[petsc-dev] Issue with dependency generation in GCC 9

[Matthew Knepley]

On Mon, Jan 20, 2020 at 3:06 AM Lisandro Dalcin <dalcinl at gmail.com> wrote:

> I'm using GCC 9 from Fedora 31. A few things have changed regarding
> dependency generation, and things are now broken for PETSc. I do not have a
> clean solution to propose.
>
> The problem is the way targets are emitted :
>
> $ head -n 3 arch-linux2-c-debug/obj/sys/objects/init.d
> init.o: /home/devel/petsc/dev/src/sys/objects/init.c \
>  /home/devel/petsc/dev/include/petscsys.h \
>  /home/devel/petsc/dev/arch-linux2-c-debug/include/petscconf.h \
>
> GCC now generates a bare "init.o" target. Using GCC 8 in a Manjaro box I
> get instead:
>
> $ head -n 3 arch-linux2-c-debug/obj/sys/objects/init.d
> arch-linux2-c-debug/obj/sys/objects/init.o: \
>  /home/devel/petsc/src/sys/objects/init.c \
>  /home/devel/petsc/include/petscsys.h \
>
> These differences totally break our use of dependencies:
>
> $ touch include/petscsys.h
> $ make
> ...
> gmake[2]: Nothing to be done for 'all'.
> ...
>
>
> My quick workaround so far has been to add this in makefiles:
>
> C_DEPFLAGS   += -MT $@
> CXX_DEPFLAGS += -MT $@
> FC_DEPFLAGS  += -MT $@
>
> From the GCC info page
>
> '-MT TARGET'
>
>      Change the target of the rule emitted by dependency generation.  By
>      default CPP takes the name of the main input file, deletes any
>      directory components and any file suffix such as '.c', and appends
>      the platform's usual object suffix.  The result is the target.
>
>      An '-MT' option sets the target to be exactly the string you
>      specify.  If you want multiple targets, you can specify them as a
>      single argument to '-MT', or use multiple '-MT' options.
>
>      For example, '-MT '$(objpfx)foo.o'' might give
>
>           $(objpfx)foo.o: foo.c
>

Why is my GCC 9.1 not doing this?

master *$:/PETSc3/petsc/petsc-dev$ head -n 3
arch-master-debug/obj/sys/objects/init.d
arch-master-debug/obj/sys/objects/init.o: \
  /PETSc3/petsc/petsc-dev/src/sys/objects/init.c \
  /PETSc3/petsc/petsc-dev/include/petscsys.h \
master *$:/PETSc3/petsc/petsc-dev$ head -n 3
arch-master-gcc-debug/obj/sys/objects/init.d
arch-master-gcc-debug/obj/sys/objects/init.o: \
 /PETSc3/petsc/petsc-dev/src/sys/objects/init.c \
 /PETSc3/petsc/petsc-dev/include/petscsys.h \
master *$:/PETSc3/petsc/petsc-dev$ /PETSc3/petsc/gcc/bin/mpicc -show
/Users/knepley/MacSoftware/bin/ccache /usr/local/gcc-9.1/bin/gcc-9.1
-fstack-protector -g3 -Wl,-flat_namespace -Wl,-commons,use_dy
libs -I/PETSc3/petsc/gcc/include -L/PETSc3/petsc/gcc/lib -lmpi -lpmpi
master *$:/PETSc3/petsc/petsc-dev$ /usr/local/gcc-9.1/bin/gcc-9.1 --version
gcc-9.1 (GCC) 9.1.0
Copyright (C) 2019 Free Software Foundation, Inc.

This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

   Matt


> --
> Lisandro Dalcin
> ============
> Research Scientist
> Extreme Computing Research Center (ECRC)
> King Abdullah University of Science and Technology (KAUST)
> http://ecrc.kaust.edu.sa/
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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