[External] Re: [PATCH bpf-next v2 1/9] bpf: tracing: add support to record and check the accessed args

Andrii Nakryiko andrii.nakryiko at gmail.com
Sat Mar 30 19:34:33 PDT 2024


On Sat, Mar 30, 2024 at 10:52 AM Jiri Olsa <olsajiri at gmail.com> wrote:
>
> On Sat, Mar 30, 2024 at 08:27:55AM -0400, Steven Rostedt wrote:
> > On Fri, 29 Mar 2024 16:28:33 -0700
> > Andrii Nakryiko <andrii.nakryiko at gmail.com> wrote:
> >
> > > I thought I'll just ask instead of digging through code, sorry for
> > > being lazy :) Is there any way to pass pt_regs/ftrace_regs captured
> > > before function execution to a return probe (fexit/kretprobe)? I.e.,
> > > how hard is it to pass input function arguments to a kretprobe? That's
> > > the biggest advantage of fexit over kretprobe, and if we can make
> > > these original pt_regs/ftrace_regs available to kretprobe, then
> > > multi-kretprobe will effectively be this multi-fexit.
> >
> > This should be possible with the updates that Masami is doing with the
> > fgraph code.
>
> yes, I have bpf kprobe-multi link support for that [0] (it's on top of
> Masami's fprobe-over-fgraph changes) we discussed that in [1]

Sorry, I forgot the regs/args part, mostly remembering we discussed
session cookie ideas. Thanks for reminder!

>
> jirka
>
> [0] https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git/log/?h=bpf/session_data
> [1] https://lore.kernel.org/bpf/20240228090242.4040210-1-jolsa@kernel.org/

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In-Reply-To: <ZghRXtc8ZiTOKMR3 at krava>
From: Andrii Nakryiko <andrii.nakryiko at gmail.com>
Date: Sat, 30 Mar 2024 19:34:33 -0700
Message-ID: <CAEf4BzbOAwLZ9=MQo-W5oHxTA7nM5ERRp0Q=huC8b+Y1Ww at mail.gmail.com>
Subject: Re: [External] Re: [PATCH bpf-next v2 1/9] bpf: tracing: add support
 to record and check the accessed args
To: Jiri Olsa <olsajiri at gmail.com>
Cc: Steven Rostedt <rostedt at goodmis.org>, =TF-8?B?5qKm6b6Z6JGj?=ongmenglong.8 at bytedance.com>, 
	Alexei Starovoitov <alexei.starovoitov at gmail.com>, Andrii Nakryiko <andrii at kernel.org>, 
	Alexei Starovoitov <ast at kernel.org>, Daniel Borkmann <daniel at iogearbox.net>, 
	Martin KaFai Lau <martin.lau at linux.dev>, Eddy Z <eddyz87 at gmail.com>, Song Liu <song at kernel.org>, 
	Yonghong Song <yonghong.song at linux.dev>, John Fastabend <john.fastabend at gmail.com>, 
	KP Singh <kpsingh at kernel.org>, Stanislav Fomichev <sdf at google.com>, Hao Luo <haoluo at google.com>, 
	Alexander Gordeev <agordeev at linux.ibm.com>, Christian Borntraeger <borntraeger at linux.ibm.com>, 
	Sven Schnelle <svens at linux.ibm.com>, "David S. Miller" <davem at davemloft.net>, 
	David Ahern <dsahern at kernel.org>, Dave Hansen <dave.hansen at linux.intel.com>, 
	X86 ML <x86 at kernel.org>, Mathieu Desnoyers <mathieu.desnoyers at efficios.com>, 
	Quentin Monnet <quentin at isovalent.com>, bpf <bpf at vger.kernel.org>, 
	linux-arm-kernel <linux-arm-kernel at lists.infradead.org>, LKML <linux-kernel at vger.kernel.org>, 
	linux-riscv <linux-riscv at lists.infradead.org>, linux-s390 <linux-s390 at vger.kernel.org>, 
	Network Development <netdev at vger.kernel.org>, linux-trace-kernel at vger.kernel.org, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest at vger.kernel.org>, linux-stm32 at st-md-mailman.stormreply.com
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On Sat, Mar 30, 2024 at 10:52 AM Jiri Olsa <olsajiri at gmail.com> wrote:
>
> On Sat, Mar 30, 2024 at 08:27:55AM -0400, Steven Rostedt wrote:
> > On Fri, 29 Mar 2024 16:28:33 -0700
> > Andrii Nakryiko <andrii.nakryiko at gmail.com> wrote:
> >
> > > I thought I'll just ask instead of digging through code, sorry for
> > > being lazy :) Is there any way to pass pt_regs/ftrace_regs captured
> > > before function execution to a return probe (fexit/kretprobe)? I.e.,
> > > how hard is it to pass input function arguments to a kretprobe? That's
> > > the biggest advantage of fexit over kretprobe, and if we can make
> > > these original pt_regs/ftrace_regs available to kretprobe, then
> > > multi-kretprobe will effectively be this multi-fexit.
> >
> > This should be possible with the updates that Masami is doing with the
> > fgraph code.
>
> yes, I have bpf kprobe-multi link support for that [0] (it's on top of
> Masami's fprobe-over-fgraph changes) we discussed that in [1]

Sorry, I forgot the regs/args part, mostly remembering we discussed
session cookie ideas. Thanks for reminder!

>
> jirka
>
> [0] https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git/log/?h=bpf/session_data
> [1] https://lore.kernel.org/bpf/20240228090242.4040210-1-jolsa@kernel.org/

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From: Andrii Nakryiko <andrii.nakryiko at gmail.com>
Date: Sat, 30 Mar 2024 19:34:33 -0700
Message-ID: <CAEf4BzbOAwLZ9=MQo-W5oHxTA7nM5ERRp0Q=huC8b+Y1Ww at mail.gmail.com>
Subject: Re: [External] Re: [PATCH bpf-next v2 1/9] bpf: tracing: add support
 to record and check the accessed args
To: Jiri Olsa <olsajiri at gmail.com>
Cc: Steven Rostedt <rostedt at goodmis.org>, =TF-8?B?5qKm6b6Z6JGj?=ongmenglong.8 at bytedance.com>, 
	Alexei Starovoitov <alexei.starovoitov at gmail.com>, Andrii Nakryiko <andrii at kernel.org>, 
	Alexei Starovoitov <ast at kernel.org>, Daniel Borkmann <daniel at iogearbox.net>, 
	Martin KaFai Lau <martin.lau at linux.dev>, Eddy Z <eddyz87 at gmail.com>, Song Liu <song at kernel.org>, 
	Yonghong Song <yonghong.song at linux.dev>, John Fastabend <john.fastabend at gmail.com>, 
	KP Singh <kpsingh at kernel.org>, Stanislav Fomichev <sdf at google.com>, Hao Luo <haoluo at google.com>, 
	Alexander Gordeev <agordeev at linux.ibm.com>, Christian Borntraeger <borntraeger at linux.ibm.com>, 
	Sven Schnelle <svens at linux.ibm.com>, "David S. Miller" <davem at davemloft.net>, 
	David Ahern <dsahern at kernel.org>, Dave Hansen <dave.hansen at linux.intel.com>, 
	X86 ML <x86 at kernel.org>, Mathieu Desnoyers <mathieu.desnoyers at efficios.com>, 
	Quentin Monnet <quentin at isovalent.com>, bpf <bpf at vger.kernel.org>, 
	linux-arm-kernel <linux-arm-kernel at lists.infradead.org>, LKML <linux-kernel at vger.kernel.org>, 
	linux-riscv <linux-riscv at lists.infradead.org>, linux-s390 <linux-s390 at vger.kernel.org>, 
	Network Development <netdev at vger.kernel.org>, linux-trace-kernel at vger.kernel.org, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest at vger.kernel.org>, linux-stm32 at st-md-mailman.stormreply.com
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On Sat, Mar 30, 2024 at 10:52 AM Jiri Olsa <olsajiri at gmail.com> wrote:
>
> On Sat, Mar 30, 2024 at 08:27:55AM -0400, Steven Rostedt wrote:
> > On Fri, 29 Mar 2024 16:28:33 -0700
> > Andrii Nakryiko <andrii.nakryiko at gmail.com> wrote:
> >
> > > I thought I'll just ask instead of digging through code, sorry for
> > > being lazy :) Is there any way to pass pt_regs/ftrace_regs captured
> > > before function execution to a return probe (fexit/kretprobe)? I.e.,
> > > how hard is it to pass input function arguments to a kretprobe? That's
> > > the biggest advantage of fexit over kretprobe, and if we can make
> > > these original pt_regs/ftrace_regs available to kretprobe, then
> > > multi-kretprobe will effectively be this multi-fexit.
> >
> > This should be possible with the updates that Masami is doing with the
> > fgraph code.
>
> yes, I have bpf kprobe-multi link support for that [0] (it's on top of
> Masami's fprobe-over-fgraph changes) we discussed that in [1]

Sorry, I forgot the regs/args part, mostly remembering we discussed
session cookie ideas. Thanks for reminder!

>
> jirka
>
> [0] https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git/log/?h=bpf/session_data
> [1] https://lore.kernel.org/bpf/20240228090242.4040210-1-jolsa@kernel.org/




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