linux-kernel - Re: undefined reference to `__aeabi_uldivmod' after 25c13324d03d ("IB/mlx5: Add steering SW ICM device memory type")

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Date:   Wed, 15 May 2019 08:31:49 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Leon Romanovsky <leonro@...lanox.com>
Cc:     Jason Gunthorpe <jgg@...pe.ca>,
        Nathan Chancellor <natechancellor@...il.com>,
        "fengguang.wu@...el.com" <fengguang.wu@...el.com>,
        "kbuild@...org" <kbuild@...org>,
        Ariel Levkovich <lariel@...lanox.com>,
        Eli Cohen <eli@...lanox.com>, Mark Bloch <markb@...lanox.com>,
        Doug Ledford <dledford@...hat.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: undefined reference to `__aeabi_uldivmod' after 25c13324d03d
 ("IB/mlx5: Add steering SW ICM device memory type")

On Wed, May 15, 2019 at 7:04 AM Leon Romanovsky <leonro@...lanox.com> wrote:
> On Tue, May 14, 2019 at 09:32:02PM -0300, Jason Gunthorpe wrote:
> > On Tue, May 14, 2019 at 12:45:10PM -0700, Nathan Chancellor wrote:
> > > Hi all,
> > >
> > > I checked the RDMA mailing list and trees and I haven't seen this
> > > reported/fixed yet (forgive me if it has) but when building for arm32
> > > with multi_v7_defconfig and the following configs (distilled from
> > > allyesconfig):
> > >
> > > CONFIG_INFINIBAND=y
> > > CONFIG_INFINIBAND_ON_DEMAND_PAGING=y
> > > CONFIG_INFINIBAND_USER_ACCESS=y
> > > CONFIG_MLX5_CORE=y
> > > CONFIG_MLX5_INFINIBAND=y
> > >
> > > The following link time errors occur:
> > >
> > > arm-linux-gnueabi-ld: drivers/infiniband/hw/mlx5/main.o: in function `mlx5_ib_alloc_dm':
> > > main.c:(.text+0x60c): undefined reference to `__aeabi_uldivmod'
> > > arm-linux-gnueabi-ld: drivers/infiniband/hw/mlx5/cmd.o: in function `mlx5_cmd_alloc_sw_icm':
> > > cmd.c:(.text+0x6d4): undefined reference to `__aeabi_uldivmod'
> > > arm-linux-gnueabi-ld: drivers/infiniband/hw/mlx5/cmd.o: in function `mlx5_cmd_dealloc_sw_icm':
> > > cmd.c:(.text+0x9ec): undefined reference to `__aeabi_uldivmod'
> >
> > Fengguang, I'm surprised that 0-day didn't report this earlier..
>
> I got many successful emails after I pushed this patch to 0-day testing.

The long division warnings can compiler specific, and depend on certain
optimization options, as compilers can optimize out certain divisions and
replace them with multiplications and/or shifts, or prove that they can be
replaced with a 32-bit division. If this is a case that gcc manages to
optimize but clang does not, it might be worth looking into whether an
optimization can be added to clang, in addition to improving the source.

     Arnd