netdev - Re: [PATCH] ptp_qoriq: fix overflow in ptp_qoriq

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Message-ID: <CA+G9fYuwh0QF7PwdYW9-QEGE909-a5y5Xqh7ki=ppUyDDHtyQA@mail.gmail.com>
Date:   Thu, 25 Mar 2021 22:02:43 +0530
From:   Naresh Kamboju <naresh.kamboju@...aro.org>
To:     Yangbo Lu <yangbo.lu@....com>
Cc:     Netdev <netdev@...r.kernel.org>,
        Richard Cochran <richardcochran@...il.com>
Subject: Re: [PATCH] ptp_qoriq: fix overflow in ptp_qoriq_adjfine() u64 calcalation

FYI,

On Tue, 23 Mar 2021 at 13:26, Yangbo Lu <yangbo.lu@....com> wrote:
>
> Current calculation for diff of TMR_ADD register value may have
> 64-bit overflow in this code line, when long type scaled_ppm is
> large.
>
> adj *= scaled_ppm;
>
> This patch is to resolve it by using mul_u64_u64_div_u64().
>
> Signed-off-by: Yangbo Lu <yangbo.lu@....com>
> ---
>  drivers/ptp/ptp_qoriq.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/ptp/ptp_qoriq.c b/drivers/ptp/ptp_qoriq.c
> index 68beb1bd07c0..f7f220700cb5 100644
> --- a/drivers/ptp/ptp_qoriq.c
> +++ b/drivers/ptp/ptp_qoriq.c
> @@ -189,15 +189,16 @@ int ptp_qoriq_adjfine(struct ptp_clock_info *ptp, long scaled_ppm)
>         tmr_add = ptp_qoriq->tmr_add;
>         adj = tmr_add;
>
> -       /* calculate diff as adj*(scaled_ppm/65536)/1000000
> -        * and round() to the nearest integer
> +       /*
> +        * Calculate diff and round() to the nearest integer
> +        *
> +        * diff = adj * (ppb / 1000000000)
> +        *      = adj * scaled_ppm / 65536000000
>          */
> -       adj *= scaled_ppm;
> -       diff = div_u64(adj, 8000000);
> -       diff = (diff >> 13) + ((diff >> 12) & 1);
> +       diff = mul_u64_u64_div_u64(adj, scaled_ppm, 32768000000);

While building Linux next 20210325 tag for powerpc architecture ppc6xx_defconfig
failed due to following warnings / errors.

 - powerpc (ppc6xx_defconfig) with gcc-8
 - powerpc (ppc6xx_defconfig) with gcc-9
 - powerpc (ppc6xx_defconfig) with gcc-10

make --silent --keep-going --jobs=8
O=/home/tuxbuild/.cache/tuxmake/builds/1/tmp ARCH=powerpc
CROSS_COMPILE=powerpc64le-linux-gnu- 'CC=sccache
powerpc64le-linux-gnu-gcc' 'HOSTCC=sccache gcc'

INFO: Uncompressed kernel (size 0xd985ec) overlaps the address of the
wrapper(0x400000)
INFO: Fixing the link_address of wrapper to (0xe00000)
INFO: Uncompressed kernel (size 0xd985ec) overlaps the address of the
wrapper(0x400000)
INFO: Fixing the link_address of wrapper to (0xe00000)
INFO: Uncompressed kernel (size 0xd985ec) overlaps the address of the
wrapper(0x400000)
INFO: Fixing the link_address of wrapper to (0xe00000)
ERROR: modpost: "mul_u64_u64_div_u64" [drivers/ptp/ptp-qoriq.ko] undefined!

Reported-by: Naresh Kamboju <naresh.kamboju@...aro.org>

Steps to reproduce:
-------------------
# TuxMake is a command line tool and Python library that provides
# portable and repeatable Linux kernel builds across a variety of
# architectures, toolchains, kernel configurations, and make targets.
#
# TuxMake supports the concept of runtimes.
# See https://docs.tuxmake.org/runtimes/, for that to work it requires
# that you install podman or docker on your system.
#
# To install tuxmake on your system globally:
# sudo pip3 install -U tuxmake
#
# See https://docs.tuxmake.org/ for complete documentation.


tuxmake --runtime podman --target-arch powerpc --toolchain gcc-8
--kconfig ppc6xx_defconfig

-- 
Linaro LKFT
https://lkft.linaro.org