From: Peter Zijlstra <peterz@infradead.org>
To: Julien Thierry <jthierry@redhat.com>
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: Wed, 1 Apr 2020 19:09:10 +0200 [thread overview]
Message-ID: <20200401170910.GX20730@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <d2cad75e-1708-f0bf-7f88-194bcb29e61d@redhat.com>
On Wed, Apr 01, 2020 at 04:43:35PM +0100, Julien Thierry wrote:
> > +static bool has_modified_stack_frame(struct instruction *insn, struct insn_state *state)
> > {
> > + u8 ret_offset = insn->ret_offset;
> > int i;
> >
> > - if (state->cfa.base != initial_func_cfi.cfa.base ||
> > - state->cfa.offset != initial_func_cfi.cfa.offset ||
> > - state->stack_size != initial_func_cfi.cfa.offset ||
> > - state->drap)
> > + if (state->cfa.base != initial_func_cfi.cfa.base || state->drap)
> > + return true;
> > +
> > + if (state->cfa.offset != initial_func_cfi.cfa.offset &&
> > + !(ret_offset && state->cfa.offset == initial_func_cfi.cfa.offset + ret_offset))
>
> Isn't that the same thing as "state->cfa.offset !=
> initial_func_cfi.cfa.offset + ret_offset" ?
I'm confused on what cfa.offset is, sometimes it increase with
stack_size, sometimes it doesn't.
ISTR that for the ftrace case it was indeed cfa.offset + 8, but for the
IRET case below (where it is now not used anymore) it was cfa.offset
(not cfa.offset + 40, which I was expecting).
> > + return true;
> > +
> > + if (state->stack_size != initial_func_cfi.cfa.offset + ret_offset)
> > return true;
> >
> > - for (i = 0; i < CFI_NUM_REGS; i++)
> > + for (i = 0; i < CFI_NUM_REGS; i++) {
> > if (state->regs[i].base != initial_func_cfi.regs[i].base ||
> > state->regs[i].offset != initial_func_cfi.regs[i].offset)
> > return true;
> > + }
> >
> > return false;
> > }
> > @@ -2185,6 +2148,13 @@ static int validate_branch(struct objtoo
> >
> > break;
> >
> > + case INSN_EXCEPTION_RETURN:
> > + if (func) {
> > + state.stack_size -= arch_exception_frame_size;
> > + break;
>
> Why break instead of returning? Shouldn't an exception return mark the end
> of a branch (whether inside or outside a function) ?
>
> Here it seems it will continue to the next instruction which might have been
> unreachable.
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.
> > + }
> > +
> > + /* fallthrough */
>
> What is the purpose of the fallthrough here? If the exception return was in
> a function, it carried on to the next instruction, so it won't use the
> WARN_FUNC(). So, if I'm looking at the right version of the code only the
> "return 0;" will be used. And, unless my previous comment is wrong, I'd
> argue that we should return both for func and !func.
That came from the fact that we split it out of INSN_CONTEXT_SWITCH.
You're right that it has now reduced to just return 0.
> > case INSN_CONTEXT_SWITCH:
> > if (func && (!next_insn || !next_insn->hint)) {
> > WARN_FUNC("unsupported instruction in callable function",
next prev parent reply other threads:[~2020-04-01 17:09 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 [this message]
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
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=20200401170910.GX20730@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=jpoimboe@redhat.com \
--cc=jthierry@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mbenes@suse.cz \
--cc=mhiramat@kernel.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).