RESEND [PATCH 6/6] arm64: Wire up and expose the new compat vDSO

Mark Salyzyn
2018-06-18T15:10:31Z

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: James Morse <james.morse@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dmitry Safonov <dsafonov@virtuozzo.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Andy Gross <andy.gross@linaro.org>
Cc: Andrew Pinski <apinski@cavium.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: Jeremy Linton <Jeremy.Linton@arm.com>
---
arch/arm64/Kconfig | 24 ++++++++++++++++++++++++
arch/arm64/Makefile | 36 ++++++++++++++++++++++++++++++++++--
arch/arm64/kernel/Makefile | 3 +++
3 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 11b4c6aef7d7..eb9d3fc45f6b 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1330,6 +1330,30 @@ 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 45272266dafb..f548123e1609 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -49,9 +49,39 @@ $(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_AFLAGS += $(lseinstr) $(brokengasinst)
+KBUILD_CFLAGS += $(call cc-option, -mpc-relative-literal-loads)
+KBUILD_AFLAGS += $(lseinstr) $(brokengasinst) $(vdso32)

KBUILD_CFLAGS += $(call cc-option,-mabi=lp64)
KBUILD_AFLAGS += $(call cc-option,-mabi=lp64)
@@ -155,6 +185,8 @@ 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 c16be3cf39bf..628d0308d809 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -28,7 +28,9 @@ $(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
@@ -59,6 +61,7 @@ arm64-obj-$(CONFIG_ARM_SDE_INTERFACE) += sdei.o
arm64-obj-$(CONFIG_ARM64_SSBD) += ssbd.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
--
2.18.0.rc1.244.gcf134e6275-goog