Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 1 Sep 2020 22:21:23 -0700
From:   Nathan Chancellor <natechancellor@gmail.com>
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        Nicholas Piggin <npiggin@gmail.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Joe Lawrence <joe.lawrence@redhat.com>,
        Christophe Leroy <christophe.leroy@c-s.fr>,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        clang-built-linux@googlegroups.com,
        Kees Cook <keescook@chromium.org>,
        Fangrui Song <maskray@google.com>
Subject: Re: [PATCH 0/2] link vdso with linker
Message-ID: <20200902052123.GA2687902@ubuntu-n2-xlarge-x86>
References: <20200901222523.1941988-1-ndesaulniers@google.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200901222523.1941988-1-ndesaulniers@google.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Sep 01, 2020 at 03:25:21PM -0700, Nick Desaulniers wrote:
> Kees Cook is working on series that adds --orphan-section=warn to arm,
> arm64, and x86.  I noticed that ppc vdso were still using cc-ldoption
> for these which I removed.  It seems this results in that flag being
> silently dropped.
> 
> I'm very confident with the first patch, but the second needs closer
> review around the error mentioned below the fold related to the .got
> section.
> 
> Nick Desaulniers (2):
>   powerpc/vdso64: link vdso64 with linker
>   powerpc/vdso32: link vdso64 with linker
> 
>  arch/powerpc/include/asm/vdso.h         | 17 ++---------------
>  arch/powerpc/kernel/vdso32/Makefile     |  7 +++++--
>  arch/powerpc/kernel/vdso32/vdso32.lds.S |  3 ++-
>  arch/powerpc/kernel/vdso64/Makefile     |  8 ++++++--
>  arch/powerpc/kernel/vdso64/vdso64.lds.S |  1 -
>  5 files changed, 15 insertions(+), 21 deletions(-)
> 
> -- 
> 2.28.0.402.g5ffc5be6b7-goog
> 

ppc44x_defconfig and powernv_defconfig start failing with this series
when LD=ld.lld is used.


$ make -skj"$(nproc)" ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu- LLVM=1 O=out/ppc32 distclean ppc44x_defconfig uImage
ld.lld: error: relocation R_PPC_REL16_LO cannot be used against symbol __kernel_datapage_offset; recompile with -fPIC
>>> defined in arch/powerpc/kernel/vdso32/datapage.o
>>> referenced by arch/powerpc/kernel/vdso32/gettimeofday.o:(__kernel_gettimeofday)

ld.lld: error: relocation R_PPC_REL16_LO cannot be used against symbol __kernel_datapage_offset; recompile with -fPIC
>>> defined in arch/powerpc/kernel/vdso32/datapage.o
>>> referenced by arch/powerpc/kernel/vdso32/gettimeofday.o:(__kernel_clock_gettime)

ld.lld: error: relocation R_PPC_REL16_LO cannot be used against symbol __kernel_datapage_offset; recompile with -fPIC
>>> defined in arch/powerpc/kernel/vdso32/datapage.o
>>> referenced by arch/powerpc/kernel/vdso32/gettimeofday.o:(__kernel_clock_getres)

ld.lld: error: relocation R_PPC_REL16_LO cannot be used against symbol __kernel_datapage_offset; recompile with -fPIC
>>> defined in arch/powerpc/kernel/vdso32/datapage.o
>>> referenced by arch/powerpc/kernel/vdso32/gettimeofday.o:(__kernel_time)
...


$ make -skj"$(nproc)" ARCH=powerpc CROSS_COMPILE=powerpc64le-linux-gnu- LLVM=1 O=out/ppc64le distclean powernv_defconfig zImage.epapr
ld.lld: error: relocation R_PPC64_REL16_LO cannot be used against symbol __kernel_datapage_offset; recompile with -fPIC
>>> defined in arch/powerpc/kernel/vdso64/datapage.o
>>> referenced by arch/powerpc/kernel/vdso64/gettimeofday.o:(__kernel_gettimeofday)

ld.lld: error: relocation R_PPC64_REL16_LO cannot be used against symbol __kernel_datapage_offset; recompile with -fPIC
>>> defined in arch/powerpc/kernel/vdso64/datapage.o
>>> referenced by arch/powerpc/kernel/vdso64/gettimeofday.o:(__kernel_clock_gettime)

ld.lld: error: relocation R_PPC64_REL16_LO cannot be used against symbol __kernel_datapage_offset; recompile with -fPIC
>>> defined in arch/powerpc/kernel/vdso64/datapage.o
>>> referenced by arch/powerpc/kernel/vdso64/gettimeofday.o:(__kernel_clock_getres)

ld.lld: error: relocation R_PPC64_REL16_LO cannot be used against symbol __kernel_datapage_offset; recompile with -fPIC
>>> defined in arch/powerpc/kernel/vdso64/datapage.o
>>> referenced by arch/powerpc/kernel/vdso64/gettimeofday.o:(__kernel_time)

ld.lld: error: relocation R_PPC64_REL16_LO cannot be used against symbol __kernel_datapage_offset; recompile with -fPIC
>>> defined in arch/powerpc/kernel/vdso64/datapage.o
>>> referenced by arch/powerpc/kernel/vdso64/cacheflush.o:(__kernel_sync_dicache)
...


We need Fangrui's patch to fix ppc44x_defconfig:

https://lore.kernel.org/lkml/20200205005054.k72fuikf6rwrgfe4@google.com/

That exact same fix is needed in arch/powerpc/kernel/vdso64/datapage.S
to fix powernv_defconfig.

Cheers,
Nathan