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    SubjectRe: [PATCH 4.14 114/165] x86/vdso: Fix vDSO build if a retpoline is emitted
    Hi Greg and others,

    sorry for reporting this so late, but still...

    this breaks build on older compilers, since it requires
    -mindirect-branch=thunk-inline -mindirect-branch-register even though
    retpoline support is disabled in kernel config.. is this expected?

    BR

    nik


    On Mon, Sep 03, 2018 at 06:56:40PM +0200, Greg Kroah-Hartman wrote:
    > 4.14-stable review patch. If anyone has any objections, please let me know.
    >
    > ------------------
    >
    > From: Andy Lutomirski <luto@kernel.org>
    >
    > commit 2e549b2ee0e358bc758480e716b881f9cabedb6a upstream.
    >
    > Currently, if the vDSO ends up containing an indirect branch or
    > call, GCC will emit the "external thunk" style of retpoline, and it
    > will fail to link.
    >
    > Fix it by building the vDSO with inline retpoline thunks.
    >
    > I haven't seen any reports of this triggering on an unpatched
    > kernel.
    >
    > Fixes: commit 76b043848fd2 ("x86/retpoline: Add initial retpoline support")
    > Signed-off-by: Andy Lutomirski <luto@kernel.org>
    > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    > Acked-by: Matt Rickard <matt@softrans.com.au>
    > Cc: Borislav Petkov <bp@alien8.de>
    > Cc: Jason Vas Dias <jason.vas.dias@gmail.com>
    > Cc: David Woodhouse <dwmw2@infradead.org>
    > Cc: Peter Zijlstra <peterz@infradead.org>
    > Cc: Andi Kleen <ak@linux.intel.com>
    > Cc: stable@vger.kernel.org
    > Link: https://lkml.kernel.org/r/c76538cd3afbe19c6246c2d1715bc6a60bd63985.1534448381.git.luto@kernel.org
    > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    >
    > ---
    > Makefile | 4 ++++
    > arch/x86/entry/vdso/Makefile | 6 ++++--
    > 2 files changed, 8 insertions(+), 2 deletions(-)
    >
    > --- a/Makefile
    > +++ b/Makefile
    > @@ -490,9 +490,13 @@ KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG
    > endif
    >
    > RETPOLINE_CFLAGS_GCC := -mindirect-branch=thunk-extern -mindirect-branch-register
    > +RETPOLINE_VDSO_CFLAGS_GCC := -mindirect-branch=thunk-inline -mindirect-branch-register
    > RETPOLINE_CFLAGS_CLANG := -mretpoline-external-thunk
    > +RETPOLINE_VDSO_CFLAGS_CLANG := -mretpoline
    > RETPOLINE_CFLAGS := $(call cc-option,$(RETPOLINE_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_CFLAGS_CLANG)))
    > +RETPOLINE_VDSO_CFLAGS := $(call cc-option,$(RETPOLINE_VDSO_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_VDSO_CFLAGS_CLANG)))
    > export RETPOLINE_CFLAGS
    > +export RETPOLINE_VDSO_CFLAGS
    >
    > ifeq ($(config-targets),1)
    > # ===========================================================================
    > --- a/arch/x86/entry/vdso/Makefile
    > +++ b/arch/x86/entry/vdso/Makefile
    > @@ -74,9 +74,9 @@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.d
    > CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
    > $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
    > -fno-omit-frame-pointer -foptimize-sibling-calls \
    > - -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO
    > + -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO $(RETPOLINE_VDSO_CFLAGS)
    >
    > -$(vobjs): KBUILD_CFLAGS := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS)) $(CFL)
    > +$(vobjs): KBUILD_CFLAGS := $(filter-out $(GCC_PLUGINS_CFLAGS) $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS)) $(CFL)
    >
    > #
    > # vDSO code runs in userspace and -pg doesn't help with profiling anyway.
    > @@ -147,11 +147,13 @@ KBUILD_CFLAGS_32 := $(filter-out -mcmode
    > KBUILD_CFLAGS_32 := $(filter-out -fno-pic,$(KBUILD_CFLAGS_32))
    > KBUILD_CFLAGS_32 := $(filter-out -mfentry,$(KBUILD_CFLAGS_32))
    > KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32))
    > +KBUILD_CFLAGS_32 := $(filter-out $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS_32))
    > KBUILD_CFLAGS_32 += -m32 -msoft-float -mregparm=0 -fpic
    > KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector)
    > KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls)
    > KBUILD_CFLAGS_32 += -fno-omit-frame-pointer
    > KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING
    > +KBUILD_CFLAGS_32 += $(RETPOLINE_VDSO_CFLAGS)
    > $(obj)/vdso32.so.dbg: KBUILD_CFLAGS = $(KBUILD_CFLAGS_32)
    >
    > $(obj)/vdso32.so.dbg: FORCE \
    >
    >

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