Re: [PATCH v2 2/4] selftests: Fix seccomp to support relocatable build (O=objdir)

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On 3/4/20 7:20 PM, Kees Cook wrote:
On Wed, Mar 04, 2020 at 05:36:27PM -0700, Shuah Khan wrote:
Fix seccomp relocatable builds. This is a simple fix to use the
right lib.mk variable TEST_CUSTOM_PROGS to continue to do custom
build to preserve dependency on kselftest_harness.h local header.
This change applies cutom rule to seccomp_bpf seccomp_benchmark
for a simpler logic.

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

This works.


 From top level from main Makefile:
make kselftest-install O=objdir ARCH=arm64 HOSTCC=gcc \
  CROSS_COMPILE=aarch64-linux-gnu- TARGETS=seccomp

This fails for me:

$ make kselftest-install O=objdir ARCH=arm64 HOSTCC=gcc CROSS_COMPILE=aarch64-linux-gnu- TARGETS=seccomp
make[1]: Entering directory '/home/kees/src/linux/objdir'
make --no-builtin-rules INSTALL_HDR_PATH=$BUILD/usr \
         ARCH=arm64 -C ../../.. headers_install
make[4]: ../scripts/Makefile.build: No such file or directory
make[4]: *** No rule to make target '../scripts/Makefile.build'.  Stop.
make[3]: *** [Makefile:501: scripts_basic] Error 2
make[2]: *** [Makefile:151: khdr] Error 2
make[1]: *** [/home/kees/src/linux/Makefile:1221: kselftest-install] Error 2
make[1]: Leaving directory '/home/kees/src/linux/objdir'
make: *** [Makefile:180: sub-make] Error 2

(My "objdir" is empty)

If I remove O=objdir everything is fine. And see below...

Signed-off-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
---
  tools/testing/selftests/seccomp/Makefile | 19 +++++++++----------
  1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/seccomp/Makefile b/tools/testing/selftests/seccomp/Makefile
index 1760b3e39730..355bcbc0394a 100644
--- a/tools/testing/selftests/seccomp/Makefile
+++ b/tools/testing/selftests/seccomp/Makefile
@@ -1,17 +1,16 @@
  # 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_CUSTOM_PROGS := $(OUTPUT)/seccomp_bpf $(OUTPUT)/seccomp_benchmark
-seccomp_bpf: seccomp_bpf.c ../kselftest_harness.h
-	$(CC) $(CFLAGS) $(LDFLAGS) $< -lpthread -o $@
+$(TEST_CUSTOM_PROGS): ../kselftest_harness.h
-TEST_PROGS += $(BINARIES)
-EXTRA_CLEAN := $(BINARIES)
+all: $(TEST_CUSTOM_PROGS)
-all: $(BINARIES)
+EXTRA_CLEAN := $(TEST_CUSTOM_PROGS)
--
2.20.1


Instead of the TEST_CUSTOM_PROGS+all dance, you can just add an explicit
dependency, with the final seccomp/Makefile looking like this:


# SPDX-License-Identifier: GPL-2.0
CFLAGS += -Wl,-no-as-needed -Wall
LDFLAGS += -lpthread

TEST_GEN_PROGS := seccomp_bpf seccomp_benchmark


TEST_CUSTOM_PROGS is for differentiating test programs that
can't use lib.mk generic rules. It is appropriate to use
for seccomp_bpf

include ../lib.mk

# Additional dependencies
$(OUTPUT)/seccomp_bpf: ../kselftest_harness.h


(Though this fails in the same way as above when run from the top-level
directory.)


I didn't see this because I have been the same directory I used
for relocated cross-build kernel. :(

Thanks for testing this. I know the problem here. all is a dependency
for install step and $(OUTPUT) is referencing the objdir before it
gets created. It is a Makefile/lib.mk problem to fix.

I will do a separate patch for this. This will show up in any test
that is using $(OUTPUT) to relocate objects mainly the ones that
require custom build rule like seeccomp.

thanks,
-- Shuah




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