From: Torsten Duwe <duwe@lst.de>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Jiri Kosina <jkosina@suse.cz>, Miroslav Benes <mbenes@suse.cz>,
Petr Mladek <pmladek@suse.com>, Jessica Yu <jeyu@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>,
linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
live-patching@vger.kernel.org
Subject: Re: [PATCH v8 1/8] ppc64 (le): prepare for -mprofile-kernel
Date: Wed, 17 Feb 2016 12:30:22 +0100 [thread overview]
Message-ID: <20160217113022.GA9578@lst.de> (raw)
In-Reply-To: <1455706540.4450.2.camel@ellerman.id.au>
On Wed, Feb 17, 2016 at 09:55:40PM +1100, Michael Ellerman wrote:
> On Wed, 2016-02-10 at 17:21 +0100, Torsten Duwe wrote:
>
> > --- a/arch/powerpc/kernel/module_64.c
> > +++ b/arch/powerpc/kernel/module_64.c
> > @@ -476,17 +474,44 @@ static unsigned long stub_for_addr(Elf64_Shdr *sechdrs,
> > return (unsigned long)&stubs[i];
> > }
> >
> > +#ifdef CC_USING_MPROFILE_KERNEL
> > +static int is_early_mcount_callsite(u32 *instruction)
> > +{
> > + /* -mprofile-kernel sequence starting with
> > + * mflr r0 and maybe std r0, LRSAVE(r1).
> > + */
> > + if ((instruction[-3] == PPC_INST_MFLR &&
> > + instruction[-2] == PPC_INST_STD_LR) ||
> > + instruction[-2] == PPC_INST_MFLR) {
> > + /* Nothing to be done here, it's an _mcount
> > + * call location and r2 will have to be
> > + * restored in the _mcount function.
> > + */
> > + return 1;
> > + }
> > + return 0;
> > +}
>
> On a kernel built with the 2 instruction version this will fault when the
> function we're looking at is located at the beginning of a page. Because
> instruction[-3] goes off the front of the mapping.
>
> We can probably fix that. But it's still a bit dicey.
Not necessarily. Now that it's a separate function, it can be nested a bit deeper,
so we don't take chances on compiler optimisation:
if (instruction[-2] == PPC_INST_STD_LR) /* where should R0 come from? there must be... */
{
if (instruction[-3] == PPC_INST_MFLR)
return 1;
}
else if (instruction[-2] == PPC_INST_MFLR)
return 1;
return 0;
> I'm wondering if we want to just say we only support the 2 instruction version.
> Currently that means GCC 6 only, or a distro compiler with the backport of
> e95d0248dace. But we could also ask GCC to backport it to 4.9 and 5.
>
> Thoughts?
IMHO that's a too weak reason for a too strong limitation. OTOH getting everyone
to use the 2 insn version sounds appealing...
Is e95d0248dace self-sufficient or does it depend on other improvements?
Torsten
next prev parent reply other threads:[~2016-02-17 11:30 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-10 17:29 [PATCH v8 0/8] ftrace with regs + live patching for ppc64 LE (ABI v2) Torsten Duwe
2016-01-28 15:32 ` [PATCH v8 8/8] livepatch: Detect offset for the ftrace location during build Torsten Duwe
2016-02-12 16:13 ` Balbir Singh
2016-02-12 16:45 ` Petr Mladek
2016-02-13 1:33 ` Balbir Singh
2016-02-16 5:47 ` Kamalesh Babulal
2016-02-16 8:23 ` Torsten Duwe
2016-02-16 10:30 ` Kamalesh Babulal
2016-02-16 10:39 ` Torsten Duwe
2016-02-16 13:57 ` Petr Mladek
2016-02-17 3:08 ` Michael Ellerman
2016-02-23 17:00 ` Torsten Duwe
2016-02-24 6:37 ` Balbir Singh
2016-02-24 6:55 ` Balbir Singh
2016-02-24 9:23 ` Torsten Duwe
2016-02-24 11:22 ` Balbir Singh
2016-02-24 7:51 ` Kamalesh Babulal
2016-02-10 16:21 ` [PATCH v8 1/8] ppc64 (le): prepare for -mprofile-kernel Torsten Duwe
2016-02-17 10:55 ` Michael Ellerman
2016-02-17 11:30 ` Torsten Duwe [this message]
2016-02-17 11:39 ` Michael Ellerman
2016-02-10 16:22 ` [PATCH v8 2/8] ppc64le FTRACE_WITH_REGS implementation Torsten Duwe
2016-02-10 16:22 ` [PATCH v8 3/8] ppc use ftrace_modify_all_code default Torsten Duwe
2016-02-10 16:25 ` [PATCH v8 4/8] ppc64 ftrace_with_regs configuration variables Torsten Duwe
2016-02-11 7:48 ` Balbir Singh
2016-02-11 8:39 ` Kamalesh Babulal
2016-02-11 9:35 ` Balbir Singh
2016-02-11 13:00 ` Murali Sampath
2016-02-11 13:00 ` Murali Sampath
2016-02-11 8:42 ` Torsten Duwe
2016-02-11 9:34 ` Balbir Singh
2016-02-15 10:27 ` Michael Ellerman
2016-02-15 12:56 ` Jiri Kosina
2016-02-15 14:04 ` Torsten Duwe
2016-02-15 22:21 ` Torsten Duwe
2016-02-16 4:53 ` Balbir Singh
2016-02-16 10:09 ` Michael Ellerman
2016-02-16 10:35 ` Torsten Duwe
2016-02-10 16:27 ` [PATCH v8 5/8] ppc64 ftrace_with_regs: disable profiling for some files Torsten Duwe
2016-02-10 16:34 ` [PATCH v8 6/8] Implement kernel live patching for ppc64le (ABIv2) Torsten Duwe
2016-02-11 9:01 ` Miroslav Benes
2016-02-10 16:36 ` [PATCH v8 7/8] Enable LIVEPATCH to be configured on ppc64le and add livepatch.o if it is selected Torsten Duwe
2016-02-11 6:18 ` [PATCH v8 0/8] ftrace with regs + live patching for ppc64 LE (ABI v2) Balbir Singh
2016-02-11 8:38 ` Torsten Duwe
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