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

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Date:   Mon, 16 Mar 2020 23:12:57 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Shuah Khan <skhan@...uxfoundation.org>, shuah@...nel.org,
        keescook@...omium.org, luto@...capital.net, wad@...omium.org,
        daniel@...earbox.net, kafai@...com, yhs@...com, andriin@...com,
        gregkh@...uxfoundation.org, tglx@...utronix.de
Cc:     Shuah Khan <skhan@...uxfoundation.org>, khilman@...libre.com,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH v3] selftests: Fix seccomp to support relocatable build (O=objdir)

Shuah Khan <skhan@...uxfoundation.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@...uxfoundation.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


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