linux-kernel - Re: [PATCH 2/8] selftests/vm: use a common gup

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Date:   Tue, 29 Sep 2020 10:44:31 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Shuah Khan <shuah@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-kselftest@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-s390@...r.kernel.org>
Subject: Re: [PATCH 2/8] selftests/vm: use a common gup_test.h

On 9/29/20 9:35 AM, Jason Gunthorpe wrote:
> On Mon, Sep 28, 2020 at 01:10:24PM -0700, John Hubbard wrote:
>> On 9/28/20 5:57 AM, Jason Gunthorpe wrote:
>>> On Sun, Sep 27, 2020 at 11:21:53PM -0700, John Hubbard wrote:
>>>> diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile
>>>> index d1ae706d9927..9cc6bc087461 100644
>>>> +++ b/tools/testing/selftests/vm/Makefile
>>>> @@ -130,3 +130,5 @@ endif
>>>>    $(OUTPUT)/userfaultfd: LDLIBS += -lpthread
>>>>    $(OUTPUT)/mlock-random-test: LDLIBS += -lcap
>>>> +
>>>> +$(OUTPUT)/gup_test: ../../../../mm/gup_test.h
>>>
>>> There is no reason to do this, the auto depends will pick up header
>>> files, and gup_test.h isn't a generated file
>>>

Oh, I misread your comment! You were talking about this Makefile
dependency that I'm adding, rather than the ../'s in the path.

Well, for that though, it also has to stay as shown in this patch,
because of this:

I don't see any "gcc -m" type of dependency generation pass happening
in this relatively simple Make system. And so, without including an
explicit header file dependency (at least, that's the simplest way),
changes to gup_test.h are not detected. Both the Makefile code and the
observed behavior back this up. (I expect that this is because there is
less use of header files in this area, because most unit tests are
self-contained within a single .c file.)


>>
>> It is less capable than you might think. Without the admittedly ugly technique
>> above, it fails to build, and as you can see, the include paths that are fed to
>> gcc are just a single one: usr/include:
>>
>> $ make
>> make --no-builtin-rules ARCH=x86 -C ../../../.. headers_install
>> gcc -Wall -I ../../../../usr/include     gup_test.c
>> /kernel_work/linux-next-github/tools/testing/selftests/kselftest_harness.h
>> /kernel_work/linux-next-github/tools/testing/selftests/kselftest.h
>> ../../../../mm/gup_test.h -lrt -o
>> /kernel_work/linux-next-github/tools/testing/selftests/vm/gup_test
>> make[1]: Entering directory '/kernel_work/linux-next-github'
>> gup_test.c:10:10: fatal error: gup_test.h: No such file or directory
>>     10 | #include "gup_test.h"
>>        |          ^~~~~~~~~~~~
> 
> You are supposed to use
> 
>    #include "../../../../mm/gup_test.h"

Good, I'll leave it as I had it.


> I have no idea what weird behavior the makefile is triggering that the
> above include works
> 

See the commit description for yet another Makefile weird behavior point. :)

thanks,
-- 
John Hubbard
NVIDIA