From: Josh Poimboeuf <jpoimboe@redhat•com>
To: Nicholas Piggin <npiggin@gmail•com>
Cc: Torsten Duwe <duwe@lst•de>,
linux-kernel@vger•kernel.org, Jiri Kosina <jkosina@suse•cz>,
live-patching@vger•kernel.org, linuxppc-dev@lists•ozlabs.org
Subject: Re: [PATCH] On ppc64le we HAVE_RELIABLE_STACKTRACE
Date: Sun, 17 Dec 2017 20:58:54 -0600 [thread overview]
Message-ID: <20171218025854.angid7h33gnmxsrg@treble> (raw)
In-Reply-To: <20171215194009.349b04da@roar.ozlabs.ibm.com>
On Fri, Dec 15, 2017 at 07:40:09PM +1000, Nicholas Piggin wrote:
> On Tue, 12 Dec 2017 08:05:01 -0600
> Josh Poimboeuf <jpoimboe@redhat•com> wrote:
>
> > On Tue, Dec 12, 2017 at 12:39:12PM +0100, Torsten Duwe wrote:
> > > Hi all,
> > >
> > > The "Power Architecture 64-Bit ELF V2 ABI" says in section 2.3.2.3:
> > >
> > > [...] There are several rules that must be adhered to in order to ensure
> > > reliable and consistent call chain backtracing:
> > >
> > > * Before a function calls any other function, it shall establish its
> > > own stack frame, whose size shall be a multiple of 16 bytes.
> >
> > What about leaf functions? If a leaf function doesn't establish a stack
> > frame, and it has inline asm which contains a blr to another function,
> > this ABI is broken.
Oops, I meant to say "bl" instead of "blr".
> > Also, even for non-leaf functions, is it possible for GCC to insert the
> > inline asm before it sets up the stack frame? (This is an occasional
> > problem on x86.)
>
> Inline asm must not have control transfer out of the statement unless
> it is asm goto.
Can inline asm have calls to other functions?
> > Also, what about hand-coded asm?
>
> Should follow the same rules if it uses the stack.
How is that enforced?
> > > To me this sounds like the equivalent of HAVE_RELIABLE_STACKTRACE.
> > > This patch may be unneccessarily limited to ppc64le, but OTOH the only
> > > user of this flag so far is livepatching, which is only implemented on
> > > PPCs with 64-LE, a.k.a. ELF ABI v2.
> >
> > In addition to fixing the above issues, the unwinder also needs to
> > detect interrupts (i.e., preemption) and page faults on the stack of a
> > blocked task. If a function were preempted before it created a stack
> > frame, or if a leaf function blocked on a page fault, the stack trace
> > will skip the function's caller, so such a trace will need to be
> > reported to livepatch as unreliable.
>
> I don't think there is much problem there for powerpc. Stack frame
> creation and function call with return pointer are each atomic.
What if the function is interrupted before it creates the stack frame?
--
Josh
next prev parent reply other threads:[~2017-12-18 2:58 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-04 15:25 [PATCH v2] kernel/module_64.c: Add REL24 relocation support of livepatch symbols Kamalesh Babulal
2017-10-05 6:56 ` Naveen N . Rao
2017-10-05 12:43 ` Torsten Duwe
2017-10-06 5:43 ` Kamalesh Babulal
2017-10-11 9:44 ` Kamalesh Babulal
2017-10-06 5:57 ` Kamalesh Babulal
2017-10-17 14:47 ` Torsten Duwe
2017-10-18 6:17 ` Kamalesh Babulal
2017-10-20 12:07 ` Torsten Duwe
2017-10-21 0:59 ` Balbir Singh
2017-10-23 8:19 ` Kamalesh Babulal
2017-12-12 11:39 ` [PATCH] On ppc64le we HAVE_RELIABLE_STACKTRACE Torsten Duwe
2017-12-12 12:12 ` Miroslav Benes
2017-12-12 13:02 ` Torsten Duwe
2018-02-27 16:09 ` [PATCH 2/2] ppc64le save_stack_trace_tsk_reliable (Was: HAVE_RELIABLE_STACKTRACE) Torsten Duwe
2018-03-08 21:43 ` Balbir Singh
2018-03-09 15:54 ` Torsten Duwe
2017-12-12 14:05 ` [PATCH] On ppc64le we HAVE_RELIABLE_STACKTRACE Josh Poimboeuf
2017-12-15 9:40 ` Nicholas Piggin
2017-12-18 2:58 ` Josh Poimboeuf [this message]
2017-12-18 3:39 ` Balbir Singh
2017-12-18 4:01 ` Josh Poimboeuf
2017-12-18 5:33 ` Nicholas Piggin
2017-12-18 18:56 ` Josh Poimboeuf
2017-12-19 2:46 ` Nicholas Piggin
2017-12-19 11:28 ` Torsten Duwe
2017-12-19 21:46 ` Josh Poimboeuf
2017-12-21 12:10 ` Michael Ellerman
2017-12-23 4:00 ` Josh Poimboeuf
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