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

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Date:   Mon, 4 Nov 2019 12:56:39 +0000
From:   Will Deacon <will@...nel.org>
To:     Amit Daniel Kachhap <amit.kachhap@....com>
Cc:     Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        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, svens@...ckframe.org,
        takahiro.akashi@...aro.org
Subject: Re: [PATCHv2 0/8] arm64: ftrace cleanup + FTRACE_WITH_REGS

On Sat, Nov 02, 2019 at 05:42:25PM +0530, Amit Daniel Kachhap wrote:
> On 10/29/19 10:28 PM, Mark Rutland wrote:
> > 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.
> I tested the whole series with my latest in-kernel ptrauth patches [1]
> and graph_tracer/function_graph_tracer works fine, So for the whole series,
> Tested-by: Amit Daniel Kachhap <amit.kachhap@....com>
> 
> Also I gave few minor comments in the individual patches. With those
> comments,
> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@....com>

I don't think this means what you think it means. Please read:

Documentation/process/submitting-patches.rst

Will