Re: [RFC PATCH v9 02/50] tools build: Add feature check for eBPF API

["Wangnan (F)" <wangnan0@huawei.com>]

On 2015/6/30 22:34, Arnaldo Carvalho de Melo wrote:
> Em Tue, Jun 30, 2015 at 10:29:08AM +0800, Wangnan (F) escreveu:
>> On 2015/6/30 3:41, Arnaldo Carvalho de Melo wrote:
>>>> So, what should I do now? I want to have that OFF line turned to "on",
>>>> so that I can test this stuff.
>>>> But the changelog says nothing about it, lemme check the cover letter,
>>>> but having to do that is annoying, one expects to have instructions
>>>> related to some specific changeset in its comments...
>>> So, when such build tests fail, we can see why by looking for a file
>>> with a special name in the O= output dir:
>>> [acme@felicio linux]$ cat /tmp/build/perf/feature/test-bpf.make.output
>>> test-bpf.c:1:23: fatal error: linux/bpf.h: No such file or directory
>>>   #include <linux/bpf.h>
>>>                         ^
>>> compilation terminated.
>>> [acme@felicio linux]$
>   
>> This patch tries to check the version of bpf.h, because old bpf.h doesn't
>> define 'kern_version' field for 'union bpf_attr'.
> Ok, I realise it needs to find some bpf.h file, but where should it look
> for it? What needs to be installed so that this feature test succeeds?
>   
>> I think the problem you meet is caused by missing of kernel headers in your
>> host system environment. After patch 'perf tools: Make perf depend on
>> libbpf'
> What is precise path to this bpf.h file? What was the cset that
> introduced it and in what upstream branch is it?

The exact bpf.h patch 2/50 trying to find should be 
/usr/include/linux/bpf.h, which
can be found from /tmp/build/perf/feature/test-bpf.d:

/tmp/build/perf/feature/test-bpf.bin: test-bpf.c \
  /usr/include/stdc-predef.h \
  /usr/include/bits/predefs.h \
  /usr/include/linux/bpf.h \
  /usr/include/linux/types.h \
  ....

After applying 3/50, due to the setting of FEATURE_CHECK_CFLAGS-bpf, it
becomes /path/to/kernel/include/uapi/linux/bpf.h, so it won't fail again:

/tmp/build/bpf/feature/test-bpf.bin: test-bpf.c \
  /usr/include/stdc-predef.h \
  /usr/include/bits/predefs.h \
  /path/to/kernel/include/uapi/linux/bpf.h \
  /path/to/kernel/tools/include/linux/types.h \
  ...

>> this checking should always success because it adds required headers
>> into MANIFEST and setup FEATURE_CHECK_CFLAGS-bpf.
>>
>> Also, after applying 3/50 you should see this:
> IIRC I tried yesterday, will try again later and let you know, but
> when introducing a feature test, please state what is required to be
> installed in a system so that it can succeed, where to obtain it, etc.
>
> It is possible to figure this out, but sometimes doing that takes time
> that would be beter invested in processing further patches...
>
> - Arnaldo
>   
>> # make O=/tmp/build/bpf/ -C tools/lib/bpf/
>   
>> Auto-detecting system features:
>> ...                        libelf: [ on  ]
>> ...             libelf-getphdrnum: [ on  ]
>> ...                   libelf-mmap: [ on  ]
>> ...                           bpf: [ on  ]
>>
>> make: Entering directory `/home/wn/kernel-hydrogen/tools/lib/bpf'
>>    CC       /tmp/build/bpf/libbpf.o
>>    LD       /tmp/build/bpf/libbpf-in.o
>>    LINK     /tmp/build/bpf/libbpf.a
>>    LINK     /tmp/build/bpf/libbpf.so
>> make: Leaving directory `/home/wn/kernel/tools/lib/bpf'
>>
>> Even if in perf checking bpf should fail in your machine now, checking bpf
>> feature in
>> libbpf should success because when build libbpf I have added following
>> setting to
>> tools/lib/bpf/Makefile:
>>
>>    INCLUDES = -I. -I$(srctree)/tools/include
>> -I$(srctree)/arch/$(ARCH)/include/uapi -I$(srctree)/include/uapi
>>    FEATURE_CHECK_CFLAGS-bpf = $(INCLUDES)
>>
>> Do you want me to squash 2/30 and 3/50 together and append 'bpf' checker
>> into FEATURE_TESTS in
>> tools/build/Makefile.feature in 23/50? Then there should be less confusion:
>> when compiling perf
>> before 23/50, bpf feature will never be checked then.
>>
>> Thank you.
>>
>>> Right, one of the few things that could explain the failure, but:
>>>
>>> [acme@felicio linux]$ find . -name bpf.h
>>> ./include/linux/bpf.h
>>> ./include/uapi/linux/bpf.h
>>> [acme@felicio linux]$
>>>
>>> So lemme try doing it in place:
>>>
>>> [acme@felicio linux]$ make -C tools/perf/
>>> make: Entering directory `/home/acme/git/linux/tools/perf'
>>>    BUILD:   Doing 'make -j4' parallel build
>>>
>>> Auto-detecting system features:
>>> ...                         dwarf: [ on  ]
>>> ...                         glibc: [ on  ]
>>> ...                          gtk2: [ on  ]
>>> ...                      libaudit: [ on  ]
>>> ...                        libbfd: [ on  ]
>>> ...                        libelf: [ on  ]
>>> ...                       libnuma: [ on  ]
>>> ...                       libperl: [ on  ]
>>> ...                     libpython: [ on  ]
>>> ...                      libslang: [ on  ]
>>> ...                     libunwind: [ on  ]
>>> ...            libdw-dwarf-unwind: [ on  ]
>>> ...                          zlib: [ on  ]
>>> ...                          lzma: [ on  ]
>>> ...                           bpf: [ OFF ]
>>>
>>>
>>> Doesn't work as well :-\
>>>
>>> Looking at the following patches...
>>>
>>> - Arnaldo