From: jpoimboe@redhat.com (Josh Poimboeuf)
Subject: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions
Date: Tue, 7 May 2019 12:21:59 -0500 [thread overview]
Message-ID: <20190507172159.5t3bm3mjkwagvite@treble> (raw)
Message-ID: <20190507172159.s_eHlEQ6ZEKU16Zs2C9-KXztkrkeV-ZicgVXzdir4b0@z> (raw)
In-Reply-To: <CAHk-=wiuue37opWK5QaQ9f6twqDZuSratdP-1bK6kD9-Az5WnA@mail.gmail.com>
On Tue, May 07, 2019@10:08:50AM -0700, Linus Torvalds wrote:
> On Tue, May 7, 2019@9:34 AM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > Would you consider my approach later on, under the guise of unification?
>
> WHY?
>
> The *only* advantage of your patch is that trivial "look up kernel stack" macro.
>
> Seriously. There's absolutely nothing else.
>
> Is that macro ugly? Yes. But it's directly explainable by just
> pointing to the architecture documentation.
>
> It's a one-liner hack.
>
> And for that, you want to complicate the x86-32 entry and exit code?
>
> Do we have different emulation for "push" on 32-bit and 64-bit? Yes.
> But again, that's just how the hardware works. This is not some
> "generic hw-independent code". This is literally emulating
> instructions that care about instruction encoding and bit size
> details, where there are certainly _similarities_ (and in the case of
> 'call', they look bit-identical), but it's also not like "same code"
> is a big argument. That's why we have a helper function, to hide the
> details.
>
> I point to my diffstat once again. It's smaller, and I argue that it
> is actually conceptually *simpler* to simply say "this is how the
> architecture works".
>
> And yes, I realize that I may be biased by the fact that I simply know
> i386 so well, so to me it simply makes more sense to just work with
> what the hardware gives us. The i386 exception model with the kernel
> stack nesting is a *hell* of a lot simpler than the x86-64 one. The
> fact is, x86-64 messed things up, and swapgs and friends are an
> abomination against God.
>
> So the whole "let's clean up x86-32 to look like x86-64, which got
> things right" is to me a completely bogus argument. x86-64 got the
> "yes, push ss/sp unconditionally" part right, but got a lot of other
> things horribly wrong. So this is all just one small detail that
> differs, across two architectures that are similar but have very
> different warts.
>
> But that diffstat is still hard, cold, unbiased data.
regs->sp is *undefined* on x86-32. We're damning our future selves to
have to always remember to use that darn kernel_stack_pointer() helper
for eternity just because of x86-32.
There have already been several bugs related to that. Because regs->sp
is there, so why wouldn't you use it?
If we truly want the code to reflect the HW, then we should have a
pt_regs_kernel and a pt_regs_user on 32-bit. I'm pretty sure we don't
want to go there...
IMO, we either need to make the pt_regs struct(s) match the HW behavior,
or make entry code match pt_regs. But this in-between thing just
creates a bunch of headaches.
--
Josh
next prev parent reply other threads:[~2019-05-07 17:21 UTC|newest]
Thread overview: 204+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190501202830.347656894@goodmis.org>
2019-05-01 20:28 ` [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions rostedt
2019-05-01 20:28 ` Steven Rostedt
2019-05-02 3:24 ` rostedt
2019-05-02 3:24 ` Steven Rostedt
2019-05-02 16:21 ` peterz
2019-05-02 16:21 ` Peter Zijlstra
2019-05-02 16:29 ` peterz
2019-05-02 16:29 ` Peter Zijlstra
2019-05-02 18:02 ` torvalds
2019-05-02 18:02 ` Linus Torvalds
2019-05-02 18:18 ` peterz
2019-05-02 18:18 ` Peter Zijlstra
2019-05-02 18:30 ` peterz
2019-05-02 18:30 ` Peter Zijlstra
2019-05-02 18:43 ` torvalds
2019-05-02 18:43 ` Linus Torvalds
2019-05-02 19:28 ` jikos
2019-05-02 19:28 ` Jiri Kosina
2019-05-02 20:25 ` luto
2019-05-02 20:25 ` Andy Lutomirski
2019-05-02 20:21 ` peterz
2019-05-02 20:21 ` Peter Zijlstra
2019-05-02 20:49 ` torvalds
2019-05-02 20:49 ` Linus Torvalds
2019-05-02 21:32 ` peterz
2019-05-02 21:32 ` Peter Zijlstra
2019-05-03 19:24 ` rostedt
2019-05-03 19:24 ` Steven Rostedt
2019-05-03 21:46 ` torvalds
2019-05-03 21:46 ` Linus Torvalds
2019-05-03 22:49 ` rostedt
2019-05-03 22:49 ` Steven Rostedt
2019-05-03 23:07 ` torvalds
2019-05-03 23:07 ` Linus Torvalds
2019-05-04 4:17 ` rostedt
2019-05-04 4:17 ` Steven Rostedt
[not found] ` <CAHk-=wiuSFbv_rELND-BLWcP0GSZ0yF=xOAEcf61GE3bU9d=yg@mail.gmail.com>
2019-05-04 18:59 ` torvalds
2019-05-04 18:59 ` Linus Torvalds
2019-05-04 20:12 ` luto
2019-05-04 20:12 ` Andy Lutomirski
2019-05-04 20:28 ` torvalds
2019-05-04 20:28 ` Linus Torvalds
2019-05-04 20:36 ` torvalds
2019-05-04 20:36 ` Linus Torvalds
2019-05-03 22:55 ` luto
2019-05-03 22:55 ` Andy Lutomirski
2019-05-03 23:16 ` torvalds
2019-05-03 23:16 ` Linus Torvalds
2019-05-03 23:32 ` luto
2019-05-03 23:32 ` Andy Lutomirski
2019-05-02 22:52 ` rostedt
2019-05-02 22:52 ` Steven Rostedt
2019-05-02 23:31 ` rostedt
2019-05-02 23:31 ` Steven Rostedt
2019-05-02 23:50 ` rostedt
2019-05-02 23:50 ` Steven Rostedt
2019-05-03 1:51 ` [RFC][PATCH 1/2 v2] " rostedt
2019-05-03 1:51 ` Steven Rostedt
2019-05-03 9:29 ` [RFC][PATCH 1/2] " peterz
2019-05-03 9:29 ` Peter Zijlstra
2019-05-03 13:22 ` rostedt
2019-05-03 13:22 ` Steven Rostedt
2019-05-03 16:20 ` luto
2019-05-03 16:20 ` Andy Lutomirski
2019-05-03 16:31 ` rostedt
2019-05-03 16:31 ` Steven Rostedt
2019-05-03 16:35 ` peterz
2019-05-03 16:35 ` Peter Zijlstra
2019-05-03 16:44 ` luto
2019-05-03 16:44 ` Andy Lutomirski
2019-05-03 16:49 ` rostedt
2019-05-03 16:49 ` Steven Rostedt
2019-05-03 16:32 ` peterz
2019-05-03 16:32 ` Peter Zijlstra
2019-05-03 18:57 ` torvalds
2019-05-03 18:57 ` Linus Torvalds
2019-05-06 8:19 ` peterz
2019-05-06 8:19 ` Peter Zijlstra
2019-05-06 13:56 ` rostedt
2019-05-06 13:56 ` Steven Rostedt
2019-05-06 16:17 ` torvalds
2019-05-06 16:17 ` Linus Torvalds
2019-05-06 16:19 ` torvalds
2019-05-06 16:19 ` Linus Torvalds
2019-05-06 17:06 ` rostedt
2019-05-06 17:06 ` Steven Rostedt
2019-05-06 18:06 ` torvalds
2019-05-06 18:06 ` Linus Torvalds
2019-05-06 18:57 ` rostedt
2019-05-06 18:57 ` Steven Rostedt
2019-05-06 19:46 ` torvalds
2019-05-06 19:46 ` Linus Torvalds
2019-05-06 20:29 ` rostedt
2019-05-06 20:29 ` Steven Rostedt
2019-05-06 20:42 ` torvalds
2019-05-06 20:42 ` Linus Torvalds
2019-05-06 20:44 ` torvalds
2019-05-06 20:44 ` Linus Torvalds
2019-05-06 21:45 ` rostedt
2019-05-06 21:45 ` Steven Rostedt
2019-05-06 22:06 ` torvalds
2019-05-06 22:06 ` Linus Torvalds
2019-05-06 22:31 ` torvalds
2019-05-06 22:31 ` Linus Torvalds
2019-05-07 0:10 ` rostedt
2019-05-07 0:10 ` Steven Rostedt
2019-05-07 1:06 ` torvalds
2019-05-07 1:06 ` Linus Torvalds
2019-05-07 1:04 ` rostedt
2019-05-07 1:04 ` Steven Rostedt
2019-05-07 1:34 ` rostedt
2019-05-07 1:34 ` Steven Rostedt
2019-05-07 1:34 ` torvalds
2019-05-07 1:34 ` Linus Torvalds
2019-05-07 1:53 ` rostedt
2019-05-07 1:53 ` Steven Rostedt
2019-05-07 2:22 ` torvalds
2019-05-07 2:22 ` Linus Torvalds
2019-05-07 2:58 ` rostedt
2019-05-07 2:58 ` Steven Rostedt
2019-05-07 3:05 ` torvalds
2019-05-07 3:05 ` Linus Torvalds
2019-05-07 3:21 ` rostedt
2019-05-07 3:21 ` Steven Rostedt
2019-05-07 3:28 ` torvalds
2019-05-07 3:28 ` Linus Torvalds
2019-05-07 14:54 ` torvalds
2019-05-07 14:54 ` Linus Torvalds
2019-05-07 15:12 ` rostedt
2019-05-07 15:12 ` Steven Rostedt
2019-05-07 15:25 ` rostedt
2019-05-07 15:25 ` Steven Rostedt
2019-05-07 16:25 ` rostedt
2019-05-07 16:25 ` Steven Rostedt
2019-05-07 15:31 ` torvalds
2019-05-07 15:31 ` Linus Torvalds
2019-05-07 15:45 ` rostedt
2019-05-07 15:45 ` Steven Rostedt
2019-05-07 16:34 ` peterz
2019-05-07 16:34 ` Peter Zijlstra
2019-05-07 17:08 ` torvalds
2019-05-07 17:08 ` Linus Torvalds
2019-05-07 17:21 ` jpoimboe [this message]
2019-05-07 17:21 ` Josh Poimboeuf
2019-05-07 21:24 ` rostedt
2019-05-07 21:24 ` Steven Rostedt
2019-05-08 4:50 ` torvalds
2019-05-08 4:50 ` Linus Torvalds
2019-05-08 16:37 ` rostedt
2019-05-08 16:37 ` Steven Rostedt
2019-05-07 17:38 ` peterz
2019-05-07 17:38 ` Peter Zijlstra
2019-05-07 9:51 ` peterz
2019-05-07 9:51 ` Peter Zijlstra
2019-05-07 14:48 ` luto
2019-05-07 14:48 ` Andy Lutomirski
2019-05-07 14:57 ` torvalds
2019-05-07 14:57 ` Linus Torvalds
2019-05-07 14:13 ` mhiramat
2019-05-07 14:13 ` Masami Hiramatsu
2019-05-07 17:15 ` mhiramat
2019-05-07 17:15 ` Masami Hiramatsu
2019-05-06 14:22 ` peterz
2019-05-06 14:22 ` Peter Zijlstra
2019-05-07 8:57 ` peterz
2019-05-07 8:57 ` Peter Zijlstra
2019-05-07 9:18 ` David.Laight
2019-05-07 9:18 ` David Laight
2019-05-07 11:30 ` peterz
2019-05-07 11:30 ` Peter Zijlstra
2019-05-07 12:57 ` David.Laight
2019-05-07 12:57 ` David Laight
2019-05-07 13:14 ` rostedt
2019-05-07 13:14 ` Steven Rostedt
2019-05-07 14:50 ` David.Laight
2019-05-07 14:50 ` David Laight
2019-05-07 14:57 ` rostedt
2019-05-07 14:57 ` Steven Rostedt
2019-05-07 15:46 ` David.Laight
2019-05-07 15:46 ` David Laight
2019-05-07 13:32 ` peterz
2019-05-07 13:32 ` Peter Zijlstra
2019-05-07 9:27 ` peterz
2019-05-07 9:27 ` Peter Zijlstra
2019-05-07 12:27 ` rostedt
2019-05-07 12:27 ` Steven Rostedt
2019-05-07 12:41 ` peterz
2019-05-07 12:41 ` Peter Zijlstra
2019-05-07 12:54 ` rostedt
2019-05-07 12:54 ` Steven Rostedt
2019-05-07 17:22 ` masami.hiramatsu
2019-05-07 17:22 ` Masami Hiramatsu
2019-05-07 14:28 ` peterz
2019-05-07 14:28 ` Peter Zijlstra
2019-05-02 20:48 ` rostedt
2019-05-02 20:48 ` Steven Rostedt
2019-05-06 15:14 ` jpoimboe
2019-05-06 15:14 ` Josh Poimboeuf
2019-05-01 20:28 ` [RFC][PATCH 2/2] ftrace/x86: Emulate call function while updating in breakpoint handler rostedt
2019-05-01 20:28 ` Steven Rostedt
2019-05-03 10:22 ` [RFC][PATCH 1.5/2] x86: Add int3_emulate_call() selftest peterz
2019-05-03 10:22 ` Peter Zijlstra
2019-05-03 18:46 ` rostedt
2019-05-03 18:46 ` Steven Rostedt
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