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Subject: Re: [PATCH v7 0/2] ARM: Implement MODULE_PLT support in FTRACE
To:     Linus Walleij <linus.walleij@linaro.org>,
        Ard Biesheuvel <ardb@kernel.org>
Cc:     Florian Fainelli <f.fainelli@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Russell King <linux@armlinux.org.uk>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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From:   Alexander Sverdlin <alexander.sverdlin@nokia.com>
Message-ID: <950ee6f5-13f2-8a07-6956-6921df4fc435@nokia.com>
Date:   Tue, 2 Mar 2021 11:00:51 +0100
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Hello Linus,

On 02/03/2021 09:29, Linus Walleij wrote:
>>>> 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

First of all:

config ARM_MODULE_PLTS                                                                                                                                                                                             
        bool "Use PLTs to allow module memory to spill over into vmalloc area"                                                                                                                                     


[...]

> Any suggestions on a quick use case that illustrates how the problem
> manifest and how to test it is gone? The errors in patch 2, what do
> I need to configure in to get them? Does it manifest at modprobe?

And then I use this module to test for the problem:

/**********************************************************************
 * Author: Alexander Sverdlin <alexander.sverdlin@nokia.com>
 *
 * Copyright (c) 2018 Nokia
 *
 * SPDX-License-Identifier: GPL-2.0
 *
 * This module is intended to test ARM MODULE_PLT functionality
 **********************************************************************/

#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/module.h>

static int fatmod_init(void)
{
	asm volatile (".rept (6 * 1024 * 1024 / 2)\n\t"
		      "nop\n\t"
		      ".endr");
	return 0;
}
module_init(fatmod_init);

static void __exit fatmod_exit(void)
{
}
module_exit(fatmod_exit);

MODULE_AUTHOR("Alexander Sverdlin <alexander.sverdlin@nokia.com>");
MODULE_DESCRIPTION("ARM MODULE_PLT test module");
MODULE_LICENSE("GPL");

-- 
Best regards,
Alexander Sverdlin.