Re: [PATCH bpf-next v3 4/6] libbpf: Unify memory address casting operation style

[Pu Lehui]

On 2022/7/9 6:30, Andrii Nakryiko wrote:
> On Thu, Jul 7, 2022 at 5:23 AM Pu Lehui <pulehui@xxxxxxxxxx> wrote:
> > On 2022/6/4 5:03, Andrii Nakryiko wrote:
> > > On Mon, May 30, 2022 at 2:03 PM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
> > > > On 5/30/22 11:28 AM, Pu Lehui wrote:
> > > > > The members of bpf_prog_info, which are line_info, jited_line_info,
> > > > > jited_ksyms and jited_func_lens, store u64 address pointed to the
> > > > > corresponding memory regions. Memory addresses are conceptually
> > > > > unsigned, (unsigned long) casting makes more sense, so let's make
> > > > > a change for conceptual uniformity.
> > > > >
> > > > > Signed-off-by: Pu Lehui <pulehui@xxxxxxxxxx>
> > > > > ---
> > > > >     tools/lib/bpf/bpf_prog_linfo.c | 9 +++++----
> > > > >     1 file changed, 5 insertions(+), 4 deletions(-)
> > > > >
> > > > > diff --git a/tools/lib/bpf/bpf_prog_linfo.c b/tools/lib/bpf/bpf_prog_linfo.c
> > > > > index 5c503096ef43..7beb060d0671 100644
> > > > > --- a/tools/lib/bpf/bpf_prog_linfo.c
> > > > > +++ b/tools/lib/bpf/bpf_prog_linfo.c
> > > > > @@ -127,7 +127,8 @@ struct bpf_prog_linfo *bpf_prog_linfo__new(const struct bpf_prog_info *info)
> > > > >         prog_linfo->raw_linfo = malloc(data_sz);
> > > > >         if (!prog_linfo->raw_linfo)
> > > > >                 goto err_free;
> > > > > -     memcpy(prog_linfo->raw_linfo, (void *)(long)info->line_info, data_sz);
> > > > > +     memcpy(prog_linfo->raw_linfo, (void *)(unsigned long)info->line_info,
> > > > > +            data_sz);
> > > >
> > > > Took in patch 1-3, lgtm, thanks! My question around the cleanups in patch 4-6 ...
> > > > there are various other such cases e.g. in libbpf, perhaps makes sense to clean all
> > > > of them up at once and not just the 4 locations in here.
> > >
> > > if (void *)(long) pattern is wrong, then I guess the best replacement
> > > should be (void *)(uintptr_t) ?
> >
> > I also think that (void *)(uintptr_t) would be the best replacement. I
> > applied the changes to kernel/bpf and samples/bpf, and it worked fine.
> > But in selftests/bpf, the following similar error occur at compile time:
> >
> > progs/test_cls_redirect.c:504:11: error: cast to 'uint8_t *' (aka
> > 'unsigned char *') from smaller integer type 'uintptr_t' (aka 'unsigned
> > int') [-Werror,-Wint-to-pointer-cast]
> >          .head = (uint8_t *)(uintptr_t)skb->data,
>
> this is BPF-side code so using system's uintptr_t definition won't
> work correctly here. Just do (unsigned long) instead?

It is fine by me, and for this cleanup

> > I take clang to compile with the front and back end separation, like
> > samples/bpf, and it works. It seems that the all-in-one clang has
> > problems handling the uintptr_t.
> >
> > > > Thanks,
> > > > Daniel
> > > .
> .