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    Subject[PATCH 4.9 42/86] x86/retpoline: Support retpoline builds with Clang
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

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

    From: David Woodhouse <dwmw@amazon.co.uk>

    commit 87358710c1fb4f1bf96bbe2349975ff9953fc9b2 upstream.

    Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
    Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: arjan.van.de.ven@intel.com
    Cc: bp@alien8.de
    Cc: dave.hansen@intel.com
    Cc: jmattson@google.com
    Cc: karahmed@amazon.de
    Cc: kvm@vger.kernel.org
    Cc: pbonzini@redhat.com
    Cc: rkrcmar@redhat.com
    Link: http://lkml.kernel.org/r/1519037457-7643-5-git-send-email-dwmw@amazon.co.uk
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/Makefile | 5 ++++-
    include/linux/compiler-clang.h | 5 +++++
    include/linux/compiler-gcc.h | 4 ++++
    include/linux/init.h | 8 ++++----
    4 files changed, 17 insertions(+), 5 deletions(-)

    --- a/arch/x86/Makefile
    +++ b/arch/x86/Makefile
    @@ -184,7 +184,10 @@ KBUILD_AFLAGS += $(mflags-y)

    # Avoid indirect branches in kernel to deal with Spectre
    ifdef CONFIG_RETPOLINE
    - RETPOLINE_CFLAGS += $(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register)
    + RETPOLINE_CFLAGS_GCC := -mindirect-branch=thunk-extern -mindirect-branch-register
    + RETPOLINE_CFLAGS_CLANG := -mretpoline-external-thunk
    +
    + RETPOLINE_CFLAGS += $(call cc-option,$(RETPOLINE_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_CFLAGS_CLANG)))
    ifneq ($(RETPOLINE_CFLAGS),)
    KBUILD_CFLAGS += $(RETPOLINE_CFLAGS) -DRETPOLINE
    endif
    --- a/include/linux/compiler-clang.h
    +++ b/include/linux/compiler-clang.h
    @@ -15,3 +15,8 @@
    * with any version that can compile the kernel
    */
    #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
    +
    +/* Clang doesn't have a way to turn it off per-function, yet. */
    +#ifdef __noretpoline
    +#undef __noretpoline
    +#endif
    --- a/include/linux/compiler-gcc.h
    +++ b/include/linux/compiler-gcc.h
    @@ -88,6 +88,10 @@
    #define __weak __attribute__((weak))
    #define __alias(symbol) __attribute__((alias(#symbol)))

    +#ifdef RETPOLINE
    +#define __noretpoline __attribute__((indirect_branch("keep")))
    +#endif
    +
    /*
    * it doesn't make sense on ARM (currently the only user of __naked)
    * to trace naked functions because then mcount is called without
    --- a/include/linux/init.h
    +++ b/include/linux/init.h
    @@ -5,10 +5,10 @@
    #include <linux/types.h>

    /* Built-in __init functions needn't be compiled with retpoline */
    -#if defined(RETPOLINE) && !defined(MODULE)
    -#define __noretpoline __attribute__((indirect_branch("keep")))
    +#if defined(__noretpoline) && !defined(MODULE)
    +#define __noinitretpoline __noretpoline
    #else
    -#define __noretpoline
    +#define __noinitretpoline
    #endif

    /* These macros are used to mark some functions or
    @@ -46,7 +46,7 @@

    /* These are for everybody (although not all archs will actually
    discard it in modules) */
    -#define __init __section(.init.text) __cold notrace __latent_entropy __noretpoline
    +#define __init __section(.init.text) __cold notrace __latent_entropy __noinitretpoline
    #define __initdata __section(.init.data)
    #define __initconst __section(.init.rodata)
    #define __exitdata __section(.exit.data)

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