linux-kernel - Re: [RFC PATCH v2 3/4] arm64: Detect FTRACE cases that make the stack trace unreliable

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Message-ID: <20210408165825.GP4516@sirena.org.uk>
Date:   Thu, 8 Apr 2021 17:58:25 +0100
From:   Mark Brown <broonie@...nel.org>
To:     madvenka@...ux.microsoft.com, mark.rutland@....com
Cc:     jpoimboe@...hat.com, jthierry@...hat.com, catalin.marinas@....com,
        will@...nel.org, linux-arm-kernel@...ts.infradead.org,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 3/4] arm64: Detect FTRACE cases that make the
 stack trace unreliable

On Mon, Apr 05, 2021 at 03:43:12PM -0500, madvenka@...ux.microsoft.com wrote:
> From: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
> 
> When CONFIG_DYNAMIC_FTRACE_WITH_REGS is enabled and tracing is activated
> for a function, the ftrace infrastructure is called for the function at
> the very beginning. Ftrace creates two frames:

This looks good to me however I'd really like someone who has a firmer
understanding of what ftrace is doing to double check as it is entirely
likely that I am missing cases here, it seems likely that if I am
missing stuff it's extra stuff that needs to be added and we're not
actually making use of the reliability information yet.

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