From: Julien Thierry <jthierry@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
tglx@linutronix.de, linux-kernel@vger.kernel.org, x86@kernel.org,
mhiramat@kernel.org, mbenes@suse.cz,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH v2] objtool,ftrace: Implement UNWIND_HINT_RET_OFFSET
Date: Thu, 2 Apr 2020 09:16:50 +0100 [thread overview]
Message-ID: <30b3df44-6254-b5a7-2f5d-0bc071adb00e@redhat.com> (raw)
In-Reply-To: <20200402075036.GA20730@hirez.programming.kicks-ass.net>
On 4/2/20 8:50 AM, Peter Zijlstra wrote:
> On Thu, Apr 02, 2020 at 07:41:46AM +0100, Julien Thierry wrote:
>> On 4/1/20 6:09 PM, Peter Zijlstra wrote:
>
>>> The code in question (x86's sync_core()), is an exception return to
>>> self. It pushes an exception frame that points to right after the
>>> exception return instruction.
>>>
>>> This is the only usage of IRET in STT_FUNC symbols.
>>>
>>> So rather than teaching objtool how to interpret the whole
>>> push;push;push;push;push;iret sequence, teach it how big the frame is
>>> (arch_exception_frame_size) and let it continue.
>>>
>>> All the other (real) IRETs are in STT_NOTYPE in the entry assembly.
>>>
>>
>> Right, I see.. However I'm not completely convinced by this. I must admit I
>> haven't followed the whole conversation, but what was the issue with the
>> HINT_IRET_SELF? It seemed more elegant, but I might be missing some context.
>
> https://lkml.kernel.org/r/20200331211755.pb7f3wa6oxzjnswc@treble
>
> Josh didn't think it was worth it, I think.
>
>> Otherwise, it might be worth having a comment in the code to point that this
>> only handles the sync_core() case.
>
> I can certainly do that. Does ARM have any ERETs sprinkled around in
> places it should not have? That is, is this going to be a problem for
> you?
>
I had a quick look and I don't think there are ERETS in function
symbols. And, worst case scenario, I could also just keep the arm64
decoder making ERETS as INSN_CONTEXT_SWITCH as I didn't need more
semantics so far (and arm64 ERET don't affect the stack anyway).
After you pointed out this only affect this very specific pattern, I
admit that my concerns are more about "not having weird stuff in the
generic part".
If it's too much of a hassle I can understand if you prefer to just put
a comment. But if most of this can be kept to the arch specific decoder
I think it'd be nicer :) .
>> Also, instead of adding a special "arch_exception_frame_size", I could
>> suggest:
>> - Picking this patch [1] from a completely arbitrary source
>> - Getting rid of INSN_STACK type, any instruction could then include stack
>> ops on top of their existing semantics, they can just have an empty list if
>> they don't touch SP/BP
>> - x86 decoder adds a stack_op to the iret to modify the stack pointer by the
>> right amount
>
> That's not the worst idea, lemme try that.
>
Thanks, keep me in Cc if you post a new version using that!
Cheers,
--
Julien Thierry
next prev parent reply other threads:[~2020-04-02 8:17 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-25 17:45 [PATCH v4 00/13] objtool: vmlinux.o and moinstr validation Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 01/13] objtool: Remove CFI save/restore special case Peter Zijlstra
2020-03-26 11:30 ` Peter Zijlstra
2020-03-26 12:58 ` Peter Zijlstra
2020-03-26 13:44 ` Josh Poimboeuf
2020-03-26 15:38 ` Peter Zijlstra
2020-03-27 4:19 ` Josh Poimboeuf
2020-03-26 14:44 ` Miroslav Benes
2020-03-26 15:04 ` Miroslav Benes
2020-03-26 13:00 ` Peter Zijlstra
2020-03-26 13:56 ` Josh Poimboeuf
2020-03-26 15:49 ` Peter Zijlstra
2020-03-26 19:57 ` Peter Zijlstra
2020-03-27 1:00 ` Josh Poimboeuf
2020-03-30 17:02 ` Peter Zijlstra
2020-03-30 19:02 ` Josh Poimboeuf
2020-03-30 20:02 ` Peter Zijlstra
2020-03-30 20:29 ` Peter Zijlstra
2020-03-31 11:16 ` [RFC][PATCH] objtool,ftrace: Implement UNWIND_HINT_RET_OFFSET Peter Zijlstra
2020-03-31 15:31 ` Steven Rostedt
2020-03-31 16:06 ` [RFC][PATCH] x86,ftrace: Shrink ftrace_regs_caller() by one byte Peter Zijlstra
2020-03-31 19:58 ` [RFC][PATCH] objtool,ftrace: Implement UNWIND_HINT_RET_OFFSET Peter Zijlstra
2020-03-31 20:26 ` Josh Poimboeuf
2020-03-31 20:23 ` Josh Poimboeuf
2020-03-31 20:40 ` Peter Zijlstra
2020-03-31 21:07 ` Peter Zijlstra
2020-03-31 21:17 ` Josh Poimboeuf
2020-03-31 21:20 ` Josh Poimboeuf
2020-03-31 22:27 ` [PATCH v2] " Peter Zijlstra
2020-04-01 14:14 ` Josh Poimboeuf
2020-04-01 14:22 ` Peter Zijlstra
2020-04-01 14:39 ` Josh Poimboeuf
2020-04-01 15:38 ` Peter Zijlstra
2020-04-01 15:39 ` Steven Rostedt
2020-04-01 15:43 ` Julien Thierry
2020-04-01 17:09 ` Peter Zijlstra
2020-04-01 17:33 ` Steven Rostedt
2020-04-01 17:45 ` Peter Zijlstra
2020-04-01 18:20 ` Steven Rostedt
2020-04-01 20:20 ` Peter Zijlstra
2020-04-01 17:37 ` Josh Poimboeuf
2020-04-02 6:41 ` Julien Thierry
2020-04-02 6:56 ` Julien Thierry
2020-04-02 7:50 ` Peter Zijlstra
2020-04-02 8:16 ` Julien Thierry [this message]
2020-04-02 8:17 ` Peter Zijlstra
2020-04-02 8:29 ` Julien Thierry
2020-04-02 8:58 ` Miroslav Benes
2020-03-25 17:45 ` [PATCH v4 02/13] objtool: Factor out CFI hints Peter Zijlstra
2020-03-25 18:26 ` Miroslav Benes
2020-03-25 19:41 ` Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 03/13] objtool: Rename struct cfi_state Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 04/13] objtool: Fix !CFI insn_state propagation Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 05/13] objtool: Implement noinstr validation Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 06/13] objtool: Optimize !vmlinux.o again Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 07/13] objtool: Use sec_offset_hash() for insn_hash Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 08/13] objtool: Detect loading function pointers across noinstr Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 09/13] kbuild/objtool: Add objtool-vmlinux.o pass Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 10/13] objtool: Avoid iterating !text section symbols Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 11/13] objtool: Rearrange validate_section() Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 12/13] objtool: Add STT_NOTYPE noinstr validation Peter Zijlstra
2020-03-25 17:45 ` [PATCH v4 13/13] objtool: Also consider .entry.text as noinstr Peter Zijlstra
2020-03-25 19:03 ` [PATCH v4 00/13] objtool: vmlinux.o and moinstr validation Miroslav Benes
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=30b3df44-6254-b5a7-2f5d-0bc071adb00e@redhat.com \
--to=jthierry@redhat.com \
--cc=jpoimboe@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mbenes@suse.cz \
--cc=mhiramat@kernel.org \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/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).