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From:   Vineet Gupta <Vineet.Gupta1@synopsys.com>
To:     Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>,
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Subject: Re: [PATCH] ARC: ARCv2: jump label: implement jump label patching
Thread-Topic: [PATCH] ARC: ARCv2: jump label: implement jump label patching
Thread-Index: AQHVPLGkQUnMGryojE2rPVU+oeatwQ==
Date:   Wed, 17 Jul 2019 17:45:52 +0000
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On 7/17/19 8:09 AM, Eugeniy Paltsev wrote:=0A=
>>> +/* Halt system on fatal error to make debug easier */=0A=
>>> +#define arc_jl_fatal(format...)						\=0A=
>>> +({									\=0A=
>>> +	pr_err(JUMPLABEL_ERR format);					\=0A=
>>> +	BUG();								\=0A=
>> Does it make sense to bring down the whole system vs. failing and return=
ing.=0A=
>> I see there is no error propagation to core code, but still.=0A=
> I totally agree with Peter, and I prefer to stop the system on this error=
s. Here is few arguments:=0A=
> All this checks can't be toggle in system operating normally and only may=
 be caused by bad code generation (or some code/data corruption):=0A=
> 1) We got our instruction to patch unaligned by 4 bytes (despite the fact=
 that we used '.balign 4' to align it)=0A=
> 2) We got branch offset unaligned (which means that we calculate it wrong=
 at build time or corrupt it in run time)=0A=
> 3) We got branch offset which not fits into s25. As this is offset inside=
 one function (inside one 'if' statement actually) we newer get such huge=
=0A=
> offset in real life if code generation is ok.=0A=
=0A=
I understand that. But AFAIKR in implementation arc_jl_fatal() gets called =
before=0A=
we have done the actual code patching and/or flushing the caches to that ef=
fect.=0A=
So harm has been done just yet. We just need to make sure that any book-kee=
ping of=0A=
true/false is not yet done or unrolled.=0A=
=0A=
> If we only warn to log and return we will face with compromised kernel fl=
ow later.=0A=
> I.E. it could be 'if' statement in kernel text which is switched to wrong=
 state: the condition is true but we take the false branch.=0A=
> And It will be the issue which is much more difficult to debug.=0A=
>=0A=
> Does it sound reasonably?=0A=
=0A=
I'm still not convinced that by hitting the _fatal() we are in some inconsi=
stent=0A=
state already. But if u feel strongly lets keep it.=0A=
=0A=
>=0A=
> If you really don't want to have BUG here, I can make it conditionally en=
abled=0A=
=0A=
Not a good idea. It is unconditionally present or not. Not something in bet=
ween.=0A=
=0A=
> in depend on CONFIG_ARC_STATIC_KEYS_DEBUG as I want to have it enabled at=
 least on ARC development platforms.=0A=
=0A=
=0A=