Re: building gcc against eclipse?

[Andrew Haley <aph at redhat dot com>]

Jack Howarth wrote:
> On Thu, Nov 12, 2009 at 05:11:57PM +0000, Andrew Haley wrote:
> > Jack Howarth wrote:
> > > On Tue, Nov 10, 2009 at 10:00:29AM +0000, Andrew Haley wrote:
> > > > Jack Howarth wrote:
> > > > >    In fink, we have been building the gcj ecj1 support by
> > > > > copying the ecj-latest.jar file from ftp://sourceware.org/pub/java
> > > > > into the top level of the gcc source directory. I would like to try
> > > > > building gcc on darwin with the eclipse compiler instead. We have
> > > > > a fink ecj package which provides...
> > > > >
> > > > > /.
> > > > > /sw
> > > > > /sw/bin
> > > > > /sw/bin/ecj
> > > > > /sw/share
> > > > > /sw/share/doc
> > > > > /sw/share/doc/ecj
> > > > > /sw/share/doc/ecj/about.html
> > > > > /sw/share/java
> > > > > /sw/share/java/ecj
> > > > > /sw/share/java/ecj/ecj.jar
> > > > >
> > > > > How exactly does one build the gcj against this ecj compiler? Would 
> > > > > creating a symlink in the toplevel gcc directory to
> > > > > /sw/share/java/ecj/ecj.jar be sufficient to cause the installed
> > > > > eclipse compiler to be used for ecj1?
> > > > We configure for Fedora with --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
> > > > You don't have to copy that jar into the toplev of srcdir.
> > >    Would there be any possible differences in the code execution of gcj when built
> > > with the stock ftp://sourceware.org/pub/java/ecj-latest.jar compared to the ecj.jar
> > > from eclipse? My initial attempts at building a usable gcj with eclipse's ecj.jar
> > > failed due to undefined symbols for org.eclipse.jdt.internal.compiler.batch.GCCMain
> > > at runtime for ecj1. 
> > You mean the class org.eclipse.jdt.internal.compiler.batch.GCCMain is missing, I guess?
> >
> > >   I noticed that the fedora 12 gcc specfile at...
> > >
> > > http://cvs.fedoraproject.org/viewvc/rpms/gcc/F-12/gcc.spec?revision=1.90&view=markup
> > >
> > > has a section...
> > >
> > >         %if %{build_java}
> > >         %if !%{bootstrap_java}
> > >         # If we don't have gjavah in $PATH, try to build it with the old gij
> > >         mkdir java_hacks
> > >         cd java_hacks
> > >         cp -a ../../libjava/classpath/tools/external external
> > >         mkdir -p gnu/classpath/tools
> > >         cp -a ../../libjava/classpath/tools/gnu/classpath/tools/{common,javah,getopt} gnu/classpath/tools/
> > >         cp -a ../../libjava/classpath/tools/resource/gnu/classpath/tools/common/Messages.properties gnu/classpath/tools/common
> > >         cp -a ../../libjava/classpath/tools/resource/gnu/classpath/tools/getopt/Messages.properties gnu/classpath/tools/getopt
> > >         cd external/asm; for i in `find . -name \*.java`; do gcj --encoding ISO-8859-1 -C $i -I.; done; cd ../..
> > >         for i in `find gnu -name \*.java`; do gcj -C $i -I. -Iexternal/asm/; done
> > >         gcj -findirect-dispatch -O2 -fmain=gnu.classpath.tools.javah.Main -I. -Iexternal/asm/ `find . -name \*.class` -o gjavah.r
> > > eal
> > >         cat > gjavah <<EOF
> > >         #!/bin/sh
> > >         export CLASSPATH=`pwd`${CLASSPATH:+:$CLASSPATH}
> > >         exec `pwd`/gjavah.real "\$@"
> > >         EOF
> > >         chmod +x `pwd`/gjavah
> > >         cat > ecj1 <<EOF
> > >         #!/bin/sh
> > >         exec gij -cp /usr/share/java/eclipse-ecj.jar org.eclipse.jdt.internal.compiler.batch.GCCMain "\$@"
> > >         EOF
> > >         chmod +x `pwd`/ecj1
> > >         export PATH=`pwd`${PATH:+:$PATH}
> > >         cd ..
> > >         %endif
> > >         %endif
> > >
> > > This would be difficult to implement in fink for darwin since we don't have legacy gij/gcj compiler to
> > > leverage from the system compilers. Is there another way to get around the issue of the undefined
> > > org.eclipse.jdt.internal.compiler.batch.GCCMain symbol in ejc1 when using the ecj.jar from eclipse?
> > Sure.  Just put the file GCCMain.class in someDirectory, and run ecj1 as
> >
> > #!/bin/sh
> > exec gij -cp someDirectory:/usr/share/java/eclipse-ecj.jar org.eclipse.jdt.internal.compiler.batch.GCCMain "\$@"

>    If I want to have gcj automatically run this shell script of ecj1, would I just create a java_hacks
> subdirectory in the main build directory and place the ecj1 shell script in there?

There are several things going on here.

The most important difference is that Fedora builds everything fro java source:
it doesn't use the .class files that are in the gcc sources.  So, it has a much
more difficult time.

> I am very unclear if
> this java_hacks directory usage is specific to Fedora/Redhat or if it is a real feature of the gcc java
> build process. If so, is there any documentation on how the java_hacks option works?

It's just some fedora weirdness.  Don't worry about it.

ecj1 is first built in libgcj (as ecjx) and then installed in the install dir.
ecjx is renamed to ecj1 with:

if BUILD_ECJ1
## Undo any prepending of the target prefix and transform
## to the actual host's executable suffix.
	mv $(DESTDIR)$(libexecsubdir)/`echo ecjx | sed 's,^.*/,,;$(transform);s/$$/$(EXEEXT)/'` $(DESTDIR)$(libexecsubdir)/ecj1$(host_exeext)
endif BUILD_ECJ1

If you want to replace ecjx with some shell script that runs eclipse-ecj.jar,
replace this command with something appropriate.

Andrew.