Re: Re: [PATCH] Fix 'libbpf: failed to find BTF info for global/extern symbol' since uninitialized global variables

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Hi Andrii Nakryiko,

> On Fri, Oct 13, 2023 at 6:45=E2=80=AFAM LiuLingze <luiyanbing@xxxxxxxxxxx> =
> wrote:
> >
> > ---
> >  examples/c/usdt.bpf.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/examples/c/usdt.bpf.c b/examples/c/usdt.bpf.c
> > index 49ba506..2612ec1 100644
> > --- a/examples/c/usdt.bpf.c
> > +++ b/examples/c/usdt.bpf.c
> > @@ -5,7 +5,7 @@
> >  #include <bpf/bpf_tracing.h>
> >  #include <bpf/usdt.bpf.h>
> >
> > -pid_t my_pid;
> > +pid_t my_pid =3D 0;
> 
> This is effectively the same, my_pid will be initialized to zero
> anyways. The difference might be due to you using too old Clang
> version that might still be putting my_pid into a special COM section.
> 
> Also "failed to find BTF info for global/extern symbol" is usually due
> to too old Clang that doesn't emit BTF information for global
> variables.
> 
> So either way, can you try upgrading your Clang and see if the problem pers=
> ists?
> 
> >
> >  SEC("usdt/libc.so.6:libc:setjmp")
> >  int BPF_USDT(usdt_auto_attach, void *arg1, int arg2, void *arg3)
> > --
> > 2.37.2
> >
> >
> 

Thank you for your reply.

Yes, I was able to compile on a newer ubuntu with a higher version of clang.

However, on a development module (nVidia Orin AGX) running an older version of ubuntu, it is not possible to use apt to update clang to a new version. Downloading the source code of a higher version of clang for compilation is cumbersome and affects compatibility. So I hope that with the above changes, the project code can be easily compiled and used in earlier versions.

Thanks,
LiuLingze





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