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Message-ID: <918395a6-122c-4fb0-9761-892b8020b95e@linux.dev>
Date: Tue, 1 Apr 2025 20:40:15 +0800
From: Tao Chen <chen.dylane@...ux.dev>
To: Jiri Olsa <olsajiri@...il.com>
Cc: song@...nel.org, ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
martin.lau@...ux.dev, eddyz87@...il.com, yonghong.song@...ux.dev,
john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me,
haoluo@...gle.com, rostedt@...dmis.org, mhiramat@...nel.org,
mathieu.desnoyers@...icios.com, laoar.shao@...il.com, bpf@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 2/2] bpf: Check link_create parameter for
multi_uprobe
在 2025/4/1 19:03, Jiri Olsa 写道:
> On Mon, Mar 31, 2025 at 05:47:45PM +0800, Tao Chen wrote:
>> The target_fd and flags in link_create no used in multi_uprobe
>> , return -EINVAL if they assigned, keep it same as other link
>> attach apis.
>>
>> Fixes: 89ae89f53d20 ("bpf: Add multi uprobe link")
>> Signed-off-by: Tao Chen <chen.dylane@...ux.dev>
>> ---
>> kernel/trace/bpf_trace.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
>> index 2f206a2a2..f7ebf17e3 100644
>> --- a/kernel/trace/bpf_trace.c
>> +++ b/kernel/trace/bpf_trace.c
>> @@ -3385,6 +3385,9 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>> if (sizeof(u64) != sizeof(void *))
>> return -EOPNOTSUPP;
>>
>> + if (attr->link_create.target_fd || attr->link_create.flags)
>> + return -EINVAL;
>
> I think the CI is failing because usdt code does uprobe multi detection
> with target_fd = -1 and it fails and perf-uprobe fallback will fail on
> not having enough file descriptors
>
Hi jiri
As you said, i found it, thanks.
static int probe_uprobe_multi_link(int token_fd)
{
LIBBPF_OPTS(bpf_prog_load_opts, load_opts,
.expected_attach_type = BPF_TRACE_UPROBE_MULTI,
.token_fd = token_fd,
.prog_flags = token_fd ? BPF_F_TOKEN_FD : 0,
);
LIBBPF_OPTS(bpf_link_create_opts, link_opts);
struct bpf_insn insns[] = {
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_EXIT_INSN(),
};
int prog_fd, link_fd, err;
unsigned long offset = 0;
prog_fd = bpf_prog_load(BPF_PROG_TYPE_KPROBE, NULL, "GPL",
insns, ARRAY_SIZE(insns), &load_opts);
if (prog_fd < 0)
return -errno;
/* Creating uprobe in '/' binary should fail with -EBADF. */
link_opts.uprobe_multi.path = "/";
link_opts.uprobe_multi.offsets = &offset;
link_opts.uprobe_multi.cnt = 1;
link_fd = bpf_link_create(prog_fd, -1, BPF_TRACE_UPROBE_MULTI,
&link_opts);
> but I think at this stage we will brake some user apps by introducing
> this check, link ebpf go library, which passes 0
>
So is it ok just check the flags?
> jirka
>
>
>> +
>> if (!is_uprobe_multi(prog))
>> return -EINVAL;
>>
>> --
>> 2.43.0
>>
--
Best Regards
Tao Chen
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