[8u] RFR: JDK-8164041: support old pre-c++11 toolchains and ucLibc

[Alex Kashchenko]

Hi Andrey,

On 08/24/2016 06:25 PM, Andrey Petushkov wrote:
> Hi Alex,
>
> You, you're right and thank you for the fix! One small correction, I
> believe there should be "itttt" rather than "ittt" :)

I believe it is "ittt" (sorry, cannot check right now, currently on 
vacation), as I remember jvm hangs on startup with "itttt". But of 
course this is a very minor detail that will be immediately clear from 
thumb builds.

>
> I'll include this fix into second revision of the patch update in
> accordance with the results of discussion with Ed
>
> Regards,
> Andrey
>
> PS. Pardon for delay, was busy preparing the C1 monster, it did not come
> easy for some reason
>
> On Fri, Aug 19, 2016 at 9:51 AM Alex Kashchenko <akashche at redhat.com> wrote:
>
>> Hi,
>>
>> On 08/15/2016 07:06 PM, Andrey Petushkov wrote:
>>> Hi All,
>>>
>>> We met a necessity to support an older kind of gcc toolchain which does
>> not fully conform to c++ 11 and in particular do not have __atomic API as
>> well as have some other peculiarities. In addition the support of ucLibc
>> was desired.
>>>
>>> The resulting changes are here:
>> http://cr.openjdk.java.net/~apetushkov/8164041/webrev/ <
>> http://cr.openjdk.java.net/~apetushkov/8164041/webrev/>
>>> Checked with running on OpenWRT-based distribution
>>>
>>> When implementing the replacement code we also chosen to always use the
>> assembly implementation and not builtins because:
>>> - there is no harm, the assembly is no worse than that gcc can generate
>>> - the code is more clear
>>> - there is no reliable way to determine if gcc has flaws or not, so the
>> detection directives look really ugly
>>>
>>> Thanks,
>>> Andrey
>>>
>>
>> A small fix for thumb mode (that is default on ubuntu xenial): in
>> Atomic::cmpxchg add "ittt eq" before the "cmpeq". Otherwise it will fail
>> on thumb with:
>>
>> {standard input}: Assembler messages:
>> {standard input}:926: Error: thumb conditional instruction should be in
>> IT block -- `cmpeq r6,r2'
>> {standard input}:927: Error: thumb conditional instruction should be in
>> IT block -- `strexdeq lr,r3,r4,[r0]'
>> {standard input}:928: Error: thumb conditional instruction should be in
>> IT block -- `cmpeq lr,#1'
>> /home/u1604/jdk8u/hotspot/make/linux/makefiles/rules.make:157: recipe
>> for target 'atomic.o' failed
>>
>>
>> --
>> -Alex
>>
>


-- 
-Alex