Re: [PATCH 00/10] bpf samples: Uses libbpf in tools/lib to do BPF operations

[Daniel Wagner <daniel.wagner@bmw-carit.de>]

On 12/17/2015 08:03 AM, Daniel Wagner wrote:
> On 12/17/2015 07:51 AM, Wangnan (F) wrote:
>> On 2015/12/17 14:38, Daniel Wagner wrote:
>>> On 12/17/2015 06:23 AM, Wang Nan wrote:
>>>> Since we already have libbpf in tools/lib, we don't need to maintain
>>>> another bpf loader and operations library in samples/bpf.
>>>>
>>>> In patchset:
>>>>
>>>>   Patch 1/10 - 7/10 improves libbpf, add missing features to support
>>>>   samples,
>>>>
>>>>   Patch 8/10 adds utils.[ch], which creates similar API like old
>>>>   bpf_load.c and libbpf.c.
>>>>
>>>>   Patch 9/10 replace all sampels to use API provides by utils.[ch] and
>>>>   libbpf.
>>>>
>>>>   Patch 10/10 removes unneeded files.
>>> Which tree did you use for your patches? I tried to apply them against
>>> mainline and net-next which didn't really work out.
>>
>> These patches based on Arnaldo's 'perf/core' because of those libbpf
>> changes.
> 
> Okay, I'll try with this one.

I applied those patches on top of

5c560cfcf1c0 ("tools subcmd: Rename subcmd header include guards")

Patch number 2 didn't apply cleanly. After fixing this manually 
I was able to continue to the build step:

$ make samples/bpf/
  CHK     include/config/kernel.release
  CHK     include/generated/uapi/linux/version.h
  CHK     include/generated/utsrelease.h
  CHK     include/generated/bounds.h
  CHK     include/generated/timeconst.h
  CHK     include/generated/asm-offsets.h
  CALL    scripts/checksyscalls.sh
make -C /home/wagi/src/linux/tools/lib/bpf O=/home/wagi/src/linux/samples/bpf/libbpf CFLAGS= LDFLAGS= V=1 /home/wagi/src/linux/samples/bpf/libbpf/libbpf.a
No libelf found
Makefile:203: recipe for target 'elfdep' failed
make[2]: *** [elfdep] Error 255
samples/bpf/Makefile:10: recipe for target 'samples/bpf/libbpf/libbpf.a' failed
make[1]: *** [samples/bpf/libbpf/libbpf.a] Error 2
Makefile:1550: recipe for target 'samples/bpf/' failed
make: *** [samples/bpf/] Error 2


Executing the above command line by myself in order 
to figure out what's going on ended in this mess:


$ make -C /home/wagi/src/linux/tools/lib/bpf O=/home/wagi/src/linux/samples/bpf/libbpf CFLAGS= LDFLAGS= V=1 /home/wagi/src/linux/samples/bpf/libbpf/libbpf.a
make: Entering directory '/home/wagi/src/linux/tools/lib/bpf'

Auto-detecting system features:
...                        libelf: [ on  ]
...                           bpf: [ on  ]

[...]

samples/bpf/fds_example.c: In function ‘bpf_do_map’:
samples/bpf/fds_example.c:78:9: warning: implicit declaration of function ‘bpf_pin_object’ [-Wimplicit-function-declaration]
   ret = bpf_pin_object(fd, file);
         ^
samples/bpf/fds_example.c:82:8: warning: implicit declaration of function ‘bpf_get_pinned_object’ [-Wimplicit-function-declaration]
   fd = bpf_get_pinned_object(file);
        ^
  gcc -Lsamples/bpf/libbpf -o samples/bpf/fds_example samples/bpf/utils.o samples/bpf/fds_example.o -lelf -lbpf 
samples/bpf/fds_example.o: In function `main':
fds_example.c:(.text.startup+0x20e): undefined reference to `bpf_pin_object'
fds_example.c:(.text.startup+0x2b0): undefined reference to `bpf_pin_object'
fds_example.c:(.text.startup+0x2f3): undefined reference to `bpf_get_pinned_object'
fds_example.c:(.text.startup+0x344): undefined reference to `bpf_get_pinned_object'
collect2: error: ld returned 1 exit status
scripts/Makefile.host:100: recipe for target 'samples/bpf/fds_example' failed
make[1]: *** [samples/bpf/fds_example] Error 1
Makefile:1550: recipe for target 'samples/bpf/' failed
make: *** [samples/bpf/] Error 2
[wagi@handman linux (bpf-test)]$ make samples/bpf/
  CHK     include/config/kernel.release
  CHK     include/generated/uapi/linux/version.h
  CHK     include/generated/utsrelease.h
  CHK     include/generated/bounds.h
  CHK     include/generated/timeconst.h
  CHK     include/generated/asm-offsets.h
  CALL    scripts/checksyscalls.sh
  HOSTLD  samples/bpf/fds_example
samples/bpf/fds_example.o: In function `main':
fds_example.c:(.text.startup+0x20e): undefined reference to `bpf_pin_object'
fds_example.c:(.text.startup+0x2b0): undefined reference to `bpf_pin_object'
fds_example.c:(.text.startup+0x2f3): undefined reference to `bpf_get_pinned_object'
fds_example.c:(.text.startup+0x344): undefined reference to `bpf_get_pinned_object'
collect2: error: ld returned 1 exit status


What is the canonical why to build the samples? I must doing something
really stupid I guess.


cheers,
daniel