linux-kernel - Re: [PATCHv2 0/8] arm64: ftrace cleanup + FTRACE_WITH

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Date:   Fri, 1 Nov 2019 16:39:30 +0100
From:   Sven Schnelle <svens@...ckframe.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        amit.kachhap@....com, catalin.marinas@....com, deller@....de,
        duwe@...e.de, James.Bottomley@...senPartnership.com,
        james.morse@....com, jeyu@...nel.org, jpoimboe@...hat.com,
        jthierry@...hat.com, linux-parisc@...r.kernel.org,
        mingo@...hat.com, peterz@...radead.org, rostedt@...dmis.org,
        takahiro.akashi@...aro.org, will@...nel.org
Subject: Re: [PATCHv2 0/8] arm64: ftrace cleanup + FTRACE_WITH_REGS

Hi Mark,

On Tue, Oct 29, 2019 at 04:58:24PM +0000, Mark Rutland wrote:
> Hi,
> 
> This series is a reworked version of Torsten's FTRACE_WITH_REGS series
> [1]. I've tried to rework the existing code in preparatory patches so
> that the patchable-function-entry bits slot in with fewer surprises.
> This version is based on v5.4-rc3, and can be found in my
> arm64/ftrace-with-regs branch [2].
> 
> Patch 1 adds an (optional) ftrace_init_nop(), which the core code uses
> to initialize callsites. This allows us to avoid a synthetic MCOUNT_ADDR
> symbol, and more cleanly separates the one-time initialization of the
> callsite from dynamic NOP<->CALL modification. Architectures which don't
> implement this get the existing ftrace_make_nop() with MCOUNT_ADDR.
> 
> Recently parisc gained ftrace support using patchable-function-entry.
> Patch 2 makes the handling of module callsite locations common in
> kernel/module.c with a new FTRACE_CALLSITE_SECTION definition, and
> removed the newly redundant bits from arch/parisc.
> 
> Patches 3 and 4 move the module PLT initialization to module load time,
> which simplifies runtime callsite modification. This also means that we
> don't transitently mark the module text RW, and will allow for the
> removal of module_disable_ro().
> 
> Patches 5 and 6 add some trivial infrastructure, with patch 7 finally
> adding FTRACE_WITH_REGS support. Additional work will be required for
> livepatching (e.g. implementing reliable stack trace), which is
> commented as part of patch 7.
> 
> Patch 8 is a trivial cleanup atop of the rest of the series, making the
> code easier to read and less susceptible to config-specific breakage.
> 
> Since v1 [3]:
> * Add a couple of people to Cc
> * Fold in Ard's Reviewed-by tag
> * Rename ftrace_code_init_disabled() to ftrace_nop_initialize()
> * Move ftrace_init_nop() to <linux/ftrace.h>, with kerneldoc
> * Update kerneldoc for rec parameters
[..]

I tested this series on parisc both with ftracing kernel internal functions and
module functions. Both are working fine, so feel free to add my

Tested-by: Sven Schnelle <svens@...ckframe.org>

Regards
Sven