Re: [Buildroot] [autobuild.buildroot.net] Your daily results for 2022-04-14

[Thomas Petazzoni via buildroot <buildroot@buildroot.org>]

On Fri, 15 Apr 2022 17:42:23 +0100
Francis Laniel <flaniel@linux.microsoft.com> wrote:


> >     arch     |             reason             |                             
> >          url
> > -------------+--------------------------------+----------------------------
> > ----------------------------------------------------- xtensa    |      
> > host-pahole-v1.23        |
> > http://autobuild.buildroot.net/results/fa4fb6ca383e058e89ff8796ac9ae68a0b16
> > 81b5 m68k     |       host-pahole-v1.23        |
> > http://autobuild.buildroot.net/results/b584c57a72e4604112f4b12c0c7b21e1a4b4
> > 1dd5 arm      |       host-pahole-v1.23        |
> > http://autobuild.buildroot.net/results/b43be30cb177066d1b49bf4822790ec0ca01
> > 9d03
> > 
> > 
> > Thanks for your contribution to Buildroot!  
> 
> I suspect this problem occurs because Ubuntu 14.04 kernel does not know the 
> problematic symbols.
> Indeed, PERF_COUNT_SW_BPF_OUTPUT was added in :
> a43eec304259 ("bpf: introduce bpf_perf_event_output() helper")
> which was released with kernel 4.4.
> So, can you please give me the uname -r of the host-distro?

I can't because these build issues (or at least the last one) occurs on
Yann Morin's autobuilder, so I've added yann in Cc.

> If my suspicion is good, I already wrote a patch to throw an error if host 
> kernel is under 4.4 while building host-pahole.

This is not going to be the solution. Why does host-pahole depend on
the version of the kernel? Why does it need the NR_bpf symbol?

There is some logic in src/bpf.c to get __NR_bpf if not provided by
kernel headers:

#ifndef __NR_bpf
# if defined(__i386__)
#  define __NR_bpf 357
# elif defined(__x86_64__)
#  define __NR_bpf 321
# elif defined(__aarch64__)
#  define __NR_bpf 280
# elif defined(__sparc__)
#  define __NR_bpf 349
# elif defined(__s390__)
#  define __NR_bpf 351
# elif defined(__arc__)
#  define __NR_bpf 280
# elif defined(__mips__) && defined(_ABIO32)
#  define __NR_bpf 4355
# elif defined(__mips__) && defined(_ABIN32)
#  define __NR_bpf 6319
# elif defined(__mips__) && defined(_ABI64)
#  define __NR_bpf 5315
# else
#  error __NR_bpf not defined. libbpf does not support your arch.
# endif
#endif

but this logic is only partially duplicated in src/skel_internal.h:

#ifndef __NR_bpf
# if defined(__mips__) && defined(_ABIO32)
#  define __NR_bpf 4355
# elif defined(__mips__) && defined(_ABIN32)
#  define __NR_bpf 6319
# elif defined(__mips__) && defined(_ABI64)
#  define __NR_bpf 5315
# endif
#endif

That doesn't make much sense.

Do we need that BPF support in host-pahole in our use-case of host-pahole?

BTW, I'm seeing that we can avoid using the internal libbpf, and
therefore avoid using git submodules:

option(LIBBPF_EMBEDDED "Use the embedded version of libbpf instead of searching it via pkg-config" ON)
if (NOT LIBBPF_EMBEDDED)
        find_package(PkgConfig REQUIRED)
        if(PKGCONFIG_FOUND)
                pkg_check_modules(LIBBPF REQUIRED libbpf>=0.4.0)
        endif()
endif()

So we should definitely do that, and have a separate Buildroot package
for libbpf.

Best regards,

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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