From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org, x86@kernel.org,
mhiramat@kernel.org, mbenes@suse.cz,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [RFC][PATCH] objtool,ftrace: Implement UNWIND_HINT_RET_OFFSET
Date: Tue, 31 Mar 2020 15:23:15 -0500 [thread overview]
Message-ID: <20200331202315.zialorhlxmml6ec7@treble> (raw)
In-Reply-To: <20200331111652.GH20760@hirez.programming.kicks-ass.net>
On Tue, Mar 31, 2020 at 01:16:52PM +0200, Peter Zijlstra wrote:
> Subject: objtool,ftrace: Implement UNWIND_HINT_RET_OFFSET
>
> This replaces the SAVE/RESTORE hints with a RET_OFFSET hint that applies
> to the following instructions:
>
> - any instruction that terminates a function, like: RETURN and sibling
> calls. It allows the stack-frame to be off by @sp_offset, ie. it
> allows stuffing the return stack.
>
> - EXCEPTION_RETURN (a new INSN_type that splits IRET out of
> CONTEXT_SWITCH) and here it denotes a @sp_offset sized POP and makes
> the instruction continue.
Looking closer, I see how my UNWIND_HINT_ADJUST idea doesn't work for
the ftrace_regs_caller() case. The ORC data is actually correct there.
So basically we need a way to tell objtool to be quiet.
I now understand what you're trying to do with the RET_TAIL thing, and I
guess it's ok for the ftrace case. But I'd rather an UNWIND_HINT_IGNORE
before the tail cail, which would tell objtool to just silence the tail
call warning. It's simpler for the user to understand, it's simpler
logic in objtool, and I think an "ignore warnings for the next insn"
hint would be more generally applicable anyway.
But also... the RET_OFFSET usage for sync_core() *really* bugs me.
I know you said it's like an indirect tail call with a bigger frame, but
that's kind of stretching it because the function frame is still there.
And objtool doesn't treat it like a tail call at all. In fact, it
handles it *completely* differently from the normal ret-tail-call case.
Instead of silencing a tail call warning, it adjusts the stack offset
and continues the code path.
This basically adds *two* new hint types, while trying to call them the
same thing. There's no overlapping functionality between them in
objtool, other than the use of the same insn->ret_offset variable. But
it's two distinct functionalities, depending on the context (return/tail
vs IRETQ).
I'll try to work up some patches with a different approach in a bit.
--
Josh
next prev parent reply other threads:[~2020-03-31 20:23 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 [this message]
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
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
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