netdev - Re: [PATCH 4.19 5/6] ARM: 8788/1: ftrace: remove old mcount support

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Date:   Tue, 11 Jan 2022 21:58:42 +0100
From:   Stefan Agner <stefan@...er.ch>
To:     Greg KH <greg@...ah.com>
Cc:     Anders Roxell <anders.roxell@...aro.org>, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org, woojung.huh@...rochip.com,
        UNGLinuxDriver@...rochip.com, davem@...emloft.net,
        netdev@...r.kernel.org, linux-usb@...r.kernel.org,
        clang-built-linux@...glegroups.com, ulli.kroll@...glemail.com,
        linux@...linux.org.uk, linux-arm-kernel@...ts.infradead.org,
        amitkarwar@...il.com, nishants@...vell.com, gbhat@...vell.com,
        huxinming820@...il.com, kvalo@...eaurora.org,
        linux-wireless@...r.kernel.org, rostedt@...dmis.org,
        mingo@...hat.com, dmitry.torokhov@...il.com,
        ndesaulniers@...gle.com, nathan@...nel.org,
        linux-input@...r.kernel.org,
        Russell King <rmk+kernel@...linux.org.uk>
Subject: Re: [PATCH 4.19 5/6] ARM: 8788/1: ftrace: remove old mcount support

On 2021-12-20 11:57, Greg KH wrote:
> On Fri, Dec 17, 2021 at 03:41:18PM +0100, Anders Roxell wrote:
>> From: Stefan Agner <stefan@...er.ch>
>>
>> commit d3c61619568c88d48eccd5e74b4f84faa1440652 upstream.
>>
>> Commit cafa0010cd51 ("Raise the minimum required gcc version to 4.6")
>> raised the minimum GCC version to 4.6. Old mcount is only required for
>> GCC versions older than 4.4.0. Hence old mcount support can be dropped
>> too.
>>
>> Signed-off-by: Stefan Agner <stefan@...er.ch>
>> Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>
>> Signed-off-by: Anders Roxell <anders.roxell@...aro.org>
> 
> Why is this needed for clang builds in 4.19?

As far as I remember, Clang tripped over this part:

-#ifndef CONFIG_OLD_MCOUNT
-#if (__GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 4))
-#error Ftrace requires CONFIG_FRAME_POINTER=y with GCC older than
4.4.0.
-#endif
-#endif

Since mcount support wasn't required upstream at that point, instead of
fixing it for Clang I just removed it.

--
Stefan