lkml.org 
[lkml]   [2023]   [Jan]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH] libbpf: resolve kernel function name optimization for kprobe
From


On 1/9/23 1:42 AM, menglong8.dong@gmail.com wrote:
> From: Menglong Dong <imagedong@tencent.com>
>
> The function name in kernel may be changed by the compiler. For example,
> the function 'ip_rcv_core' can be compiled to 'ip_rcv_core.isra.0'.
>
> This kind optimization can happen in any kernel function. Therefor, we
> should conside this case.
>
> If we failed to attach kprobe with a '-ENOENT', then we can lookup the
> kallsyms and check if there is a similar function end with '.xxx', and
> retry.

This might produce incorrect result, so this approach won't work
for all .isra.0 cases. When a function name is changed from
<func> to <func>.isra.<num>, it is possible that compiler may have
make some changes to the arguments, e.g., removing one argument,
chaning a semantics of argument, etc. if bpf program still
uses the original function signature, the bpf program may
produce unexpected result.

>
> Signed-off-by: Menglong Dong <imagedong@tencent.com>
> ---
> tools/lib/bpf/libbpf.c | 37 ++++++++++++++++++++++++++++++++++++-
> 1 file changed, 36 insertions(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index a5c67a3c93c5..fdfb1ca34ced 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -10375,12 +10375,30 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
> return libbpf_err_ptr(err);
> }
>
> +struct kprobe_resolve {
> + char pattern[128];
> + char name[128];
> +};
> +
> +static int kprobe_kallsyms_cb(unsigned long long sym_addr, char sym_type,
> + const char *sym_name, void *ctx)
> +{
> + struct kprobe_resolve *res = ctx;
> +
> + if (!glob_match(sym_name, res->pattern))
> + return 0;
> + strcpy(res->name, sym_name);
> + return 1;
> +}
> +
> static int attach_kprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link)
> {
> DECLARE_LIBBPF_OPTS(bpf_kprobe_opts, opts);
> + struct kprobe_resolve res = {};
> unsigned long offset = 0;
> const char *func_name;
> char *func;
> + int err;
> int n;
>
> *link = NULL;
> @@ -10408,8 +10426,25 @@ static int attach_kprobe(const struct bpf_program *prog, long cookie, struct bpf
>
> opts.offset = offset;
> *link = bpf_program__attach_kprobe_opts(prog, func, &opts);
> + err = libbpf_get_error(*link);
> +
> + if (!err || err != -ENOENT)
> + goto out;
> +
> + sprintf(res.pattern, "%s.*", func);
> + if (!libbpf_kallsyms_parse(kprobe_kallsyms_cb, &res))
> + goto out;
> +
> + pr_warn("prog '%s': trying to create %s '%s+0x%zx' perf event instead\n",
> + prog->name, opts.retprobe ? "kretprobe" : "kprobe",
> + res.name, offset);
> +
> + *link = bpf_program__attach_kprobe_opts(prog, res.name, &opts);
> + err = libbpf_get_error(*link);
> +
> +out:
> free(func);
> - return libbpf_get_error(*link);
> + return err;
> }
>
> static int attach_ksyscall(const struct bpf_program *prog, long cookie, struct bpf_link **link)

\
 
 \ /
  Last update: 2023-03-26 23:33    [W:0.068 / U:0.396 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site