linux-kernel - Re: [PATCH v7 0/2] ARM: Implement MODULE

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Message-ID: <a5c1e655-cdbc-18d5-55fd-c1690c31acbe@gmail.com>
Date:   Wed, 3 Feb 2021 10:23:36 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Alexander A Sverdlin <alexander.sverdlin@...ia.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [PATCH v7 0/2] ARM: Implement MODULE_PLT support in FTRACE

On 1/27/21 3:09 AM, Alexander A Sverdlin wrote:
> From: Alexander Sverdlin <alexander.sverdlin@...ia.com>
> 
> FTRACE's function tracer currently doesn't always work on ARM with
> MODULE_PLT option enabled. If the module is loaded too far, FTRACE's
> code modifier cannot cope with introduced veneers and turns the
> function tracer off globally.
> 
> ARM64 already has a solution for the problem, refer to the following
> patches:
> 
> arm64: ftrace: emit ftrace-mod.o contents through code
> arm64: module-plts: factor out PLT generation code for ftrace
> arm64: ftrace: fix !CONFIG_ARM64_MODULE_PLTS kernels
> arm64: ftrace: fix building without CONFIG_MODULES
> arm64: ftrace: add support for far branches to dynamic ftrace
> arm64: ftrace: don't validate branch via PLT in ftrace_make_nop()
> 
> But the presented ARM variant has just a half of the footprint in terms of
> the changed LoCs. It also retains the code validation-before-modification
> instead of switching it off.

Ard, Russell should this be sent to the patch tracker?
-- 
Florian