From: Petr Mladek <pmladek@suse.com>
To: Abel Vesa <abelvesa@gmail.com>
Cc: Abel Vesa <abelvesa@linux.com>,
linux@armlinux.org.uk, rostedt@goodmis.org, mingo@redhat.com,
viro@zeniv.linux.org.uk, jjhiblot@traphandler.com,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, robin.murphy@arm.com,
zhouchengming1@huawei.com
Subject: Re: [PATCH] arm: ftrace: Adds support for CONFIG_DYNAMIC_FTRACE_WITH_REGS
Date: Tue, 10 Jan 2017 16:51:12 +0100 [thread overview]
Message-ID: <20170110155112.GB14894@pathway.suse.cz> (raw)
In-Reply-To: <20161208224655.GA6319@gce>
On Thu 2016-12-08 22:46:55, Abel Vesa wrote:
> On Thu, Dec 08, 2016 at 09:46:35PM +0000, Abel Vesa wrote:
> > From: Jean-Jacques Hiblot <jjhiblot@traphandler.com>
> >
> > From: Jean-Jacques Hiblot <jjhiblot@traphandler.com>
>
> >From statement twice in the commit message. Will resend.
> >
> > The DYNAMIC_FTRACE_WITH_REGS configuration makes it possible for a ftrace
> > operation to specify if registers need to saved/restored by the ftrace handler.
> > This is needed by kgraft and possibly other ftrace-based tools, and the ARM
> > architecture is currently lacking this feature. It would also be the first step
> > to support the "Kprobes-on-ftrace" optimization on ARM.
> >
> > This patch introduces a new ftrace handler that stores the registers on the
> > stack before calling the next stage. The registers are restored from the stack
> > before going back to the instrumented function.
> >
> > A side-effect of this patch is to activate the support for ftrace_modify_call()
> > as it defines ARCH_SUPPORTS_FTRACE_OPS for the ARM architecture
> >
> > Signed-off-by: Jean-Jacques Hiblot <jjhiblot@traphandler.com>
> > Signed-off-by: Abel Vesa <abelvesa@linux.com>
> > ---
> > arch/arm/Kconfig | 2 ++
> > arch/arm/include/asm/ftrace.h | 4 +++
> > arch/arm/kernel/entry-ftrace.S | 78 ++++++++++++++++++++++++++++++++++++++++++
> > arch/arm/kernel/ftrace.c | 33 ++++++++++++++++++
> > 4 files changed, 117 insertions(+)
> >
> > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > index b5d529f..87f1a9f 100644
> > --- a/arch/arm/Kconfig
> > +++ b/arch/arm/Kconfig
> > @@ -50,6 +50,7 @@ config ARM
> > select HAVE_DMA_API_DEBUG
> > select HAVE_DMA_CONTIGUOUS if MMU
> > select HAVE_DYNAMIC_FTRACE if (!XIP_KERNEL) && !CPU_ENDIAN_BE32 && MMU
> > + select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
> > select HAVE_EFFICIENT_UNALIGNED_ACCESS if (CPU_V6 || CPU_V6K || CPU_V7) && MMU
> > select HAVE_EXIT_THREAD
> > select HAVE_FTRACE_MCOUNT_RECORD if (!XIP_KERNEL)
> > @@ -90,6 +91,7 @@ config ARM
> > select PERF_USE_VMALLOC
> > select RTC_LIB
> > select SYS_SUPPORTS_APM_EMULATION
> > + select FRAME_POINTER if DYNAMIC_FTRACE_WITH_REGS && FUNCTION_GRAPH_TRACER
FRAME_POINTER is not for free. It takes space on the stack. Also there
is a performance penalty. Do we really need to depend on it? If so,
it might be worth a note in the commit message.
I made only a quick look at the patch. It looks reasonable. But I do
not have enough knowledge about the arm architecture, assembly, and
ftrace-specifics. Also I cannot test it easily. So issues might
be hidden to my eyes.
Best Regards,
Petr
next prev parent reply other threads:[~2017-01-10 15:51 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-08 21:46 [PATCH] arm: ftrace: Adds support for CONFIG_DYNAMIC_FTRACE_WITH_REGS Abel Vesa
2016-12-08 22:46 ` Abel Vesa
2017-01-10 15:51 ` Petr Mladek [this message]
2017-01-12 0:19 ` Abel Vesa
2017-01-12 14:30 ` Jean-Jacques Hiblot
2017-01-13 8:30 ` Jean-Jacques Hiblot
2017-01-24 0:43 ` Abel Vesa
2016-12-08 22:49 Abel Vesa
2017-05-12 20:38 abelvesa
2017-05-12 21:05 ` Abel Vesa
2017-05-12 21:06 Abel Vesa
2017-05-23 19:53 ` Russell King - ARM Linux
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