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Rao" , Will Deacon , "David S. Miller" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH v7 3/3] arm64: implement KPROBES_ON_FTRACE Thread-Topic: [PATCH v7 3/3] arm64: implement KPROBES_ON_FTRACE Thread-Index: AQHVuwfioeAAP6kOPkCZLC/0/SnpxKfLukGAgAAB3gCAABLQAA== Date: Thu, 26 Dec 2019 04:25:24 +0000 Message-ID: <20191226121108.0cd1b078@xhacker.debian> References: <20191225172625.69811b3e@xhacker.debian> <20191225173001.6c0e3fb2@xhacker.debian> <20191226115707.902545688aa90b34e2e550b3@kernel.org> <20191226110348.146bb80b@xhacker.debian> In-Reply-To: <20191226110348.146bb80b@xhacker.debian> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [124.74.246.114] x-clientproxiedby: TYAPR01CA0015.jpnprd01.prod.outlook.com (2603:1096:404::27) To BYAPR03MB4773.namprd03.prod.outlook.com (2603:10b6:a03:139::21) authentication-results: spf=none (sender IP is ) smtp.mailfrom=Jisheng.Zhang@synaptics.com; x-ms-exchange-messagesentrepresentingtype: 1 x-mailer: Claws Mail 3.17.4 (GTK+ 2.24.32; x86_64-pc-linux-gnu) x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 13b2c609-2e66-465b-6a56-08d789bba078 x-ms-traffictypediagnostic: BYAPR03MB4582: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:10000; x-forefront-prvs: 02638D901B x-forefront-antispam-report: SFV:NSPM;SFS:(10009020)(136003)(39860400002)(376002)(366004)(396003)(346002)(199004)(189003)(51874003)(7416002)(6506007)(55016002)(9686003)(86362001)(71200400001)(956004)(8936002)(66946007)(478600001)(8676002)(64756008)(1076003)(66476007)(66556008)(81166006)(66446008)(81156014)(2906002)(52116002)(7696005)(4326008)(5660300002)(6916009)(54906003)(16526019)(966005)(316002)(26005)(186003)(39210200001);DIR:OUT;SFP:1101;SCL:1;SRVR:BYAPR03MB4582;H:BYAPR03MB4773.namprd03.prod.outlook.com;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords;A:0;MX:1; received-spf: None (protection.outlook.com: synaptics.com does not designate permitted sender hosts) x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: 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 x-ms-exchange-transport-forked: True Content-Type: text/plain; charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: synaptics.com X-MS-Exchange-CrossTenant-Network-Message-Id: 13b2c609-2e66-465b-6a56-08d789bba078 X-MS-Exchange-CrossTenant-originalarrivaltime: 26 Dec 2019 04:25:24.3278 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 335d1fbc-2124-4173-9863-17e7051a2a0e X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: PLeu9uEDv0WZyzhbuAxBFyvmhQIa1o78hUcORNMVsF7ryOpqZ7omI3/6/XMc/oFkT3VxRNhtSxCBW8soWffvCg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR03MB4582 Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Thu, 26 Dec 2019 03:18:07 +0000 Jisheng Zhang wrote: >=20 >=20 > Hi >=20 > On Thu, 26 Dec 2019 11:57:07 +0900 Masami Hiramatsu wrote: >=20 > > > > Hi Jisheng, > > > > On Wed, 25 Dec 2019 09:44:21 +0000 > > Jisheng Zhang wrote: > > =20 > > > KPROBES_ON_FTRACE avoids much of the overhead with regular kprobes as= it > > > eliminates the need for a trap, as well as the need to emulate or > > > single-step instructions. > > > > > > Tested on berlin arm64 platform. > > > > > > ~ # mount -t debugfs debugfs /sys/kernel/debug/ > > > ~ # cd /sys/kernel/debug/ > > > /sys/kernel/debug # echo 'p _do_fork' > tracing/kprobe_events > > > > > > before the patch: > > > > > > /sys/kernel/debug # cat kprobes/list > > > ffffff801009fe28 k _do_fork+0x0 [DISABLED] > > > > > > after the patch: > > > > > > /sys/kernel/debug # cat kprobes/list > > > ffffff801009ff54 k _do_fork+0x0 [DISABLED][FTRACE] =20 > > > > What happens if user puts a probe on _do_fork+4? > > Is that return -EILSEQ correctly? =20 >=20 > _do_fork+4 can be probed successfully. >=20 > > =20 > > > > > > Signed-off-by: Jisheng Zhang > > > --- > > > .../debug/kprobes-on-ftrace/arch-support.txt | 2 +- > > > arch/arm64/Kconfig | 1 + > > > arch/arm64/include/asm/ftrace.h | 1 + > > > arch/arm64/kernel/probes/Makefile | 1 + > > > arch/arm64/kernel/probes/ftrace.c | 78 +++++++++++++++++= ++ > > > 5 files changed, 82 insertions(+), 1 deletion(-) > > > create mode 100644 arch/arm64/kernel/probes/ftrace.c > > > > > > diff --git a/Documentation/features/debug/kprobes-on-ftrace/arch-supp= ort.txt b/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt > > > index 4fae0464ddff..f9dd9dd91e0c 100644 > > > --- a/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt > > > +++ b/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt > > > @@ -9,7 +9,7 @@ > > > | alpha: | TODO | > > > | arc: | TODO | > > > | arm: | TODO | > > > - | arm64: | TODO | > > > + | arm64: | ok | > > > | c6x: | TODO | > > > | csky: | TODO | > > > | h8300: | TODO | > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > > index b1b4476ddb83..92b9882889ac 100644 > > > --- a/arch/arm64/Kconfig > > > +++ b/arch/arm64/Kconfig > > > @@ -166,6 +166,7 @@ config ARM64 > > > select HAVE_STACKPROTECTOR > > > select HAVE_SYSCALL_TRACEPOINTS > > > select HAVE_KPROBES > > > + select HAVE_KPROBES_ON_FTRACE > > > select HAVE_KRETPROBES > > > select HAVE_GENERIC_VDSO > > > select IOMMU_DMA if IOMMU_SUPPORT > > > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm= /ftrace.h > > > index 91fa4baa1a93..875aeb839654 100644 > > > --- a/arch/arm64/include/asm/ftrace.h > > > +++ b/arch/arm64/include/asm/ftrace.h > > > @@ -20,6 +20,7 @@ > > > > > > /* The BL at the callsite's adjusted rec->ip */ > > > #define MCOUNT_INSN_SIZE AARCH64_INSN_SIZE > > > +#define FTRACE_IP_EXTENSION MCOUNT_INSN_SIZE > > > > > > #define FTRACE_PLT_IDX 0 > > > #define FTRACE_REGS_PLT_IDX 1 > > > diff --git a/arch/arm64/kernel/probes/Makefile b/arch/arm64/kernel/pr= obes/Makefile > > > index 8e4be92e25b1..4020cfc66564 100644 > > > --- a/arch/arm64/kernel/probes/Makefile > > > +++ b/arch/arm64/kernel/probes/Makefile > > > @@ -4,3 +4,4 @@ obj-$(CONFIG_KPROBES) +=3D kprobes.o decode-i= nsn.o \ > > > simulate-insn.o > > > obj-$(CONFIG_UPROBES) +=3D uprobes.o decode-insn.o = \ > > > simulate-insn.o > > > +obj-$(CONFIG_KPROBES_ON_FTRACE) +=3D ftrace.o > > > diff --git a/arch/arm64/kernel/probes/ftrace.c b/arch/arm64/kernel/pr= obes/ftrace.c > > > new file mode 100644 > > > index 000000000000..0643aa2dacdb > > > --- /dev/null > > > +++ b/arch/arm64/kernel/probes/ftrace.c > > > @@ -0,0 +1,78 @@ > > > +// SPDX-License-Identifier: GPL-2.0-or-later > > > +/* > > > + * Dynamic Ftrace based Kprobes Optimization > > > + * > > > + * Copyright (C) Hitachi Ltd., 2012 > > > + * Copyright (C) 2019 Jisheng Zhang > > > + * Synaptics Incorporated > > > + */ > > > + > > > +#include > > > + > > > +/* > > > + * In arm64 FTRACE_WITH_REGS implementation, we patch two nop instru= ctions: > > > + * the lr saver and bl ftrace-entry. Both these instructions are cla= imed > > > + * by ftrace and we should allow probing on either instruction. =20 > > > > No, the 2nd bl ftrace-entry must not be probed. > > The pair of lr-saver and bl ftrace-entry is tightly coupled. You can no= t > > decouple it. =20 >=20 > This is the key. different viewing of this results in different implement= ation. > I'm just wondering why are the two instructions considered as coupled. I = think > here we met similar situation as powerpc: https://lkml.org/lkml/2019/6/18= /646 > the "mflr r0" equals to lr-saver here, branch to _mcount equals to bl ftr= ace-entry > could you please kindly comment more? >=20 > Thanks in advance >=20 hmm, I think I may get some part of your opinion. In v7 implementation: if probe on func+4, that's bl ftrace-entry, similar as mcount call on other architectures, we allow this probe as normal. if probe on func+0, the first param ip in kprobe_ftrace_handler() points to func+4(this is adjusted by ftrace), regs->ip points to func+8, so in kprobe_ftrace_handler() we modify regs->ip to func+0 to call kprobe pre handler, then modify regs->ip to func+8 to call kprobe post handler. As can be seen, the first two instructions are considered as a virtual mcount call. From this point of view, lr saver and the bl is coupled. If we split patch3 into two: one to support kprobes func+4 the second to support kprobe on func+0 it would be much clearer. Then the key here is whether we could allow both kprobes on func+0 and func= +4 Thanks