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From:   Joanne Koong <joannelkoong@gmail.com>
Date:   Fri, 5 Aug 2022 09:29:40 -0700
Message-ID: <CAJnrk1ZHY+ajmMkG-pB_bjWhb0g-HJmeKg6NtP4YC2m8cjvW0Q@mail.gmail.com>
Subject: Re: [PATCH bpf-next v1 3/3] selftests/bpf: tests for using dynptrs to
 parse skb and xdp buffers
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@gmail.com>,
        bpf <bpf@vger.kernel.org>, Andrii Nakryiko <andrii@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Alexei Starovoitov <ast@kernel.org>
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On Thu, Aug 4, 2022 at 11:45 AM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Wed, Aug 3, 2022 at 9:11 AM Joanne Koong <joannelkoong@gmail.com> wrote:
> > >
> > > __builtin_memcpy() is best. When we write just "memcpy()" we still
> > > rely on compiler to actually optimizing that to __builtin_memcpy(),
> > > because there is no memcpy() (we'd get unrecognized extern error if
> > > compiler actually emitted call to memcpy()).
> >
> > Ohh I see, thanks for the explanation!
> >
> > I am going to do some selftests cleanup this week, so I'll change the
> > other usages of memcpy() to __builtin_memcpy() as part of that clean
> > up.
>
> builtin_memcpy might be doing single byte copy when
> alignment is not known which is often the case when
> working with packets.
> If we do this cleanup, let's copy-paste cilium's memcpy
> helper that does 8 byte copy.
> It's much better than builtin_memcpy.
> https://github.com/cilium/cilium/blob/master/bpf/include/bpf/builtins.h

Maybe we should have a separate patchset to changing to use cilium's
other builtins as well (eg memzero, memcmp, memmove); I'll leave the
memcpy() -> __builtin_memcpy() changes to be part of that patchset.