netdev - Re: [PATCH v1 bpf-next] selftests/bpf : Clean up feature/ when make clean

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Date:   Mon, 10 Jun 2019 23:37:10 +0000
From:   Song Liu <songliubraving@...com>
To:     Hechao Li <hechaol@...com>
CC:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH v1 bpf-next] selftests/bpf : Clean up feature/ when make
 clean



> On Jun 10, 2019, at 12:02 PM, Hechao Li <hechaol@...com> wrote:
> 
> Andrii Nakryiko <andrii.nakryiko@...il.com> wrote on Mon [2019-Jun-10 11:05:28 -0700]:
>> On Mon, Jun 10, 2019 at 9:57 AM Hechao Li <hechaol@...com> wrote:
>>> 
>>> I got an error when compiling selftests/bpf:
>>> 
>>> libbpf.c:411:10: error: implicit declaration of function 'reallocarray';
>>> did you mean 'realloc'? [-Werror=implicit-function-declaration]
>>>  progs = reallocarray(progs, nr_progs + 1, sizeof(progs[0]));
>>> 
>>> It was caused by feature-reallocarray=1 in FEATURE-DUMP.libbpf and it
>>> was fixed by manually removing feature/ folder. This diff adds feature/
>>> to EXTRA_CLEAN to avoid this problem.
>>> 
>>> Signed-off-by: Hechao Li <hechaol@...com>
>>> ---
>> 
>> There is no need to include v1 into patch prefix for a first version
>> of a patch. Only v2 and further versions are added.
>> 
>> 
>>> tools/testing/selftests/bpf/Makefile | 3 ++-
>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>> 
>>> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
>>> index 2b426ae1cdc9..44fb61f4d502 100644
>>> --- a/tools/testing/selftests/bpf/Makefile
>>> +++ b/tools/testing/selftests/bpf/Makefile
>>> @@ -279,4 +279,5 @@ $(OUTPUT)/verifier/tests.h: $(VERIFIER_TESTS_DIR) $(VERIFIER_TEST_FILES)
>>>                 ) > $(VERIFIER_TESTS_H))
>>> 
>>> EXTRA_CLEAN := $(TEST_CUSTOM_PROGS) $(ALU32_BUILD_DIR) \
>>> -       $(VERIFIER_TESTS_H) $(PROG_TESTS_H) $(MAP_TESTS_H)
>>> +       $(VERIFIER_TESTS_H) $(PROG_TESTS_H) $(MAP_TESTS_H) \
>>> +       feature

I think this makes sense (before we find a better solution). Folder
feature is already in .gitignore, we know it can be removed. 

Thanks,
Song

>> 
>> It doesn't seem any of linux's Makefile do that. From brief reading of
>> build/Makefile.feature, it seems like it is supposed to handle
>> transparently the case where environment changes and thus a set of
>> supported features changes. I also verified that FEATURE-DUMP.libbpf
>> is re-generated every single time I run make in
>> tools/testing/selftests/bpf, even if nothing changed at all. So I
>> don't think this patch is necessary.
>> 
>> I'm not sure what was the cause of your original problem, though.
>> 
>>> --
>>> 2.17.1
>>> 
> 
> # Background:
> 
> My default GCC version is 4.8.5, which caused the following error when I
> run make under selftests/bpf:
> libbpf.c:39:10: fatal error: libelf.h: No such file or directory
> 
> To fix it, I have to run:
> 
> make CC=<Path to GCC 7.x>
> 
> The I got reallocarray not found error. By deleting feature/ folder
> under selftests/bpf, it was fixed.
> 
> # Root Cause:
> 
> Now I found the root cause. When I run "make", which uses GCC 4.8.5, it
> generates feature/test-reallocarray.d which indicates reallocarray is
> enabled. However, when I switched to GCC 7.0, this file was not
> re-generated and thus even FEATURE-DUMP.libbpf was re-generated, 
> feature-reallocarray is still 1 in it.
> 
> This can be reproduced by the following steps:
> $ cd tools/testing/selftests/bpf
> $ make clean && make CC=<Path to GCC 4.8.5>
> (Fail due to libelf.h not found)
> $ make clean && make CC=<Path to GCC 7.x>
> (Should succeed but actually fail with reallocarray not defined)
> 
> If adding feature to EXTRA_CLEAN is not the way to go, do you have any
> suggestion to fix such problem? I spent some time debugging this and I
> hope to fix it so that other people with similar situation won't have to
> waste time on this issue.
> 
> Thanks,
> Hechao