From: Masami Hiramatsu <mhiramat@kernel•org>
To: Jiri Olsa <jolsa@redhat•com>
Cc: Alexei Starovoitov <ast@kernel•org>,
Daniel Borkmann <daniel@iogearbox•net>,
Andrii Nakryiko <andrii@kernel•org>,
netdev@vger•kernel.org, bpf@vger•kernel.org,
lkml <linux-kernel@vger•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@chromium•org>,
Steven Rostedt <rostedt@goodmis•org>,
"Naveen N . Rao" <naveen.n.rao@linux•ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@intel•com>,
"David S . Miller" <davem@davemloft•net>
Subject: Re: [PATCH v5 2/9] fprobe: Add ftrace based probe APIs
Date: Wed, 26 Jan 2022 11:50:22 +0900 [thread overview]
Message-ID: <20220126115022.fda21a3face4e97684f5bab9@kernel.org> (raw)
In-Reply-To: <YfA9aC5quQNc89Hc@krava>
On Tue, 25 Jan 2022 19:11:52 +0100
Jiri Olsa <jolsa@redhat•com> wrote:
> On Tue, Jan 25, 2022 at 05:41:24PM +0100, Jiri Olsa wrote:
> > On Tue, Jan 25, 2022 at 09:11:57PM +0900, Masami Hiramatsu wrote:
> >
> > SNIP
> >
> > > +
> > > +/* Convert ftrace location address from symbols */
> > > +static int convert_func_addresses(struct fprobe *fp)
> > > +{
> > > + unsigned long addr, size;
> > > + unsigned int i;
> > > +
> > > + /* Convert symbols to symbol address */
> > > + if (fp->syms) {
> > > + fp->addrs = kcalloc(fp->nentry, sizeof(*fp->addrs), GFP_KERNEL);
> > > + if (!fp->addrs)
> > > + return -ENOMEM;
> > > +
> > > + for (i = 0; i < fp->nentry; i++) {
> > > + fp->addrs[i] = kallsyms_lookup_name(fp->syms[i]);
> > > + if (!fp->addrs[i]) /* Maybe wrong symbol */
> > > + goto error;
> > > + }
> > > + }
> > > +
> > > + /* Convert symbol address to ftrace location. */
> > > + for (i = 0; i < fp->nentry; i++) {
> > > + if (!kallsyms_lookup_size_offset(fp->addrs[i], &size, NULL))
> > > + size = MCOUNT_INSN_SIZE;
> > > + addr = ftrace_location_range(fp->addrs[i], fp->addrs[i] + size);
> >
> > you need to substract 1 from 'end' in here, as explained in
> > __within_notrace_func comment:
> >
> > /*
> > * Since ftrace_location_range() does inclusive range check, we need
> > * to subtract 1 byte from the end address.
> > */
> >
> > like in the patch below
Good catch, I missed that point.
> > also this convert is for archs where address from kallsyms does not match
> > the real attach addresss, like for arm you mentioned earlier, right?
Yes, that's right.
> >
> > could we have that arch specific, so we don't have extra heavy search
> > loop for archs that do not need it?
Hmm, is that so heavy? Even though, this kind of convertion is better
to be implemented in the arch-specific ftrace. They may know the
best way to do, because the offset is fixed for each arch.
>
> one more question..
>
> I'm adding support for user to pass function symbols to bpf fprobe link
> and I thought I'd pass symbols array to register_fprobe, but I'd need to
> copy the whole array of strings from user space first, which could take
> lot of memory considering attachment of 10k+ functions
>
> so I'm thinking better way is to resolve symbols already in bpf fprobe
> link code and pass just addresses to register_fprobe
That is OK. Fprobe accepts either ::syms or ::addrs.
>
> I assume you want to keep symbol interface, right? could we have some
> flag ensuring the conversion code is skipped, so we don't go through
> it twice?
Yeah, we still have many unused bits in fprobe::flags. :)
Thank you,
> in any case I need addresses before I call register_fprobe, because
> of the bpf cookies setup
>
> thanks,
> jirka
>
--
Masami Hiramatsu <mhiramat@kernel•org>
next prev parent reply other threads:[~2022-01-26 2:50 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-25 12:11 [PATCH v5 0/9] fprobe: Introduce fprobe function entry/exit probe Masami Hiramatsu
2022-01-25 12:11 ` [PATCH v5 1/9] ftrace: Add ftrace_set_filter_ips function Masami Hiramatsu
2022-01-25 16:06 ` Steven Rostedt
2022-01-25 16:46 ` Jiri Olsa
2022-01-28 2:05 ` Masami Hiramatsu
2022-01-28 9:37 ` Jiri Olsa
2022-01-25 12:11 ` [PATCH v5 2/9] fprobe: Add ftrace based probe APIs Masami Hiramatsu
2022-01-25 16:21 ` Steven Rostedt
2022-01-26 9:06 ` Masami Hiramatsu
2022-01-25 16:41 ` Jiri Olsa
2022-01-25 18:11 ` Jiri Olsa
2022-01-26 2:50 ` Masami Hiramatsu [this message]
2022-01-26 15:59 ` Masami Hiramatsu
2022-01-26 18:39 ` Jiri Olsa
2022-01-25 12:12 ` [PATCH v5 3/9] rethook: Add a generic return hook Masami Hiramatsu
2022-01-25 16:46 ` Steven Rostedt
2022-01-26 0:10 ` Masami Hiramatsu
2022-01-26 5:29 ` Masami Hiramatsu
2022-01-25 12:12 ` [PATCH v5 4/9] rethook: x86: Add rethook x86 implementation Masami Hiramatsu
2022-01-25 12:12 ` [PATCH v5 5/9] ARM: rethook: Add rethook arm implementation Masami Hiramatsu
2022-01-25 12:12 ` [PATCH v5 6/9] arm64: rethook: Add arm64 rethook implementation Masami Hiramatsu
2022-01-25 12:12 ` [PATCH v5 7/9] fprobe: Add exit_handler support Masami Hiramatsu
2022-01-25 17:08 ` Steven Rostedt
2022-01-25 12:13 ` [PATCH v5 8/9] fprobe: Add sample program for fprobe Masami Hiramatsu
2022-01-25 12:13 ` [PATCH v5 9/9] docs: fprobe: Add fprobe description to ftrace-use.rst Masami Hiramatsu
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