RFR : 8202322: AIX: symbol visibility flags not support on xlc 12.1

Thomas Stüfe thomas.stuefe at gmail.com
Fri Apr 27 15:58:53 UTC 2018


On Fri, Apr 27, 2018 at 5:01 PM, Baesken, Matthias
<matthias.baesken at sap.com> wrote:
>> I see tons of exports listed, most of which do not have the static
>> keyword. So, I would expect them to be exported from their compilation
>> unit, but not from the linked shared library? Am I making a thinking
>> error here?
>
> Hi Thomas , I see  "a ton"  of exported symbols as well  when looking into it (e.g. libjvm.so)  with dump .
> More than one would like to have .
>

Okay, thanks for confirming this! I was not sure if I was using nm
correctly, or if it was lying to me.

> However  for now I think we  should progress with the suggested patch as it is.
>

I agree, patch is fine. Thanks for fixing this.

> Once we switch to xlc 13  (or some follow up release of xlc)  that  supports  the visibility attributes
> ( as decribed in   https://www.ibm.com/developerworks/aix/library/au-aix-symbol-visibility/index.html  )
>  we can open a follow up item  with compiler flag adjustment and  adjust     src/java.base/unix/native/include/jni_md.h     , I think this file misses  a proper  JNIEXPORT definition for AIX / xlc 13.1  ).
>

Okay, fine with me.

Best Regards, Thomas

>
> Best regards, Matthias
>
>
>
>> -----Original Message-----
>> From: Thomas Stüfe [mailto:thomas.stuefe at gmail.com]
>> Sent: Freitag, 27. April 2018 10:04
>> To: Langer, Christoph <christoph.langer at sap.com>
>> Cc: Volker Simonis <volker.simonis at gmail.com>; Baesken, Matthias
>> <matthias.baesken at sap.com>; Simonis, Volker <volker.simonis at sap.com>;
>> ppc-aix-port-dev at openjdk.java.net; core-libs-dev at openjdk.java.net; build-
>> dev at openjdk.java.net
>> Subject: Re: RFR : 8202322: AIX: symbol visibility flags not support on xlc 12.1
>>
>> On Fri, Apr 27, 2018 at 9:27 AM, Langer, Christoph
>> <christoph.langer at sap.com> wrote:
>> > Hi Thomas,
>> >
>> > let me cite one section from the article:
>> >
>> > ----------------------------------------------
>> >
>> > Visibility attribute and backward compatibility on AIX
>> >
>> > As we know from the previous article, on AIX, symbols are not visible by
>> default unless we export them at the linking stage, either manually or with
>> the help of CreateExportList. However, on Linux, symbols are, by default,
>> with export (namely default) visibility. This brings a gap between the AIX
>> visibility attribute and the GNU visibility attribute. To be backward
>> compatible, on AIX, XL C/C++ would not set all the symbols to be exported
>> like Linux. It might consider symbol without any visibility setting to be an
>> unspecific visibility, which aligns with an old AIX implementation. For such
>> symbols, AIX compiler, linker, and related tools would handle it as before.
>> However, unspecific visibility does not mean that the symbol is internal or
>> invisible at all. It is just a visibility that is specially designed to keep the
>> compatibility.
>> >
>> > ...
>> >
>> > ----------------------------------------------
>> >
>> > It says in the first sentence: " As we know from the previous article, on AIX,
>> symbols are not visible by default unless we export them at the linking stage,
>> either manually or with the help of CreateExportList". I guess that is why I
>> was under the impression that with xlc12 symbols would not be visible...
>> >
>>
>> :) Thanks for that pointer.
>>
>> I did read:
>>
>> "Consequently, as we have mentioned at the beginning of this article,
>> if the programmer does not explicitly specify the visibility attribute
>> for a symbol, on Linux, the visibility of the symbol could be
>> thedefault. But on AIX, the visibility would be unspecified."
>>
>> So I thought, default is "unspecified", which is not hidden.
>>
>> I just had a look at the libjvm.so from our nightly fastdebug build,
>> using "nm -g".
>>
>> I see tons of exports listed, most of which do not have the static
>> keyword. So, I would expect them to be exported from their compilation
>> unit, but not from the linked shared library? Am I making a thinking
>> error here?
>>
>> Anyway. I do not want to hold up this patch if you guys think it is
>> okay to ignore the compiler warning, so it is okay by me.
>>
>> Best Regards, Thomas
>>
>>
>> > Best regards
>> > Christoph
>> >
>> >> -----Original Message-----
>> >> From: Thomas Stüfe [mailto:thomas.stuefe at gmail.com]
>> >> Sent: Freitag, 27. April 2018 09:21
>> >> To: Langer, Christoph <christoph.langer at sap.com>
>> >> Cc: Volker Simonis <volker.simonis at gmail.com>; Baesken, Matthias
>> >> <matthias.baesken at sap.com>; Simonis, Volker
>> <volker.simonis at sap.com>;
>> >> ppc-aix-port-dev at openjdk.java.net; core-libs-dev at openjdk.java.net;
>> build-
>> >> dev at openjdk.java.net
>> >> Subject: Re: RFR : 8202322: AIX: symbol visibility flags not support on xlc
>> 12.1
>> >>
>> >> Hi Christoph
>> >>
>> >> On Fri, Apr 27, 2018 at 8:07 AM, Langer, Christoph
>> >> <christoph.langer at sap.com> wrote:
>> >> > Hi Thomas,
>> >> >
>> >> > Look at this blog:
>> https://www.ibm.com/developerworks/aix/library/au-
>> >> aix-symbol-visibility-part2/index.html
>> >> >
>> >> > if I understand it correctly, the xlc 12 default behavior should be like
>> what
>> >> we'd expect from -qvisibility=hidden.
>> >> >
>> >>
>> >> Where in this article do you read this?
>> >>
>> >> ..Thomas
>> >>
>> >> > Best regards
>> >> > Christoph
>> >> >
>> >> >> -----Original Message-----
>> >> >> From: build-dev [mailto:build-dev-bounces at openjdk.java.net] On
>> Behalf
>> >> Of
>> >> >> Thomas Stüfe
>> >> >> Sent: Freitag, 27. April 2018 06:55
>> >> >> To: Volker Simonis <volker.simonis at gmail.com>; Baesken, Matthias
>> >> >> <matthias.baesken at sap.com>
>> >> >> Cc: Simonis, Volker <volker.simonis at sap.com>; ppc-aix-port-
>> >> >> dev at openjdk.java.net; core-libs-dev at openjdk.java.net; build-
>> >> >> dev at openjdk.java.net
>> >> >> Subject: Re: RFR : 8202322: AIX: symbol visibility flags not support on xlc
>> >> 12.1
>> >> >>
>> >> >> Hi,
>> >> >>
>> >> >> This was added by "8200178: Remove mapfiles for JDK native libraries".
>> >> >> But if the flag is not accepted, what is the default behavior? Do we
>> >> >> now export everything?
>> >> >>
>> >> >> I'd like to understand this first before removing the flag to get rid
>> >> >> of the warnings.
>> >> >>
>> >> >> Best Regards, Thomas
>> >> >>
>> >> >> On Thu, Apr 26, 2018 at 5:16 PM, Volker Simonis
>> >> >> <volker.simonis at gmail.com> wrote:
>> >> >> > Hi Matthias,
>> >> >> >
>> >> >> > after Bhaktavatsal Reddy's report about the problems with
>> >> >> > "-qvisibility" with xlC 13 and taking into account that we can't test
>> >> >> > this anyway because we don't currently have xlC 13
>> >> >> >  on our machines I think it would be best to completely remove this
>> >> >> > option for now on AIX. Once we get xlC 13 we can revisit the issue.
>> >> >> >
>> >> >> > Thanks,
>> >> >> > Volker
>> >> >> >
>> >> >> >
>> >> >> > On Thu, Apr 26, 2018 at 4:59 PM, Bhaktavatsal R Maram
>> >> >> > <bhamaram at in.ibm.com> wrote:
>> >> >> >> Hi Matthias,
>> >> >> >>
>> >> >> >> At this point, I think we can remove the flag as you found that it is
>> not
>> >> >> supported in XLC < 13. And with XLC 13, it require more work to use
>> this
>> >> flag.
>> >> >> >>
>> >> >> >> Thanks,
>> >> >> >> Bhaktavatsal Reddy
>> >> >> >>
>> >> >> >>
>> >> >> >>
>> >> >> >> -----"Baesken, Matthias" <matthias.baesken at sap.com> wrote: ----
>> -
>> >> >> >> To: "Langer, Christoph" <christoph.langer at sap.com>, "'build-
>> >> >> dev at openjdk.java.net'" <build-dev at openjdk.java.net>, "ppc-aix-
>> port-
>> >> >> dev at openjdk.java.net" <ppc-aix-port-dev at openjdk.java.net>, "core-
>> >> libs-
>> >> >> dev at openjdk.java.net" <core-libs-dev at openjdk.java.net>
>> >> >> >> From: "Baesken, Matthias" <matthias.baesken at sap.com>
>> >> >> >> Date: 04/26/2018 08:23PM
>> >> >> >> Cc: "Simonis, Volker" <volker.simonis at sap.com>, Bhaktavatsal R
>> >> Maram
>> >> >> <bhamaram at in.ibm.com>
>> >> >> >> Subject: RE: RFR : 8202322: AIX: symbol visibility flags not support on
>> xlc
>> >> >> 12.1
>> >> >> >>
>> >> >> >>
>> >> >> >>  Hello Christoph,   I think  all XLC versions  < 12.1   are unsupported
>> >> (and
>> >> >> probably not working anyway)  for the OpenJDK  build .
>> >> >> >>  I am only aware   of  XLC  versions  12.1  and 13.1    which  work / in
>> case
>> >> of
>> >> >> 13.1  “might” work   for OpenJDK compilation .
>> >> >> >>  And for 12.1  I want to remove the flags  .
>> >> >> >>
>> >> >> >>  ( waiting for the feedback  of   Bhaktavatsal Reddy ,  in case he
>> prefers
>> >> it
>> >> >> I remove them for all xlC versions including 13.1 )
>> >> >> >>
>> >> >> >>  Best regards, Matthias
>> >> >> >>
>> >> >> >>
>> >> >> >>
>> >> >> >>
>> >> >> >>
>> >> >> >>
>> >> >> >>  From: Langer, Christoph
>> >> >> >>  Sent: Donnerstag, 26. April 2018 16:38
>> >> >> >>  To: Baesken, Matthias <matthias.baesken at sap.com>; 'build-
>> >> >> dev at openjdk.java.net' <build-dev at openjdk.java.net>; ppc-aix-port-
>> >> >> dev at openjdk.java.net; core-libs-dev at openjdk.java.net
>> >> >> >>  Cc: Simonis, Volker <volker.simonis at sap.com>
>> >> >> >>  Subject: RE: RFR : 8202322: AIX: symbol visibility flags not support
>> on
>> >> xlc
>> >> >> 12.1
>> >> >> >>
>> >> >> >>  Hi Matthias,
>> >> >> >>
>> >> >> >>  to me the change in principal looks good.
>> >> >> >>
>> >> >> >>  I’m wondering if it is possible to do a comparison like xlc < 13 (e.g.
>> >> extract
>> >> >> major number before the first dot, then compare numerically) – but
>> >> maybe it
>> >> >> is too complicated and the current single version compare suits  our
>> needs
>> >> ?
>> >> >> >>
>> >> >> >>  Best regards
>> >> >> >>  Christoph
>> >> >> >>
>> >> >> >>
>> >> >> >>
>> >> >> >>
>> >> >> >>  From: Baesken, Matthias
>> >> >> >>  Sent: Donnerstag, 26. April 2018 16:14
>> >> >> >>  To: 'build-dev at openjdk.java.net' <build-dev at openjdk.java.net>;
>> >> ppc-
>> >> >> aix-port-dev at openjdk.java.net; core-libs-dev at openjdk.java.net
>> >> >> >>  Cc: Langer, Christoph <christoph.langer at sap.com>; Simonis,
>> Volker
>> >> >> <volker.simonis at sap.com>
>> >> >> >>  Subject: RFR : 8202322: AIX: symbol visibility flags not support on xlc
>> >> 12.1
>> >> >> >>
>> >> >> >>  Hello  ,  could you please review this small adjustment to  the
>> symbol
>> >> >> visibility compilation settings on AIX ?
>> >> >> >>  Currently  we use  XLC 12.1  to compile  JDK on AIX .
>> >> >> >>
>> >> >> >>  However XLC 12.1   does not support  the “-qvisibility=hidden”
>> setting
>> >> >> currently set on AIX.
>> >> >> >>  It was introduced with  XLC 13.1 . Christoph found some info about
>> it
>> >> here
>> >> >> :
>> >> >> >>
>> >> >> >>  https://www.ibm.com/developerworks/aix/library/au-aix-symbol-
>> >> >> visibility-part2/index.html
>> >> >> >>
>> >> >> >>  Setting it  only generates  hundreds  of warnings  in the build log ,
>> >> >> warnings look like this :
>> >> >> >>  XlC12.1
>> >> >> >>
>> >> >> >>  bash-4.4$ xlC -qversion
>> >> >> >>  IBM XL C/C++ for AIX, V12.1 (5765-J02, 5725-C72)
>> >> >> >>  Version: 12.01.0000.0019
>> >> >> >>
>> >> >> >>  bash-4.4$ xlC -qvisibility=hidden sizeof.c -o sizeof_aixxlc
>> >> >> >>  1506-173 (W) Option visibility=hidden is not valid. Enter xlC for list
>> of
>> >> valid
>> >> >> options.
>> >> >> >>
>> >> >> >>  Compare to XLC13.1
>> >> >> >>
>> >> >> >>  bash-3.00$ xlC -qversion
>> >> >> >>  IBM XL C/C++ for AIX, V13.1 (5725-C72, 5765-J07)
>> >> >> >>  Version: 13.01.0000.0008
>> >> >> >>  bash-3.00$ xlC -qvisibility=default sizeof.c -o sizeof_aixxlc
>> >> >> >>  bash-3.00$ xlC -qvisibility=hidden sizeof.c -o sizeof_aixxlc
>> >> >> >>
>> >> >> >>
>> >> >> >>  So it is better to avoid  setting these flags when using xlc12.1   .
>> >> >> >>  Please review :
>> >> >> >>
>> >> >> >>  Bug :
>> >> >> >>
>> >> >> >>  https://bugs.openjdk.java.net/browse/JDK-8202322
>> >> >> >>
>> >> >> >>  Change :
>> >> >> >>
>> >> >> >>  http://cr.openjdk.java.net/~mbaesken/webrevs/8202322/
>> >> >> >>
>> >> >> >>
>> >> >> >>  Best regards, Matthias
>> >> >> >>
>> >> >> >>
>> >> >> >>
>> >> >> >>


More information about the build-dev mailing list