Re: [PATCH][gcc-4.9.0] gcc/Makefile.in: fix parallel building failure

[Hongxu Jia <hongxu dot jia at windriver dot com>]

On 07/24/2014 12:17 PM, Andrew Pinski wrote:
> On Wed, Jul 23, 2014 at 9:10 PM, Hongxu Jia <hongxu.jia@windriver.com> wrote:
> > 1. How to reproduce the issue:
> >
> > 1) manually modify gcc/Makefile.in to delay the generation of config.h:
> > ...
> > diff --git gcc-4.9.0/gcc/Makefile.in gcc-4.9.0/gcc/Makefile.in
> > --- gcc-4.9.0/gcc/Makefile.in
> > +++ gcc-4.9.0/gcc/Makefile.in
> > @@ -1622,9 +1622,12 @@ tm.h: cs-tm.h ; @true
> >   tm_p.h: cs-tm_p.h ; @true
> >
> >   cs-config.h: Makefile
> > +   @echo "start to generate config.h `date`"
> > +   sleep 10
> >      TARGET_CPU_DEFAULT="" \
> >      HEADERS="$(host_xm_include_list)" DEFINES="$(host_xm_defines)" \
> >      $(SHELL) $(srcdir)/mkconfig.sh config.h
> > +   @echo "config.h generated `date`"
> >
> >   cs-bconfig.h: Makefile
> >      TARGET_CPU_DEFAULT="" \
> > ...
> >
> > 2) compiling gcc
> >
> > 2. Analysis
> >
> > Most C source files included config.h which was generated by a rule.
> > But no related prerequisites was added to the C source compiling rule.
> > There was potential building failure while makefile enabled parallel.
>
> Why not update the dependencies instead of this hack?
> For 4.10/5.0 is this already fixed by changing how dependencies work.

Hi Andrew,

I tests on 4.10 (gcc-4.10-20140720), and this issue still existed.

After a grep in gcc subdir, there are almost 703 C source files included 
config.h,

How to add dependencies? I am not familar with this.

Thanks,
Hongxu


> Thanks,
> Andrew
>
> > The C source compiling rule used suffix rule '.c.o', but the suffix
> > rule doesn't support prerequisites.
> > https://www.gnu.org/software/make/manual/html_node/Suffix-Rules.html
> >
> > We used the pattern rule '%.o : %.c' to instead, and add the config.h
> > as its prerequisite
> >
> > We also moved the '%.o : %.c' rule down to the 'build/%.o :' rule, which
> > makes '%.o : %.c' rule doesn't override 'build/%.o :'.
> >
> > For more detail:
> > https://bugzilla.yoctoproject.org/show_bug.cgi?id=6568
> >
> > Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
> > ---
> >   gcc/Makefile.in | 12 ++++++++----
> >   1 file changed, 8 insertions(+), 4 deletions(-)
> >
> > diff --git gcc-4.9.0/gcc/Makefile.in gcc-4.9.0/gcc/Makefile.in
> > index 6475cba..04889fe 100644
> > --- gcc-4.9.0/gcc/Makefile.in
> > +++ gcc-4.9.0/gcc/Makefile.in
> > @@ -1054,10 +1054,6 @@ COMPILE = source='$<' object='$@' libtool=no \
> >   POSTCOMPILE =
> >   endif
> >
> > -.cc.o .c.o:
> > -       $(COMPILE) $<
> > -       $(POSTCOMPILE)
> > -
> >   #
> >   # Support for additional languages (other than C).
> >   # C can be supported this way too (leave for later).
> > @@ -2342,6 +2338,14 @@ build/%.o :  # dependencies provided by explicit rule later
> >          $(COMPILER_FOR_BUILD) -c $(BUILD_COMPILERFLAGS) $(BUILD_CPPFLAGS) \
> >                  -o $@ $<
> >
> > +%.o: %.c $(CONFIG_H)
> > +       $(COMPILE) $<
> > +       $(POSTCOMPILE)
> > +
> > +%.o: %.cc $(CONFIG_H)
> > +       $(COMPILE) $<
> > +       $(POSTCOMPILE)
> > +
> >   ## build/version.o is compiled by the $(COMPILER_FOR_BUILD) but needs
> >   ## several C macro definitions, just like version.o
> >   build/version.o:  version.c version.h \
> > --
> > 1.8.1.2