linux-arm-kernel.lists.infradead.org archive mirror
 help / color / mirror / Atom feed
From: Mark Rutland <mark.rutland@arm.com>
To: Wang ShaoBo <bobo.shaobowang@huawei.com>
Cc: cj.chengjian@huawei.com, huawei.libin@huawei.com,
	xiexiuqi@huawei.com, liwei391@huawei.com,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com,
	will@kernel.org, rostedt@goodmis.org, zengshun.wu@outlook.com
Subject: Re: [RFC PATCH -next v2 0/4] arm64/ftrace: support dynamic trampoline
Date: Thu, 21 Apr 2022 13:53:44 +0100	[thread overview]
Message-ID: <YmFT2DtlcQd7k4Tt@lakrids> (raw)
In-Reply-To: <20220316100132.244849-1-bobo.shaobowang@huawei.com>

On Wed, Mar 16, 2022 at 06:01:28PM +0800, Wang ShaoBo wrote:
> This implements dynamic trampoline in ARM64, as reference said, we
> complete whole design of supporting long jump in dynamic trampoline:
> 
>    .text section:
>      funcA:         |    funcA():        funcB():|
>       `->  +-----+  |    |   ...         mov x9  |
>            | ... |  |    |   adrp   <-   bl  <>  |
>            | nop |  |    |   mov
>            | nop |  |    |   br   x16 ---+
>      funcB | nop |  |                    | ftrace_(regs_)caller_tramp:
>       `->  +-----+  |                    `--> +---------------------+
>            | nop |  |                         | ...                 |
>            | nop |  |       ftrace callsite   +---------------------+
>            | ... |  |                `----->  | PLT entry:          |
>            | nop |  |                         |       adrp          |
>            | nop |  |                         |       add           |
>     funcC: | nop |  | ftrace graph callsite   |       br   x16      |
>       `->  +-----+  |                `----->  +---------------------+
>            | nop |  |                         | ...                 |
>            | nop |  |                         +---------------------+
> 
> But there is still a tricky problem that is how to adjust tracing ip,
> waiting to be solved:
> 
> For ARM64, somecases there may be extra instructions inserted into the
> head of tracable functions(but not all) by compiler, for instance BTI[1].
> 
> This dump vmlinux with CONFIG_BTI=y:
> 
> (1) function gic_handle_irq has bti in its head, so we adjust rec->ip+=5 to last nop
>     ffffffc0080100e0:       d53cd042        mrs     x2, tpidr_el2
>             ...
>     ffffffc0080100f0:       d503201f        nop     //__mcount_loc tells the rec->ip
>     ffffffc0080100f4:       d503201f        nop
>     ffffffc0080100f8:       d503201f        nop
> 
>     ffffffc0080100fc <gic_handle_irq>:
>     ffffffc0080100fc:       d503245f        bti     c
>     ffffffc008010100:       d503201f        nop
>     ffffffc008010104:       d503201f        nop     //we adjust origin rec->ip+5 to here
>     ffffffc008010108:       d503233f        paciasp
> (2) name_to_dev_t.part.0 do not has bti in its head, so we should adjust rec->ip+=4 to last nop
>     ffff8000080137d4:       d503201f        nop
>     ffff8000080137d8:       d503201f        nop
>     ffff8000080137dc:       d503201f        nop
>     
>     ffff8000080137e0 <name_to_dev_t.part.0>:
>     ffff8000080137e0:       d503201f        nop
>     ffff8000080137e4:       d503201f        nop
>     ffff8000080137e8:       d503233f        paciasp
> 
> So at this time we have no idea to identify rec->ip for each tracable function.

When I had looked into this in the past, I had assumed we could figure
this out at ftrace_init_nop() time, and adjust rec->ip there.

However, placing code *before* the function entry point will also break
stacktracing and will require adjustment, and I'd been intending to
clean up the stacktrace code first, so I haven't looked at that in a
while.

I'll take a look at the rest of the series shortly.

Thanks,
Mark.

> 
> we are looking forward to follow-up discussions.
> 
> References:
> [1] https://developer.arm.com/documentation/100076/0100/a64-instruction-set-reference/a64-general-instructions/bti
> [2] https://lore.kernel.org/linux-arm-kernel/20200109142736.1122-1-cj.chengjian@huawei.com/
> 
> Cheng Jian (4):
>   arm64: introduce aarch64_insn_gen_load_literal
>   arm64/ftrace: introduce ftrace dynamic trampoline entrances
>   arm64/ftrace: support dynamically allocated trampolines
>   arm64/ftrace: implement long jump for dynamic trampolines
> 
>  arch/arm64/Makefile              |   2 +-
>  arch/arm64/include/asm/ftrace.h  |  10 +-
>  arch/arm64/include/asm/insn.h    |   6 +
>  arch/arm64/include/asm/module.h  |   9 +
>  arch/arm64/kernel/entry-ftrace.S |  88 ++++++--
>  arch/arm64/kernel/ftrace.c       | 366 ++++++++++++++++++++++++++++---
>  arch/arm64/kernel/module-plts.c  |  50 +++++
>  arch/arm64/lib/insn.c            |  49 +++++
>  8 files changed, 532 insertions(+), 48 deletions(-)
> 
> -- 
> 2.25.1
> 

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

      parent reply	other threads:[~2022-04-21 12:55 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-16 10:01 [RFC PATCH -next v2 0/4] arm64/ftrace: support dynamic trampoline Wang ShaoBo
2022-03-16 10:01 ` [RFC PATCH -next v2 1/4] arm64: introduce aarch64_insn_gen_load_literal Wang ShaoBo
2022-03-16 10:01 ` [RFC PATCH -next v2 2/4] arm64/ftrace: introduce ftrace dynamic trampoline entrances Wang ShaoBo
2022-03-16 10:01 ` [RFC PATCH -next v2 3/4] arm64/ftrace: support dynamically allocated trampolines Wang ShaoBo
2022-04-21 13:10   ` Mark Rutland
2022-04-21 14:06     ` Steven Rostedt
2022-04-21 14:08       ` Steven Rostedt
2022-04-21 15:14       ` Mark Rutland
2022-04-21 15:42         ` Steven Rostedt
2022-04-21 16:27           ` Mark Rutland
2022-04-21 17:06             ` Steven Rostedt
2022-04-22 10:12               ` Mark Rutland
2022-04-22 15:45                 ` Steven Rostedt
2022-04-22 17:27                   ` Mark Rutland
2022-04-26  8:47                     ` Masami Hiramatsu
2022-05-04 10:24                       ` Mark Rutland
2022-05-05  3:15                         ` Masami Hiramatsu
2022-05-09 18:22                           ` Steven Rostedt
2022-05-10  9:10                             ` Masami Hiramatsu
2022-05-10 14:44                               ` Steven Rostedt
2022-05-11 14:34                                 ` Masami Hiramatsu
2022-05-11 15:12                                   ` Steven Rostedt
2022-05-12 12:02                                     ` Masami Hiramatsu
2022-05-12 13:50                                       ` Steven Rostedt
2022-05-25 12:17                                       ` Mark Rutland
2022-05-25 13:43                                         ` Steven Rostedt
2022-05-25 17:12                                           ` Mark Rutland
2022-05-30  1:03                                         ` Masami Hiramatsu
2022-05-30 12:38                                           ` Jiri Olsa
2022-05-31  1:00                                             ` Masami Hiramatsu
2022-05-04 12:43               ` Mark Rutland
2022-05-05  2:57             ` Wangshaobo (bobo)
2022-05-25 12:27               ` Mark Rutland
2022-04-27  8:54       ` Wangshaobo (bobo)
2022-03-16 10:01 ` [RFC PATCH -next v2 4/4] arm64/ftrace: implement long jump for dynamic trampolines Wang ShaoBo
2022-04-21 13:47   ` Mark Rutland
2022-03-16 14:29 ` [RFC PATCH -next v2 0/4] arm64/ftrace: support dynamic trampoline Steven Rostedt
2022-04-20 18:11 ` Steven Rostedt
2022-04-21  1:13   ` Wangshaobo (bobo)
2022-04-21 12:37     ` Steven Rostedt
2022-05-25 12:45       ` Mark Rutland
2022-05-25 13:58         ` Steven Rostedt
2022-05-25 17:26           ` Mark Rutland
2022-04-21 12:53 ` Mark Rutland [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=YmFT2DtlcQd7k4Tt@lakrids \
    --to=mark.rutland@arm.com \
    --cc=bobo.shaobowang@huawei.com \
    --cc=catalin.marinas@arm.com \
    --cc=cj.chengjian@huawei.com \
    --cc=huawei.libin@huawei.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=liwei391@huawei.com \
    --cc=rostedt@goodmis.org \
    --cc=will@kernel.org \
    --cc=xiexiuqi@huawei.com \
    --cc=zengshun.wu@outlook.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).