linux-kernel - Re: ld.lld: error: relocation R_RISCV_HI20 cannot be used against symbol 'misaligned_access

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Date:   Tue, 20 Jun 2023 09:05:19 +0200
From:   Alexandre Ghiti <alexghiti@...osinc.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     kernel test robot <lkp@...el.com>, llvm@...ts.linux.dev,
        oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Palmer Dabbelt <palmer@...osinc.com>
Subject: Re: ld.lld: error: relocation R_RISCV_HI20 cannot be used against
 symbol 'misaligned_access_speed'; recompile with -fPIC

On Wed, Jun 14, 2023 at 6:40 PM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Tue, Jun 13, 2023 at 4:17 AM Alexandre Ghiti <alexghiti@...osinc.com> wrote:
> >
> > On Sun, Jun 11, 2023 at 2:11 AM kernel test robot <lkp@...el.com> wrote:
> > >
> > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > > head:   022ce8862dff83c859089cd14bc4dca0733e2f90
> > > commit: 8dc2a7e8027fbeca0c7df81d4c82e735a59b5741 riscv: Fix relocatable kernels with early alternatives using -fno-pie
> > > date:   10 days ago
> > > config: riscv-randconfig-r022-20230611 (https://download.01.org/0day-ci/archive/20230611/202306110855.7TlBCIzI-lkp@intel.com/config)
> > > compiler: clang version 16.0.4 (https://github.com/llvm/llvm-project.git ae42196bc493ffe877a7e3dff8be32035dea4d07)
> > > reproduce (this is a W=1 build):
> > >         mkdir -p ~/bin
> > >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> > >         chmod +x ~/bin/make.cross
> > >         # install riscv cross compiling tool for clang build
> > >         # apt-get install binutils-riscv64-linux-gnu
> > >         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8dc2a7e8027fbeca0c7df81d4c82e735a59b5741
> > >         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> > >         git fetch --no-tags linus master
> > >         git checkout 8dc2a7e8027fbeca0c7df81d4c82e735a59b5741
> > >         # save the config file
> > >         mkdir build_dir && cp config build_dir/.config
> > >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang ~/bin/make.cross W=1 O=build_dir ARCH=riscv olddefconfig
> > >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang ~/bin/make.cross W=1 O=build_dir ARCH=riscv SHELL=/bin/bash
> > >
> > > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > > the same patch/commit), kindly add following tags
> > > | Reported-by: kernel test robot <lkp@...el.com>
> > > | Closes: https://lore.kernel.org/oe-kbuild-all/202306110855.7TlBCIzI-lkp@intel.com/
> > >
> > > All errors (new ones prefixed by >>):
> > >
> > > >> ld.lld: error: relocation R_RISCV_HI20 cannot be used against symbol 'misaligned_access_speed'; recompile with -fPIC
> > >    >>> defined in vmlinux.a(arch/riscv/kernel/cpufeature.o)
> > >    >>> referenced by errata.c:42 (arch/riscv/errata/thead/errata.c:42)
> > >    >>>               arch/riscv/errata/thead/errata.o:(thead_feature_probe_func) in archive vmlinux.a
> > > --
> > > >> ld.lld: error: relocation R_RISCV_LO12_I cannot be used against symbol 'misaligned_access_speed'; recompile with -fPIC
> > >    >>> defined in vmlinux.a(arch/riscv/kernel/cpufeature.o)
> > >    >>> referenced by errata.c:42 (arch/riscv/errata/thead/errata.c:42)
> > >    >>>               arch/riscv/errata/thead/errata.o:(thead_feature_probe_func) in archive vmlinux.a
> > > --
> > > >> ld.lld: error: relocation R_RISCV_HI20 cannot be used against symbol 'riscv_cbom_block_size'; recompile with -fPIC
> > >    >>> defined in vmlinux.a(arch/riscv/mm/cacheflush.o)
> > >    >>> referenced by errata.c:42 (arch/riscv/errata/thead/errata.c:42)
> > >    >>>               arch/riscv/errata/thead/errata.o:(thead_errata_patch_func) in archive vmlinux.a
> > > --
> > > >> ld.lld: error: relocation R_RISCV_LO12_S cannot be used against symbol 'riscv_cbom_block_size'; recompile with -fPIC
> > >    >>> defined in vmlinux.a(arch/riscv/mm/cacheflush.o)
> > >    >>> referenced by errata.c:42 (arch/riscv/errata/thead/errata.c:42)
> > >    >>>               arch/riscv/errata/thead/errata.o:(thead_errata_patch_func) in archive vmlinux.a
> > > --
> > > >> ld.lld: error: relocation R_RISCV_HI20 cannot be used against symbol '__per_cpu_offset'; recompile with -fPIC
> > >    >>> defined in vmlinux.a(mm/percpu.o)
> > >    >>> referenced by errata.c:42 (arch/riscv/errata/thead/errata.c:42)
> > >    >>>               arch/riscv/errata/thead/errata.o:(thead_feature_probe_func) in archive vmlinux.a
> > > --
> > > >> ld.lld: error: relocation R_RISCV_LO12_I cannot be used against symbol '__per_cpu_offset'; recompile with -fPIC
> > >    >>> defined in vmlinux.a(mm/percpu.o)
> > >    >>> referenced by errata.c:42 (arch/riscv/errata/thead/errata.c:42)
> > >    >>>               arch/riscv/errata/thead/errata.o:(thead_feature_probe_func) in archive vmlinux.a
> > >
> >
> > So I looked into those errors, the config is basically = RELOCATABLE +
> > MEDLOW - EARLY_ALTERNATIVES. Then errata/thead is not compiled as
>
> Thanks for taking a look.  Shouldn't CONFIG_RELOCATABLE be setting
> -fPIC? If so, why is LLD complaining about -fPIC not being used?
>
> arch/riscv/Makefile sets -fPIE if CONFIG_RELOCATABLE == y.
>
> Is it possible that -fpie was dropped for these object files, or
> -fno-pic or -fno-pie was added to the cflags for these object files
> somehow?

There was a runtime issue where I had to drop the -fPIE for those
files because some part *may* be executed before the MMU is enabled,
so any access to a global symbol through the GOT needs a relocation
which is "done" only virtually.

commit 8dc2a7e8027f ("riscv: Fix relocatable kernels with early
alternatives using -fno-pie") added the -fno-pie flag, but not the
medany because the medany is correctly set in errata/thead/Makefile
only when EARLY_ALTERNATIVES is set.

So to me we do not need the medany flag if !EARLY_ALTERNATIVES since
the code is not executed with MMU off and then medlow should work.


>
> I've filed
> https://github.com/ClangBuiltLinux/linux/issues/1872
> to track this.
>
> > medany, which makes sense since we only need this code to be medany
> > when EARLY_ALTERNATIVES is enabled (because the code would be executed
> > with mmu off, which is not the case here).
> >
> > I can fix those errors by adding the medany flag, but I'm not sure
> > actually we want to do that since we do not need it and gcc does not
> > complain: any idea?
> >
> > Alex
> >
> >
> >
> > > --
> > > 0-DAY CI Kernel Test Service
> > > https://github.com/intel/lkp-tests/wiki
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers