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References: <20220703130924.57240-1-dlan@gentoo.org> <YsKAZUJRo5cjtZ3n@infradead.org>
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From:   Andrii Nakryiko <andrii.nakryiko@gmail.com>
Date:   Tue, 5 Jul 2022 22:00:42 -0700
Message-ID: <CAEf4BzbCswMd6KU7f9SEU6xHBBPu_rTL5f+KE0OkYj63e-h-bA@mail.gmail.com>
Subject: Re: [PATCH] RISC-V/bpf: Enable bpf_probe_read{, str}()
To:     Christoph Hellwig <hch@infradead.org>,
        Alan Maguire <alan.maguire@oracle.com>
Cc:     Yixun Lan <dlan@gentoo.org>, Palmer Dabbelt <palmer@dabbelt.com>,
        linux-riscv@lists.infradead.org,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>
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On Sun, Jul 3, 2022 at 10:53 PM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Sun, Jul 03, 2022 at 09:09:24PM +0800, Yixun Lan wrote:
> > Enable this option to fix a bcc error in RISC-V platform
> >
> > And, the error shows as follows:
>
> These should not be enabled on new platforms.  Use the proper helpers
> to probe kernel vs user pointers instead.

riscv existed as of [0], so I'd argue it is a proper bug fix, as
corresponding select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE should
have been added back then.

But I also agree that BCC tools should be updated to use proper
bpf_probe_read_{kernel,user}[_str()] helpers, please contribute such
fixes to BCC tools and BCC itself as well. Cc'ed Alan as his ksnoop in
libbpf-tools seems to be using bpf_probe_read() as well and needs to
be fixed.

  [0] 0ebeea8ca8a4 ("bpf: Restrict bpf_probe_read{, str}() only to
archs where they work")