On Mon, Oct 16, 2023 at 8:16 PM Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:
> On Sat, Oct 14, 2023 at 4:27 AM LiuLingze <luiyanbing@xxxxxxxxxxx> wrote:
> >
> > Hi Andrii Nakryiko,
> >
> > > On Fri, Oct 13, 2023 at 6:45 AM 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.
>
> Did you verify that specifically adding explicit `= 0` makes it more
> compatible with old compiler or it's just a theory?
Yes, I have compiled usdt successfully on Ubuntu 20.04.6 LTS with clang version 10.0.0-4ubuntu1 by specifically adding explicit `= 0`.
