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Subject: Re: [PATCH v13 3/3] selftest/interpreter: Add tests for
 trusted_for(2) policies
To:     Kees Cook <keescook@chromium.org>
Cc:     Al Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
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        =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= <mic@linux.microsoft.com>
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Date:   Fri, 8 Oct 2021 12:21:12 +0200
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On 07/10/2021 21:48, Kees Cook wrote:
> On Thu, Oct 07, 2021 at 08:23:20PM +0200, Mickaël Salaün wrote:

[...]

>> diff --git a/tools/testing/selftests/interpreter/Makefile b/tools/testing/selftests/interpreter/Makefile
>> new file mode 100644
>> index 000000000000..1f71a161d40b
>> --- /dev/null
>> +++ b/tools/testing/selftests/interpreter/Makefile
>> @@ -0,0 +1,21 @@
>> +# SPDX-License-Identifier: GPL-2.0
>> +
>> +CFLAGS += -Wall -O2
>> +LDLIBS += -lcap
>> +
>> +src_test := $(wildcard *_test.c)
>> +TEST_GEN_PROGS := $(src_test:.c=)
>> +
>> +KSFT_KHDR_INSTALL := 1
>> +include ../lib.mk
>> +
>> +khdr_dir = $(top_srcdir)/usr/include
>> +
>> +$(khdr_dir)/asm-generic/unistd.h: khdr
>> +	@:
>> +
>> +$(khdr_dir)/linux/trusted-for.h: khdr
>> +	@:
>> +
>> +$(OUTPUT)/%_test: %_test.c $(khdr_dir)/asm-generic/unistd.h $(khdr_dir)/linux/trusted-for.h ../kselftest_harness.h
>> +	$(LINK.c) $< $(LDLIBS) -o $@ -I$(khdr_dir)
> 
> Is all this really needed?

Yes, all this is needed to be sure that the tests will be rebuild when a
dependency change (either one of the header files or a source file).

> 
> - CFLAGS and LDLIBS will be used by the default rules

Yes, but it will only run the build command when a source file change,
not a header file.

> - khdr is already a pre-dependency when KSFT_KHDR_INSTALL is set

Yes, but it is not enough to rebuild the tests (and check the installed
files) when a header file change.

> - kselftest_harness.h is already a build-dep (see LOCAL_HDRS)

Yes, but without an explicit requirement, changing kselftest_harness.h
doesn't force a rebuild.

> - TEST_GEN_PROGS's .c files are already build-deps

It is not enough to trigger test rebuilds.

> 
> kselftest does, oddly, lack a common -I when KSFT_KHDR_INSTALL is set
> (which likely should get fixed, though separately from here).
> 
> I think you just want:
> 
> 
> src_test := $(wildcard *_test.c)
> TEST_GEN_PROGS := $(src_test:.c=)
> 
> KSFT_KHDR_INSTALL := 1
> include ../lib.mk
> 
> CFLAGS += -Wall -O2 -I$(BUILD)/usr/include
> LDLIBS += -lcap
> 
> $(OUTPUT)/%_test: $(BUILD)/usr/include/linux/trusted-for.h
> 
> 
> (untested)
> 
Yep, I re-checked and my Makefile is correct. I didn't find a way to
make it lighter while correctly handling dependencies.
I'll just move the -I to CFLAGS.