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Date:   Wed, 6 May 2020 10:17:06 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>
Cc:     linux-mips@...r.kernel.org,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        "Maciej W . Rozycki" <macro@...ux-mips.org>,
        Fangrui Song <maskray@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Burton <paulburton@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Jouni Hogander <jouni.hogander@...kie.com>,
        Kevin Darbyshire-Bryant <ldir@...byshire-bryant.me.uk>,
        Borislav Petkov <bp@...e.de>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re:

On Tue, May 5, 2020 at 10:52 PM Jiaxun Yang <jiaxun.yang@...goat.com> wrote:
>
> Subject: [PATCH v6] MIPS: Truncate link address into 32bit for 32bit kernel
> In-Reply-To: <20200413062651.3992652-1-jiaxun.yang@...goat.com>
>
> LLD failed to link vmlinux with 64bit load address for 32bit ELF
> while bfd will strip 64bit address into 32bit silently.
> To fix LLD build, we should truncate load address provided by platform
> into 32bit for 32bit kernel.
>
> Signed-off-by: Jiaxun Yang <jiaxun.yang@...goat.com>
> Link: https://github.com/ClangBuiltLinux/linux/issues/786
> Link: https://sourceware.org/bugzilla/show_bug.cgi?id=25784
> Reviewed-by: Fangrui Song <maskray@...gle.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> Tested-by: Nathan Chancellor <natechancellor@...il.com>
> Cc: Maciej W. Rozycki <macro@...ux-mips.org>

Cool, this revision looks a bit simpler. Thanks for chasing this.
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
> V2: Take MaskRay's shell magic.
>
> V3: After spent an hour on dealing with special character issue in
> Makefile, I gave up to do shell hacks and write a util in C instead.
> Thanks Maciej for pointing out Makefile variable problem.
>
> v4: Finally we managed to find a Makefile method to do it properly
> thanks to Kees. As it's too far from the initial version, I removed
> Review & Test tag from Nick and Fangrui and Cc instead.
>
> v5: Care vmlinuz as well.
>
> v6: Rename to LIKER_LOAD_ADDRESS
> ---
>  arch/mips/Makefile                 | 13 ++++++++++++-
>  arch/mips/boot/compressed/Makefile |  2 +-
>  arch/mips/kernel/vmlinux.lds.S     |  2 +-
>  3 files changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/arch/mips/Makefile b/arch/mips/Makefile
> index e1c44aed8156..68c0f22fefc0 100644
> --- a/arch/mips/Makefile
> +++ b/arch/mips/Makefile
> @@ -288,12 +288,23 @@ ifdef CONFIG_64BIT
>    endif
>  endif
>
> +# When linking a 32-bit executable the LLVM linker cannot cope with a
> +# 32-bit load address that has been sign-extended to 64 bits.  Simply
> +# remove the upper 32 bits then, as it is safe to do so with other
> +# linkers.
> +ifdef CONFIG_64BIT
> +       load-ld                 = $(load-y)
> +else
> +       load-ld                 = $(subst 0xffffffff,0x,$(load-y))
> +endif
> +
>  KBUILD_AFLAGS  += $(cflags-y)
>  KBUILD_CFLAGS  += $(cflags-y)
> -KBUILD_CPPFLAGS += -DVMLINUX_LOAD_ADDRESS=$(load-y)
> +KBUILD_CPPFLAGS += -DVMLINUX_LOAD_ADDRESS=$(load-y) -DLINKER_LOAD_ADDRESS=$(load-ld)
>  KBUILD_CPPFLAGS += -DDATAOFFSET=$(if $(dataoffset-y),$(dataoffset-y),0)
>
>  bootvars-y     = VMLINUX_LOAD_ADDRESS=$(load-y) \
> +                 LINKER_LOAD_ADDRESS=$(load-ld) \
>                   VMLINUX_ENTRY_ADDRESS=$(entry-y) \
>                   PLATFORM="$(platform-y)" \
>                   ITS_INPUTS="$(its-y)"
> diff --git a/arch/mips/boot/compressed/Makefile b/arch/mips/boot/compressed/Makefile
> index 0df0ee8a298d..3d391256ab7e 100644
> --- a/arch/mips/boot/compressed/Makefile
> +++ b/arch/mips/boot/compressed/Makefile
> @@ -90,7 +90,7 @@ ifneq ($(zload-y),)
>  VMLINUZ_LOAD_ADDRESS := $(zload-y)
>  else
>  VMLINUZ_LOAD_ADDRESS = $(shell $(obj)/calc_vmlinuz_load_addr \
> -               $(obj)/vmlinux.bin $(VMLINUX_LOAD_ADDRESS))
> +               $(obj)/vmlinux.bin $(LINKER_LOAD_ADDRESS))
>  endif
>  UIMAGE_LOADADDR = $(VMLINUZ_LOAD_ADDRESS)
>
> diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S
> index a5f00ec73ea6..5226cd8e4bee 100644
> --- a/arch/mips/kernel/vmlinux.lds.S
> +++ b/arch/mips/kernel/vmlinux.lds.S
> @@ -55,7 +55,7 @@ SECTIONS
>         /* . = 0xa800000000300000; */
>         . = 0xffffffff80300000;
>  #endif
> -       . = VMLINUX_LOAD_ADDRESS;
> +       . = LINKER_LOAD_ADDRESS;
>         /* read-only */
>         _text = .;      /* Text and read-only data */
>         .text : {
>
> --

-- 
Thanks,
~Nick Desaulniers

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