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

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

On 2015/6/30 3:41, Arnaldo Carvalho de Melo wrote:
> Em Mon, Jun 29, 2015 at 04:21:51PM -0300, Arnaldo Carvalho de Melo escreveu:
>> Em Fri, Jun 26, 2015 at 02:15:07PM +0000, Wang Nan escreveu:
>>> In this patch, eBPF API is checked by compiling a c source file which
>>> uses fields in bpf_attr which will be used by libbpf.
>>>
>>> Signed-off-by: Wang Nan <wangnan0@huawei.com>
>>> Acked-by: Alexei Starovoitov <ast@plumgrid.com>
>> So, I just applied this and after trying:
>>
>> [acme@felicio linux]$ rm -rf /tmp/build/perf ; mkdir -p /tmp/build/perf
>> ; make O=/tmp/build/perf -C tools/perf  install-bin
>> 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 ]
>>
>>    MKDIR    /tmp/build/perf/util/
>>    CC       /tmp/build/perf/util/abspath.o
>>
>> --------------------------------------------------------
>>
>> 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'.

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'
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:

# 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