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Subject: Re: [PATCH v7 2/2] ARM: ftrace: Add MODULE_PLTS support
To:     Qais Yousef <qais.yousef@arm.com>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Russell King <linux@armlinux.org.uk>,
        linux-arm-kernel@lists.infradead.org,
        Florian Fainelli <f.fainelli@gmail.com>,
        linux-kernel@vger.kernel.org,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>
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From:   Alexander Sverdlin <alexander.sverdlin@nokia.com>
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Date:   Wed, 10 Mar 2021 08:23:30 +0100
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Hi!

On 09/03/2021 18:42, Qais Yousef wrote:
>>> I tried on 5.12-rc2 and 5.11 but couldn't reproduce the problem using your
> I still can't reproduce on 5.12-rc2.
> 
> I do have CONFIG_ARM_MODULE_PLTS=y. Do you need to do something else after
> loading the module? I tried starting ftrace, but maybe there's a particular
> combination required?

You need to load a BIG module, so big that it has no place in the modules area
any more and goes to vmalloc area.

>>> instructions on the other email. But most likely because I'm hitting another
>>> problem that could be masking it. I'm not sure it is related or just randomly
>>> happened to hit it.
>>>
>>> Did you see something similar?
>> [...]
>>
>>> 	[    0.000000] [<c1b01a38>] (ftrace_bug) from [<c046316c>] (ftrace_process_locs+0x2b0/0x518)
>>> 	[    0.000000]  r7:c3817ac4 r6:c38040c0 r5:00000a3c r4:000134e4
>>> 	[    0.000000] [<c0462ebc>] (ftrace_process_locs) from [<c2b25240>] (ftrace_init+0xc8/0x174)
>>> 	[    0.000000]  r10:c2ffa000 r9:c2be8a78 r8:c2c5d1fc r7:c2c0c208 r6:00000001 r5:c2d0908c
>>> 	[    0.000000]  r4:c362f518
>>> 	[    0.000000] [<c2b25178>] (ftrace_init) from [<c2b00e14>] (start_kernel+0x2f4/0x5b8)
>>> 	[    0.000000]  r9:c2be8a78 r8:dbfffec0 r7:00000000 r6:c36385cc r5:c2d08f00 r4:c2ffa000
>>> 	[    0.000000] [<c2b00b20>] (start_kernel) from [<00000000>] (0x0)
>> This means, FTRACE has more problems with your kernel/compiler/platform, I've addressed similar issue
>> in the past, but my patch should be long merged:
>>
>> https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1817963.html
>>
>> Could it be the same problem as here:
>> https://www.spinics.net/lists/arm-kernel/msg854022.html
>>
>> Seems that the size check deserves something line BUILD_BUG_ON() with FTRACE...
> So I only see this when I convert all modules to be built-in
> 
> 	sed -i 's/=m/=y/' .config
> 
> FWIW, I see the problem with your patch applied too. Trying to dig more into
> it..

Then it's definitely the problem explained in the second link. If you have THUMB2 kernel, maybe
you have to switch to ARM.

-- 
Best regards,
Alexander Sverdlin.