From: Yonghong Song <yhs@fb.com>
To: Andrii Nakryiko <andriin@fb.com>, <bpf@vger.kernel.org>,
<netdev@vger.kernel.org>, <ast@fb.com>, <daniel@iogearbox.net>,
<ethercflow@gmail.com>
Cc: <andrii.nakryiko@gmail.com>, <kernel-team@fb.com>
Subject: Re: [PATCH bpf-next 1/3] bpf: reliably preserve btf_trace_xxx types
Date: Mon, 2 Mar 2020 08:35:17 -0800 [thread overview]
Message-ID: <eeec59cd-f564-23c7-9fd3-ef460ef162da@fb.com> (raw)
In-Reply-To: <20200301081045.3491005-2-andriin@fb.com>
On 3/1/20 12:10 AM, Andrii Nakryiko wrote:
> btf_trace_xxx types, crucial for tp_btf BPF programs (raw tracepoint with
> verifier-checked direct memory access), have to be preserved in kernel BTF to
> allow verifier do its job and enforce type/memory safety. It was reported
> ([0]) that for kernels built with Clang current type-casting approach doesn't
> preserve these types.
>
> This patch fixes it by declaring an anonymous union for each registered
> tracepoint, capturing both struct bpf_raw_event_map information, as well as
> recording btf_trace_##call type reliably. Structurally, it's still the same
> content as for a plain struct bpf_raw_event_map, so no other changes are
> necessary.
>
> [0] https://github.com/iovisor/bcc/issues/2770#issuecomment-591007692
>
> Fixes: e8c423fb31fa ("bpf: Add typecast to raw_tracepoints to help BTF generation")
> Reported-by: Wenbo Zhang <ethercflow@gmail.com>
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
clang seems doing a little bit optimization here...
The change looks good. It is hard to have code to preserve the types in
the header. union seems an acceptable way.
Acked-by: Yonghong Song <yhs@fb.com>
> ---
> include/trace/bpf_probe.h | 18 +++++++++++-------
> 1 file changed, 11 insertions(+), 7 deletions(-)
>
> diff --git a/include/trace/bpf_probe.h b/include/trace/bpf_probe.h
> index b04c29270973..1ce3be63add1 100644
> --- a/include/trace/bpf_probe.h
> +++ b/include/trace/bpf_probe.h
> @@ -75,13 +75,17 @@ static inline void bpf_test_probe_##call(void) \
> check_trace_callback_type_##call(__bpf_trace_##template); \
> } \
> typedef void (*btf_trace_##call)(void *__data, proto); \
> -static struct bpf_raw_event_map __used \
> - __attribute__((section("__bpf_raw_tp_map"))) \
> -__bpf_trace_tp_map_##call = { \
> - .tp = &__tracepoint_##call, \
> - .bpf_func = (void *)(btf_trace_##call)__bpf_trace_##template, \
> - .num_args = COUNT_ARGS(args), \
> - .writable_size = size, \
> +static union { \
> + struct bpf_raw_event_map event; \
> + btf_trace_##call handler; \
> +} __bpf_trace_tp_map_##call __used \
> +__attribute__((section("__bpf_raw_tp_map"))) = { \
> + .event = { \
> + .tp = &__tracepoint_##call, \
> + .bpf_func = __bpf_trace_##template, \
> + .num_args = COUNT_ARGS(args), \
> + .writable_size = size, \
> + }, \
> };
>
> #define FIRST(x, ...) x
>
next prev parent reply other threads:[~2020-03-02 16:35 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-01 8:10 [PATCH bpf-next 0/3] Improve raw tracepoint BTF types preservation Andrii Nakryiko
2020-03-01 8:10 ` [PATCH bpf-next 1/3] bpf: reliably preserve btf_trace_xxx types Andrii Nakryiko
2020-03-02 16:35 ` Yonghong Song [this message]
2020-03-01 8:10 ` [PATCH bpf-next 2/3] bpf: generate directly-usable raw_tp_##call structs for raw tracepoints Andrii Nakryiko
2020-03-02 16:36 ` Yonghong Song
2020-03-01 8:10 ` [PATCH bpf-next 3/3] tools/runqslower: simplify BPF code by using raw_tp_xxx structs Andrii Nakryiko
2020-03-02 16:36 ` Yonghong Song
2020-03-03 0:59 ` [PATCH bpf-next 0/3] Improve raw tracepoint BTF types preservation Alexei Starovoitov
2020-03-03 4:10 ` Andrii Nakryiko
2020-03-03 4:59 ` Andrii Nakryiko
2020-04-21 21:49 ` Andrii Nakryiko
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