Re: [PATCH v3] selftests: Fix seccomp to support relocatable build (O=objdir)

[Kees Cook <keescook@chromium.org>]

On Mon, Mar 16, 2020 at 11:12:57PM +1100, Michael Ellerman wrote:
> Shuah Khan <skhan@linuxfoundation.org> writes:
> > Fix seccomp relocatable builds. This is a simple fix to use the right
> > lib.mk variable TEST_GEN_PROGS with dependency on kselftest_harness.h
> > header, and defining LDFLAGS for pthread lib.
> >
> > Removes custom clean rule which is no longer necessary with the use of
> > TEST_GEN_PROGS. 
> >
> > Uses $(OUTPUT) defined in lib.mk to handle build relocation.
> >
> > The following use-cases work with this change:
> >
> > In seccomp directory:
> > make all and make clean
> >
> > From top level from main Makefile:
> > make kselftest-install O=objdir ARCH=arm64 HOSTCC=gcc \
> >  CROSS_COMPILE=aarch64-linux-gnu- TARGETS=seccomp
> >
> > Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
> > ---
> >
> > Changes since v2:
> > -- Using TEST_GEN_PROGS is sufficient to generate objects.
> >    Addresses review comments from Kees Cook.
> >
> >  tools/testing/selftests/seccomp/Makefile | 18 ++++++++----------
> >  1 file changed, 8 insertions(+), 10 deletions(-)
> >
> > diff --git a/tools/testing/selftests/seccomp/Makefile b/tools/testing/selftests/seccomp/Makefile
> > index 1760b3e39730..a0388fd2c3f2 100644
> > --- a/tools/testing/selftests/seccomp/Makefile
> > +++ b/tools/testing/selftests/seccomp/Makefile
> > @@ -1,17 +1,15 @@
> >  # SPDX-License-Identifier: GPL-2.0
> > -all:
> > -
> > -include ../lib.mk
> > +CFLAGS += -Wl,-no-as-needed -Wall
> > +LDFLAGS += -lpthread
> >  
> >  .PHONY: all clean
> >  
> > -BINARIES := seccomp_bpf seccomp_benchmark
> > -CFLAGS += -Wl,-no-as-needed -Wall
> > +include ../lib.mk
> > +
> > +# OUTPUT set by lib.mk
> > +TEST_GEN_PROGS := $(OUTPUT)/seccomp_bpf $(OUTPUT)/seccomp_benchmark
> >  
> > -seccomp_bpf: seccomp_bpf.c ../kselftest_harness.h
> > -	$(CC) $(CFLAGS) $(LDFLAGS) $< -lpthread -o $@
> > +$(TEST_GEN_PROGS): ../kselftest_harness.h
> >  
> > -TEST_PROGS += $(BINARIES)
> > -EXTRA_CLEAN := $(BINARIES)
> > +all: $(TEST_GEN_PROGS)
> >  
> > -all: $(BINARIES)
> 
> 
> It shouldn't be that complicated. We just need to define TEST_GEN_PROGS
> before including lib.mk, and then add the dependency on the harness
> after we include lib.mk (so that TEST_GEN_PROGS has been updated to
> prefix $(OUTPUT)).
> 
> eg:
> 
>   # SPDX-License-Identifier: GPL-2.0
>   CFLAGS += -Wl,-no-as-needed -Wall
>   LDFLAGS += -lpthread
>   
>   TEST_GEN_PROGS := seccomp_bpf seccomp_benchmark
>   
>   include ../lib.mk
>   
>   $(TEST_GEN_PROGS): ../kselftest_harness.h

Exactly. This (with an extra comment) is precisely what I suggested during
v2 review:
https://lore.kernel.org/lkml/202003041815.B8C73DEC@keescook/

-Kees

> 
> 
> Normal in-tree build:
> 
>   selftests$ make TARGETS=seccomp
>   make[1]: Entering directory '/home/michael/linux/tools/testing/selftests/seccomp'
>   gcc -Wl,-no-as-needed -Wall  -lpthread  seccomp_bpf.c ../kselftest_harness.h  -o /home/michael/linux/tools/testing/selftests/seccomp/seccomp_bpf
>   gcc -Wl,-no-as-needed -Wall  -lpthread  seccomp_benchmark.c ../kselftest_harness.h  -o /home/michael/linux/tools/testing/selftests/seccomp/seccomp_benchmark
>   make[1]: Leaving directory '/home/michael/linux/tools/testing/selftests/seccomp'
>   
>   selftests$ ls -l seccomp/
>   total 388
>   -rw-rw-r-- 1 michael michael     41 Jan  9 12:00 config
>   -rw-rw-r-- 1 michael michael    201 Mar 16 23:04 Makefile
>   -rwxrwxr-x 1 michael michael  70824 Mar 16 23:07 seccomp_benchmark*
>   -rw-rw-r-- 1 michael michael   2289 Feb 17 21:39 seccomp_benchmark.c
>   -rwxrwxr-x 1 michael michael 290520 Mar 16 23:07 seccomp_bpf*
>   -rw-rw-r-- 1 michael michael  94778 Mar  5 23:33 seccomp_bpf.c
> 
> 
> O= build:
> 
>   selftests$ make TARGETS=seccomp O=$PWD/build
>   make[1]: Entering directory '/home/michael/linux/tools/testing/selftests/seccomp'
>   gcc -Wl,-no-as-needed -Wall  -lpthread  seccomp_bpf.c ../kselftest_harness.h  -o /home/michael/linux/tools/testing/selftests/build/seccomp/seccomp_bpf
>   gcc -Wl,-no-as-needed -Wall  -lpthread  seccomp_benchmark.c ../kselftest_harness.h  -o /home/michael/linux/tools/testing/selftests/build/seccomp/seccomp_benchmark
>   make[1]: Leaving directory '/home/michael/linux/tools/testing/selftests/seccomp'
>   
>   selftests$ ls -l build/seccomp/
>   total 280
>   -rwxrwxr-x 1 michael michael  70824 Mar 16 23:05 seccomp_benchmark*
>   -rwxrwxr-x 1 michael michael 290520 Mar 16 23:05 seccomp_bpf*
> 
> 
> Build in the directory itself:
>   selftests$ cd seccomp
>   seccomp$ make
>   gcc -Wl,-no-as-needed -Wall  -lpthread  seccomp_bpf.c ../kselftest_harness.h  -o /home/michael/linux/tools/testing/selftests/seccomp/seccomp_bpf
>   gcc -Wl,-no-as-needed -Wall  -lpthread  seccomp_benchmark.c ../kselftest_harness.h  -o /home/michael/linux/tools/testing/selftests/seccomp/seccomp_benchmark
>   
>   seccomp$ ls -l
>   total 388
>   -rw-rw-r-- 1 michael michael     41 Jan  9 12:00 config
>   -rw-rw-r-- 1 michael michael    201 Mar 16 23:04 Makefile
>   -rwxrwxr-x 1 michael michael  70824 Mar 16 23:06 seccomp_benchmark*
>   -rw-rw-r-- 1 michael michael   2289 Feb 17 21:39 seccomp_benchmark.c
>   -rwxrwxr-x 1 michael michael 290520 Mar 16 23:06 seccomp_bpf*
>   -rw-rw-r-- 1 michael michael  94778 Mar  5 23:33 seccomp_bpf.c
> 
> 
> cheers

-- 
Kees Cook