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

Kees Cook [off-list ref] writes:

On Mon, Mar 16, 2020 at 11:12:57PM +1100, Michael Ellerman wrote:

quoted

Shuah Khan [off-list ref] writes:

quoted

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/ (local)

Oh sorry, I missed that.

OK so I think we know what the right solution is.

cheers