd.edlinger@hotmail.de>
To: Christophe Lyon <christophe.lyon@linaro.org>,
Dimitar Dimitrov <dimitar@dinux.eu>,
Segher Boessenkool <segher@kernel.crashing.org>,
"Thomas Preudhomme" <thomas.preudhomme@linaro.org>,
"gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>,
"richard.sandiford@arm.com" <richard.sandiford@arm.com>
Subject: Re: [PATCH] [RFC] PR target/52813 and target/11807
Date: Mon, 17 Dec 2018 14:10:00 -0000 [thread overview]
Message-ID: <DB7PR07MB53534C8D97E7CB29B687A641E4BC0@DB7PR07MB5353.eurprd07.prod.outlook.com> (raw)
In-Reply-To: <87lg4o46oj.fsf@arm.com>
On 12/17/18 2:35 PM, Richard Sandiford wrote:
> Christophe Lyon <christophe.lyon@linaro.org> writes:
>> On Mon, 17 Dec 2018 at 12:47, Richard Sandiford
>> <richard.sandiford@arm.com> wrote:
>>>
>>> Dimitar Dimitrov <dimitar@dinux.eu> writes:
>>>> On Sun, Dec 16 2018 at 14:36:26 EET Bernd Edlinger wrote:
>>>>> Hi,
>>>>>
>>>>> if I understood that right, then clobbering sp is and has always been
>>>>> ignored.
>>>
>>> PR77904 was about the clobber not being ignored, so the behaviour
>>> hasn't been consistent.
>>>
>>> I'm also not sure it was always ignored in recent sources. The clobber
>>> does get added to the associated rtl insn, and it'd be surprising if
>>> that never had an effect.
>>>
>>>>> If that is right, then I would much prefer a warning, that says exactly
>>>>> that, because that would also help to understand why removing that clobber
>>>>> statement is safe even for old gcc versions.
>>>
>>> If the asm does leave sp with a different value, then it's never been safe,
>>> regardless of the gcc version. That's why an error seems more appropriate.
>>>
>>>> Thank you. Looks like general consensus is to have a warning. See attached
>>>> patch that switches the error to a warning.
>>>
>>> I don't think there's a good reason to treat this differently from the
>>> preexisting PIC register error. If the argument for making it a warning
>>> rather than an error is that the asm might happen to work by accident,
>>> then the same is true for the PIC register.
>>>
>>
>> If we leave the error, maybe a more explanatory message would be helpful?
>> (along the lines of what I posted earlier in this thread, which may be
>> too verbose)
>
> The message in that patch suggested removing the clobber and hoping for
> the best, which IMO is bad advice. If the current message doesn't make
> it clear enough that changing the sp is not allowed, how about:
>
> inline %<asm%> statements must not change the value of the stack pointer
>
> ?
>
Yes, things could be easy, but, mot the closer one looks, the more complicated
they get...
Even pushing a value on the stack and popping it again in the _same_ asm statement
is dangerous with red-zone targets. Maybe that would be also good to add as an advice?
Bernd.
> Thanks,
> Richard
>
>
>
next prev parent reply other threads:[~2018-12-17 14:10 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-16 14:36 Bernd Edlinger
2018-12-16 16:14 ` Dimitar Dimitrov
2018-12-17 11:47 ` Richard Sandiford
2018-12-17 12:54 ` Christophe Lyon
2018-12-17 13:35 ` Richard Sandiford
2018-12-17 13:42 ` Christophe Lyon
2018-12-17 14:05 ` Bernd Edlinger
2018-12-17 14:10 ` Bernd Edlinger [this message]
2018-12-17 15:55 ` Segher Boessenkool
2018-12-17 18:46 ` Richard Sandiford
2018-12-17 20:15 ` Bernd Edlinger
2018-12-19 6:40 ` Dimitar Dimitrov
2018-12-19 9:29 ` Segher Boessenkool
2018-12-18 14:16 ` Bernd Edlinger
2018-12-18 15:14 ` Bernd Edlinger
2019-01-07 9:23 ` Jakub Jelinek
2019-01-07 21:51 ` Bernd Edlinger
2019-01-08 12:03 ` Richard Sandiford
2019-01-10 13:21 ` Segher Boessenkool
2019-01-10 21:23 ` Richard Sandiford
2019-01-10 21:26 ` Jakub Jelinek
2019-01-10 21:56 ` Richard Sandiford
2019-01-11 12:26 ` Segher Boessenkool
2019-01-10 22:32 ` Bernd Edlinger
2019-01-11 12:18 ` Segher Boessenkool
2019-01-11 12:23 ` Richard Sandiford
2019-01-11 22:59 ` Jeff Law
2019-01-17 14:27 ` Christophe Lyon
2019-01-18 9:49 ` Richard Sandiford
-- strict thread matches above, loose matches on Subject: below --
2018-12-09 10:09 Dimitar Dimitrov
2018-12-10 11:21 ` Richard Sandiford
2018-12-10 19:36 ` Dimitar Dimitrov
2018-12-11 15:52 ` Richard Sandiford
2018-12-12 9:42 ` Christophe Lyon
2018-12-12 10:03 ` Christophe Lyon
2018-12-12 16:39 ` Dimitar Dimitrov
2018-12-12 10:30 ` Thomas Preudhomme
2018-12-12 11:21 ` Thomas Preudhomme
2018-12-12 13:19 ` Christophe Lyon
2018-12-12 15:13 ` Christophe Lyon
2018-12-12 15:35 ` Thomas Preudhomme
2018-12-12 16:26 ` Dimitar Dimitrov
2018-12-13 14:49 ` Segher Boessenkool
2018-12-13 22:21 ` Dimitar Dimitrov
2018-12-14 8:52 ` Segher Boessenkool
2018-12-16 8:43 ` Dimitar Dimitrov
2018-12-17 15:23 ` Segher Boessenkool
2018-12-14 13:49 ` Richard Sandiford
2018-12-15 15:38 ` Segher Boessenkool
2018-12-12 11:24 ` Andreas Schwab
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