Re: [PATCH 1/1] perf build: Require at least clang 16.0.6 to build BPF skeletons

[James Clark]

On 12/09/2024 15:50, Arnaldo Carvalho de Melo wrote:
> On Thu, Sep 12, 2024 at 03:40:32PM +0100, James Clark wrote:
> > On 11/09/2024 13:24, Arnaldo Carvalho de Melo wrote:
> > > Howard reported problems using perf features that use BPF:
>
> > >     perf $ clang -v
> > >     Debian clang version 15.0.6
> > >     Target: x86_64-pc-linux-gnu
> > >     Thread model: posix
> > >     InstalledDir: /bin
> > >     Found candidate GCC installation: /bin/../lib/gcc/x86_64-linux-gnu/12
> > >     Selected GCC installation: /bin/../lib/gcc/x86_64-linux-gnu/12
> > >     Candidate multilib: .;@m64
> > >     Selected multilib: .;@m64
> > >     perf $ ./perf trace -e write --max-events=1
> > >     libbpf: prog 'sys_enter_rename': BPF program load failed: Permission denied
> > >     libbpf: prog 'sys_enter_rename': -- BEGIN PROG LOAD LOG --
> > >     0: R1=ctx() R10=fp0
> > >
> > > But it works with:
> > >
> > >     perf $ clang -v
> > >     Debian clang version 16.0.6 (15~deb12u1)
> > >     Target: x86_64-pc-linux-gnu
> > >     Thread model: posix
> > >     InstalledDir: /bin
> > >     Found candidate GCC installation: /bin/../lib/gcc/x86_64-linux-gnu/12
> > >     Selected GCC installation: /bin/../lib/gcc/x86_64-linux-gnu/12
> > >     Candidate multilib: .;@m64
> > >     Selected multilib: .;@m64
> > >     perf $ ./perf trace -e write --max-events=1
> > >          0.000 ( 0.009 ms): gmain/1448 write(fd: 4, buf: \1\0\0\0\0\0\0\0, count: 8)                         = 8 (kworker/0:0-eve)
> > >     perf $
> > >
> > > So lets make that the required version, if you happen to have a slightly
> > > older version where this work, please report so that we can adjust the
> > > minimum required version.
>   
> > I wasn't able to reproduce the issue with either of these versions. But I
> > suppose it could be an issue with only 15.0.6.
>
> Interesting, that complicates things, probably the best way then is to
> try to build it, if it fails, mention that 15.0.6 is known to be
> problematic and suggest working versions?
>
> - Arnaldo

I still wasn't able to reproduce it with 15.0.6. And I double checked 
with V=1 that the build was using the right clang. I suppose it could be 
a build configuration issue, or maybe with a different kernel version?

$  uname --kernel-release
6.8.0-76060800daily20240311-generic

$ ../../llvm-project/build/bin/clang -v
clang version 15.0.6 (https://github.com/llvm/llvm-project.git 
088f33605d8a61ff519c580a71b1dd57d16a03f8)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/james/workspace/linux/linux/../../llvm-project/build/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/11
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/12
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/12
Candidate multilib: .;@m64
Selected multilib: .;@m64

$ git log
commit 003265bb6f028d7bcd7cbd92d6ba2b4e26382796 
(perf-tools-next/perf-tools-next)

$ make O=../build/local/ CLANG=../../llvm-project/build/bin/clang -C \
  tools/perf

$ perf trace -e write --max-events=1

     0.000 ( 0.026 ms): gnome-shell/5454 write(fd: 5, buf:
       0x7fffa102d9b0, count: 8)                           = 8