From: Alan Maguire <alan.maguire@oracle.com>
To: Yonghong Song <yhs@fb.com>
Cc: Alan Maguire <alan.maguire@oracle.com>,
ast@kernel.org, daniel@iogearbox.net, bpf@vger.kernel.org,
joe@perches.com, linux@rasmusvillemoes.dk,
arnaldo.melo@gmail.com, kafai@fb.com, songliubraving@fb.com,
andriin@fb.com, john.fastabend@gmail.com, kpsingh@chromium.org,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [PATCH v2 bpf-next 6/7] bpf: add support for %pT format specifier for bpf_trace_printk() helper
Date: Mon, 18 May 2020 10:10:44 +0100 (BST) [thread overview]
Message-ID: <alpine.LRH.2.21.2005181000520.893@localhost> (raw)
In-Reply-To: <040b71a1-9bbf-9a55-6f1a-e7b8c36f8c6e@fb.com>
On Wed, 13 May 2020, Yonghong Song wrote:
>
> > + while (isbtffmt(fmt[i]))
> > + i++;
>
> The pointer passed to the helper may not be valid pointer. I think you
> need to do a probe_read_kernel() here. Do an atomic memory allocation
> here should be okay as this is mostly for debugging only.
>
Are there other examples of doing allocations in program execution
context? I'd hate to be the first to introduce one if not. I was hoping
I could get away with some per-CPU scratch space. Most data structures
will fit within a small per-CPU buffer, but if multiple copies
are required, performance isn't the key concern. It will make traversing
the buffer during display a bit more complex but I think avoiding
allocation might make that complexity worth it. The other thought I had
was we could carry out an allocation associated with the attach,
but that's messy as it's possible run-time might determine the type for
display (and thus the amount of the buffer we need to copy safely).
Great news about LLVM support for __builtin_btf_type_id()!
Thanks!
Alan
next prev parent reply other threads:[~2020-05-18 9:11 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-12 5:56 [PATCH v2 bpf-next 0/7] bpf, printk: add BTF-based type printing Alan Maguire
2020-05-12 5:56 ` [PATCH v2 bpf-next 1/7] bpf: provide function to get vmlinux BTF information Alan Maguire
2020-05-12 5:56 ` [PATCH v2 bpf-next 2/7] bpf: move to generic BTF show support, apply it to seq files/strings Alan Maguire
2020-05-13 23:04 ` Yonghong Song
2020-05-18 9:46 ` Alan Maguire
2020-05-19 6:21 ` Yonghong Song
2020-05-12 5:56 ` [PATCH v2 bpf-next 3/7] checkpatch: add new BTF pointer format specifier Alan Maguire
2020-05-12 5:56 ` [PATCH v2 bpf-next 4/7] printk: add type-printing %pT format specifier which uses BTF Alan Maguire
2020-05-13 23:05 ` Joe Perches
2020-05-13 23:07 ` Alexei Starovoitov
2020-05-13 23:22 ` Joe Perches
2020-05-14 23:43 ` Joe Perches
2020-05-15 0:09 ` Alexei Starovoitov
2020-05-15 0:21 ` Joe Perches
2020-05-14 0:45 ` Yonghong Song
2020-05-14 22:37 ` Alan Maguire
2020-05-15 0:39 ` Yonghong Song
2020-05-12 5:56 ` [PATCH v2 bpf-next 5/7] printk: extend test_printf to test %pT BTF-based format specifier Alan Maguire
2020-05-12 5:56 ` [PATCH v2 bpf-next 6/7] bpf: add support for %pT format specifier for bpf_trace_printk() helper Alan Maguire
2020-05-14 0:53 ` Yonghong Song
2020-05-18 9:10 ` Alan Maguire [this message]
2020-05-18 14:47 ` Yonghong Song
2020-05-12 5:56 ` [PATCH v2 bpf-next 7/7] bpf: add tests for %pT format specifier Alan Maguire
2020-05-15 0:21 ` Andrii Nakryiko
2020-05-13 22:24 ` [PATCH v2 bpf-next 0/7] bpf, printk: add BTF-based type printing Alexei Starovoitov
2020-05-13 22:48 ` Joe Perches
2020-05-13 22:50 ` Alexei Starovoitov
2020-05-13 23:23 ` Joe Perches
2020-05-14 17:46 ` Alan Maguire
2020-05-15 18:59 ` Yonghong Song
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