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    Subject[PATCH 4.4 19/70] efi/libstub/arm64: Set -fpie when building the EFI stub
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Ard Biesheuvel <ard.biesheuvel@linaro.org>

    commit 91ee5b21ee026c49e4e7483de69b55b8b47042be upstream.

    Clang may emit absolute symbol references when building in non-PIC mode,
    even when using the default 'small' code model, which is already mostly
    position independent to begin with, due to its use of adrp/add pairs
    that have a relative range of +/- 4 GB. The remedy is to pass the -fpie
    flag, which can be done safely now that the code has been updated to avoid
    GOT indirections (which may be emitted due to the compiler assuming that
    the PIC/PIE code may end up in a shared library that is subject to ELF
    symbol preemption)

    Passing -fpie when building code that needs to execute at an a priori
    unknown offset is arguably an improvement in any case, and given that
    the recent visibility changes allow the PIC build to pass with GCC as
    well, let's add -fpie for all arm64 builds rather than only for Clang.

    Tested-by: Matthias Kaehlcke <mka@chromium.org>
    Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Matt Fleming <matt@codeblueprint.co.uk>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: linux-efi@vger.kernel.org
    Link: http://lkml.kernel.org/r/20170818194947.19347-5-ard.biesheuvel@linaro.org
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/firmware/efi/libstub/Makefile | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/drivers/firmware/efi/libstub/Makefile
    +++ b/drivers/firmware/efi/libstub/Makefile
    @@ -10,7 +10,7 @@ cflags-$(CONFIG_X86) += -m$(BITS) -D__K
    -fPIC -fno-strict-aliasing -mno-red-zone \
    -mno-mmx -mno-sse -DDISABLE_BRANCH_PROFILING

    -cflags-$(CONFIG_ARM64) := $(subst -pg,,$(KBUILD_CFLAGS))
    +cflags-$(CONFIG_ARM64) := $(subst -pg,,$(KBUILD_CFLAGS)) -fpie
    cflags-$(CONFIG_ARM) := $(subst -pg,,$(KBUILD_CFLAGS)) \
    -fno-builtin -fpic -mno-single-pic-base


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