RFR: 8236714: enable link-time section-gc for linux to remove unused code

[Baesken, Matthias]

Hi Erik, thanks for the review and for forwarding ,  you are correct  corelibs-dev is probably  interested in this as well .

Best regards, Matthias


> (adding core-libs-dev)
> 
> Change looks good to me, but would like input from at least someone in
> core-libs.
> 
> /Erik
> 
> On 2020-01-14 06:07, Baesken, Matthias wrote:
> > Hello,  the following change enables the  link-time section-gc for linux .
> >
> > gcc and ld support enabling "garbage collection" of unused input sections.
> > This can be used to eliminate unused coding from native libraries
> (especially when already compiling the objects with compiler flags -ffunction-
> sections -fdata-sections .
> > See for details the --gc-sections and --print-gc-sections parts of the ld
> documentation :
> >
> > https://linux.die.net/man/1/ld
> >
> >
> > We had this enabled already  for  linux s390x ,  with
> https://bugs.openjdk.java.net/browse/JDK-8234525
> > 8234525: enable link-time section-gc for linux s390x to remove unused code
> .
> >
> > This  time we enable it too for  the other linux platforms .
> >
> > For the other platforms I do not enable it for JVM, just for the JDK libs.  The
> reason is that the serviceability agent  (not supported on linux s390x )    is not
> (yet) ready for the optimization .
> > Below you see the results , for some libraries  a significant  size reduction
> can be achieved .
> >
> >
> > Results from linux x86_64 product builds :
> >
> > without / with ltgc
> >
> > 320K / 300K    /images/jdk/lib/libsunec.so       <-------------------------
> > 36K  / 36K     /images/jdk/lib/libdt_socket.so
> > 280K / 276K   /images/jdk/lib/libjdwp.so
> > 23M  / 23M    /images/jdk/lib/server/libjvm.so    <---- not set for libjvm.so
> for x86_64
> > 16K  / 16K    /images/jdk/lib/server/libjsig.so
> > 72K  / 72M    /images/jdk/lib/libverify.so
> > 84K  / 84M   /images/jdk/lib/libjli.so
> > 16K  / 16K    /images/jdk/lib/libjsig.so
> > 196K / 196K   /images/jdk/lib/libjava.so
> > 44K  / 44K    /images/jdk/lib/libzip.so
> > 144K / 136K   /images/jdk/lib/libjimage.so
> > 112K / 112K   /images/jdk/lib/libnet.so
> > 100K / 100K   /images/jdk/lib/libnio.so
> > 36K  / 36K    /images/jdk/lib/libsctp.so
> > 576K / 556K   /images/jdk/lib/libmlib_image.so
> > 752K / 752K   /images/jdk/lib/libawt.so
> > 260K / 252K   /images/jdk/lib/libjavajpeg.so
> > 784K / 784K   /images/jdk/lib/libfreetype.so
> > 368K / 236K /images/jdk/lib/libsplashscreen.so   <-------------------------
> > 88K / 88K    /images/jdk/lib/libjsound.so
> > 472K / 468K    /images/jdk/lib/libawt_xawt.so
> > 564K / 404K   /images/jdk/lib/liblcms.so         <--------------------------
> > 48K / 48K    /images/jdk/lib/libawt_headless.so
> > 12K / 12K    /images/jdk/lib/libjawt.so
> > 1.5M / 900K   /images/jdk/lib/libfontmanager.so  <------------------------------
> > 12K / 12K    /images/jdk/lib/libjaas.so
> > 92K / 92K    /images/jdk/lib/libj2pkcs11.so
> > 16K / 16K    /images/jdk/lib/libattach.so
> > 8.0K / 8.0K   /images/jdk/lib/librmi.so
> > 56K / 56K    /images/jdk/lib/libinstrument.so
> > 16K / 16K    /images/jdk/lib/libprefs.so
> > 52K / 52K    /images/jdk/lib/libj2gss.so
> > 12K / 12K    /images/jdk/lib/libmanagement_agent.so
> > 36K / 32K    /images/jdk/lib/libmanagement.so
> > 16K / 16K    /images/jdk/lib/libextnet.so
> > 20K / 20K    /images/jdk/lib/libj2pcsc.so
> > 40K / 40K    /images/jdk/lib/libmanagement_ext.so
> > 60K / 60K    /images/jdk/lib/libsaproc.so
> >
> >
> > Bug/webrev :
> >
> > https://bugs.openjdk.java.net/browse/JDK-8236714
> >
> > http://cr.openjdk.java.net/~mbaesken/webrevs/8236714.2/
> >
> >
> > Thanks, Matthias