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

[Shuah Khan <skhan@linuxfoundation.org>]

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@linuxfoundation.org>
>> ---
>>   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