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    Subject[PATCH 06/11] stackprotector: update make rules
    Date
    Impact: no default -fno-stack-protector if stackp is enabled, cleanup

    Stackprotector make rules had the following problems.

    * cc support test and warning are scattered across makefile and
    kernel/panic.c.

    * -fno-stack-protector was always added regardless of configuration.

    Update such that cc support test and warning are contained in makefile
    and -fno-stack-protector is added iff stackp is turned off. While at
    it, prepare for 32bit support.

    Signed-off-by: Tejun Heo <tj@kernel.org>
    ---
    Makefile | 3 ++-
    arch/x86/Makefile | 17 ++++++++++-------
    kernel/panic.c | 4 ----
    scripts/gcc-x86_64-has-stack-protector.sh | 4 +++-
    4 files changed, 15 insertions(+), 13 deletions(-)

    diff --git a/Makefile b/Makefile
    index d0634bc..1ab7cef 100644
    --- a/Makefile
    +++ b/Makefile
    @@ -532,8 +532,9 @@ KBUILD_CFLAGS += $(call cc-option,-Wframe-larger-than=${CONFIG_FRAME_WARN})
    endif

    # Force gcc to behave correct even for buggy distributions
    -# Arch Makefiles may override this setting
    +ifndef CONFIG_CC_STACKPROTECTOR
    KBUILD_CFLAGS += $(call cc-option, -fno-stack-protector)
    +endif

    ifdef CONFIG_FRAME_POINTER
    KBUILD_CFLAGS += -fno-omit-frame-pointer -fno-optimize-sibling-calls
    diff --git a/arch/x86/Makefile b/arch/x86/Makefile
    index eb7b986..8597305 100644
    --- a/arch/x86/Makefile
    +++ b/arch/x86/Makefile
    @@ -70,14 +70,17 @@ else
    # this works around some issues with generating unwind tables in older gccs
    # newer gccs do it by default
    KBUILD_CFLAGS += -maccumulate-outgoing-args
    +endif

    - stackp := $(CONFIG_SHELL) $(srctree)/scripts/gcc-x86_64-has-stack-protector.sh
    - stackp-$(CONFIG_CC_STACKPROTECTOR) := $(shell $(stackp) \
    - "$(CC)" "-fstack-protector -DGCC_HAS_SP" )
    - stackp-$(CONFIG_CC_STACKPROTECTOR_ALL) += $(shell $(stackp) \
    - "$(CC)" -fstack-protector-all )
    -
    - KBUILD_CFLAGS += $(stackp-y)
    +ifdef CONFIG_CC_STACKPROTECTOR
    + cc_has_sp := $(srctree)/scripts/gcc-x86_$(BITS)-has-stack-protector.sh
    + ifeq ($(shell $(CONFIG_SHELL) $(cc_has_sp) $(CC)),y)
    + stackp-y := -fstack-protector
    + stackp-$(CONFIG_CC_STACKPROTECTOR_ALL) += -fstack-protector-all
    + KBUILD_CFLAGS += $(stackp-y)
    + else
    + $(warning stack protector enabled but no compiler support)
    + endif
    endif

    # Don't unroll struct assignments with kmemcheck enabled
    diff --git a/kernel/panic.c b/kernel/panic.c
    index 33cab3d..32fe4ef 100644
    --- a/kernel/panic.c
    +++ b/kernel/panic.c
    @@ -359,10 +359,6 @@ EXPORT_SYMBOL(warn_slowpath);

    #ifdef CONFIG_CC_STACKPROTECTOR

    -#ifndef GCC_HAS_SP
    -#warning You have selected the CONFIG_CC_STACKPROTECTOR option, but the gcc used does not support this.
    -#endif
    -
    /*
    * Called when gcc's -fstack-protector feature is used, and
    * gcc detects corruption of the on-stack canary value
    diff --git a/scripts/gcc-x86_64-has-stack-protector.sh b/scripts/gcc-x86_64-has-stack-protector.sh
    index 325c0a1..2d69fcd 100644
    --- a/scripts/gcc-x86_64-has-stack-protector.sh
    +++ b/scripts/gcc-x86_64-has-stack-protector.sh
    @@ -2,5 +2,7 @@

    echo "int foo(void) { char X[200]; return 3; }" | $1 -S -xc -c -O0 -mcmodel=kernel -fstack-protector - -o - 2> /dev/null | grep -q "%gs"
    if [ "$?" -eq "0" ] ; then
    - echo $2
    + echo y
    +else
    + echo n
    fi
    --
    1.6.0.2


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