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    Subject[PATCH 6/6] arm64: Wire up and expose the new compat vDSO
    Date
    From: Kevin Brodsky <kevin.brodsky@arm.com>

    Expose the new compat vDSO via the COMPAT_VDSO config option.

    The option is not enabled in defconfig because we really need a 32-bit
    compiler this time, and we rely on the user to provide it themselves
    by setting CROSS_COMPILE_ARM32. Therefore enabling the option by
    default would make little sense, since the user must explicitly set a
    non-standard environment variable anyway.

    CONFIG_COMPAT_VDSO is not directly used in the code, because we want
    to ignore it (build as if it were not set) if the user didn't set
    CROSS_COMPILE_ARM32. If the variable has been set to a valid prefix,
    CONFIG_VDSO32 will be set; this is the option that the code and
    Makefiles test.

    For more flexibility, like CROSS_COMPILE, CROSS_COMPILE_ARM32 can also
    be set via CONFIG_CROSS_COMPILE_ARM32 (the environment variable
    overrides the config option, as expected).

    Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
    Signed-off-by: Mark Salyzyn <salyzyn@android.com>
    Cc: Catalin Marinas <catalin.marinas@arm.com>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: Dave Martin <Dave.Martin@arm.com>
    Cc: "Eric W. Biederman" <ebiederm@xmission.com>
    Cc: linux-arm-kernel@lists.infradead.org
    Cc: linux-kernel@vger.kernel.org
    ---
    arch/arm64/Kconfig | 24 ++++++++++++++++++++++++
    arch/arm64/Makefile | 35 +++++++++++++++++++++++++++++++++--
    arch/arm64/kernel/Makefile | 3 +++
    3 files changed, 60 insertions(+), 2 deletions(-)

    diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
    index d8a4fda50477..379d0154b363 100644
    --- a/arch/arm64/Kconfig
    +++ b/arch/arm64/Kconfig
    @@ -1183,6 +1183,30 @@ config SYSVIPC_COMPAT
    def_bool y
    depends on COMPAT && SYSVIPC

    +config COMPAT_VDSO
    + bool "32-bit vDSO"
    + depends on COMPAT
    + default n
    + help
    + Warning: a 32-bit toolchain is necessary to build the vDSO. You
    + must explicitly define which toolchain should be used by setting
    + CROSS_COMPILE_ARM32 to the prefix of the 32-bit toolchain (same format
    + as CROSS_COMPILE). If CROSS_COMPILE_ARM32 is empty, a warning will be
    + printed and the kernel will be built as if COMPAT_VDSO had not been
    + set. If CROSS_COMPILE_ARM32 is set to an invalid prefix, compilation
    + will be aborted.
    +
    + Provide a vDSO to 32-bit processes. It includes the symbols provided
    + by the vDSO from the 32-bit kernel, so that a 32-bit libc can use
    + the compat vDSO without modification. It also provides sigreturn
    + trampolines, replacing the sigreturn page.
    +
    +config CROSS_COMPILE_ARM32
    + string "32-bit toolchain prefix"
    + help
    + Same as setting CROSS_COMPILE_ARM32 in the environment, but saved for
    + future builds. The environment variable overrides this config option.
    +
    endmenu

    menu "Power management options"
    diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
    index 939b310913cf..baf36f0a992d 100644
    --- a/arch/arm64/Makefile
    +++ b/arch/arm64/Makefile
    @@ -45,10 +45,39 @@ $(warning Detected assembler with broken .inst; disassembly will be unreliable)
    endif
    endif

    -KBUILD_CFLAGS += -mgeneral-regs-only $(lseinstr) $(brokengasinst)
    +ifeq ($(CONFIG_COMPAT_VDSO), y)
    + CROSS_COMPILE_ARM32 ?= $(CONFIG_CROSS_COMPILE_ARM32:"%"=%)
    +
    + # Check that the user has provided a valid prefix for the 32-bit toolchain.
    + # To prevent selecting the system $(cc-name) by default, the prefix is not
    + # allowed to be empty, unlike CROSS_COMPILE. In the unlikely event that the
    + # system $(cc-name) is actually the 32-bit ARM compiler to be used, the
    + # variable can be set to the dirname (e.g. CROSS_COMPILE_ARM32=/usr/bin/).
    + # Note: this Makefile is read both before and after regenerating the config
    + # (if needed). Any warning appearing before the config has been regenerated
    + # should be ignored. If the error is triggered and you set
    + # CONFIG_CROSS_COMPILE_ARM32, set CROSS_COMPILE_ARM32 to an appropriate value
    + # when invoking make and fix CONFIG_CROSS_COMPILE_ARM32.
    + ifeq ($(CROSS_COMPILE_ARM32),)
    + $(error CROSS_COMPILE_ARM32 not defined or empty, the compat vDSO will not be built)
    + else ifeq ($(cc-name),clang)
    + export CLANG_TRIPLE_ARM32 ?= $(CROSS_COMPILE_ARM32)
    + export CLANG_TARGET_ARM32 := --target=$(notdir $(CLANG_TRIPLE_ARM32:%-=%))
    + export CONFIG_VDSO32 := y
    + vdso32 := -DCONFIG_VDSO32=1
    + else ifeq ($(shell which $(CROSS_COMPILE_ARM32)$(cc-name) 2> /dev/null),)
    + $(error $(CROSS_COMPILE_ARM32)$(cc-name) not found, check CROSS_COMPILE_ARM32)
    + else
    + export CROSS_COMPILE_ARM32
    + export CONFIG_VDSO32 := y
    + vdso32 := -DCONFIG_VDSO32=1
    + endif
    +endif
    +
    +KBUILD_CFLAGS += -mgeneral-regs-only $(lseinstr) $(brokengasinst) $(vdso32)
    KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
    KBUILD_CFLAGS += $(call cc-option, -mpc-relative-literal-loads)
    -KBUILD_AFLAGS += $(lseinstr) $(brokengasinst)
    +KBUILD_AFLAGS += $(lseinstr) $(brokengasinst) $(vdso32)

    KBUILD_CFLAGS += $(call cc-option,-mabi=lp64)
    KBUILD_AFLAGS += $(call cc-option,-mabi=lp64)
    @@ -157,6 +186,8 @@ archclean:
    prepare: vdso_prepare
    vdso_prepare: prepare0
    $(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso include/generated/vdso-offsets.h
    + $(if $(CONFIG_VDSO32),$(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso32 \
    + include/generated/vdso32-offsets.h)

    define archhelp
    echo '* Image.gz - Compressed kernel image (arch/$(ARCH)/boot/Image.gz)'
    diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
    index 6e969f3cde6c..5db2b239cd68 100644
    --- a/arch/arm64/kernel/Makefile
    +++ b/arch/arm64/kernel/Makefile
    @@ -30,7 +30,9 @@ $(obj)/%.stub.o: $(obj)/%.o FORCE

    arm64-obj-$(CONFIG_COMPAT) += sys32.o signal32.o \
    sys_compat.o entry32.o
    +ifneq ($(CONFIG_VDSO32),y)
    arm64-obj-$(CONFIG_COMPAT) += sigreturn32.o
    +endif
    arm64-obj-$(CONFIG_KUSER_HELPERS) += kuser32.o
    arm64-obj-$(CONFIG_FUNCTION_TRACER) += ftrace.o entry-ftrace.o
    arm64-obj-$(CONFIG_MODULES) += arm64ksyms.o module.o
    @@ -58,6 +60,7 @@ arm64-reloc-test-y := reloc_test_core.o reloc_test_syms.o
    arm64-obj-$(CONFIG_CRASH_DUMP) += crash_dump.o

    obj-y += $(arm64-obj-y) vdso/ probes/
    +obj-$(CONFIG_VDSO32) += vdso32/
    obj-m += $(arm64-obj-m)
    head-y := head.o
    extra-y += $(head-y) vmlinux.lds
    --
    2.15.0.448.gf294e3d99a-goog
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