arm64: vdso: Enable vDSO compat support

Add vDSO compat support to the arm64 build system.

Signed-off-by: Vincenzo Frascino <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Tested-by: Shijith Thotton <[e-mail]>
Tested-by: Andre Przywara <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: Catalin Marinas <[e-mail]>
Cc: Will Deacon <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Russell King <[e-mail]>
Cc: Ralf Baechle <[e-mail]>
Cc: Paul Burton <[e-mail]>
Cc: Daniel Lezcano <[e-mail]>
Cc: Mark Salyzyn <[e-mail]>
Cc: Peter Collingbourne <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Cc: Dmitry Safonov <[e-mail]>
Cc: Rasmus Villemoes <[e-mail]>
Cc: Huw Davies <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

arch/arm64/Kconfig

···
 	select GENERIC_STRNLEN_USER
 	select GENERIC_TIME_VSYSCALL
 	select GENERIC_GETTIMEOFDAY
+	select GENERIC_COMPAT_VDSO if (!CPU_BIG_ENDIAN && COMPAT)
 	select HANDLE_DOMAIN_IRQ
 	select HARDIRQS_SW_RESEND
 	select HAVE_PCI

arch/arm64/Makefile

···
   endif
 endif
 
-KBUILD_CFLAGS	+= -mgeneral-regs-only $(lseinstr) $(brokengasinst)
+ifeq ($(CONFIG_GENERIC_COMPAT_VDSO), y)
+  CROSS_COMPILE_COMPAT ?= $(CONFIG_CROSS_COMPILE_COMPAT_VDSO:"%"=%)
+
+  ifeq ($(CONFIG_CC_IS_CLANG), y)
+    $(warning CROSS_COMPILE_COMPAT is clang, the compat vDSO will not be built)
+  else ifeq ($(CROSS_COMPILE_COMPAT),)
+    $(warning CROSS_COMPILE_COMPAT not defined or empty, the compat vDSO will not be built)
+  else ifeq ($(shell which $(CROSS_COMPILE_COMPAT)gcc 2> /dev/null),)
+    $(error $(CROSS_COMPILE_COMPAT)gcc not found, check CROSS_COMPILE_COMPAT)
+  else
+    export CROSS_COMPILE_COMPAT
+    export CONFIG_COMPAT_VDSO := y
+    compat_vdso := -DCONFIG_COMPAT_VDSO=1
+  endif
+endif
+
+KBUILD_CFLAGS	+= -mgeneral-regs-only $(lseinstr) $(brokengasinst) $(compat_vdso)
 KBUILD_CFLAGS	+= -fno-asynchronous-unwind-tables
 KBUILD_CFLAGS	+= $(call cc-disable-warning, psabi)
-KBUILD_AFLAGS	+= $(lseinstr) $(brokengasinst)
+KBUILD_AFLAGS	+= $(lseinstr) $(brokengasinst) $(compat_vdso)
 
 KBUILD_CFLAGS	+= $(call cc-option,-mabi=lp64)
 KBUILD_AFLAGS	+= $(call cc-option,-mabi=lp64)
···
 prepare: vdso_prepare
 vdso_prepare: prepare0
 	$(Q)$(MAKE) $(build)=arch/arm64/kernel/vdso include/generated/vdso-offsets.h
+	$(if $(CONFIG_COMPAT_VDSO),$(Q)$(MAKE) \
+		$(build)=arch/arm64/kernel/vdso32  \
+		include/generated/vdso32-offsets.h)
 endif
 
 define archhelp

arch/arm64/kernel/Makefile

···
 	$(call if_changed,objcopy)
 
 obj-$(CONFIG_COMPAT)			+= sys32.o signal32.o			\
-					   sigreturn32.o sys_compat.o
+					   sys_compat.o
+ifneq ($(CONFIG_COMPAT_VDSO), y)
+obj-$(CONFIG_COMPAT)			+= sigreturn32.o
+endif
 obj-$(CONFIG_KUSER_HELPERS)		+= kuser32.o
 obj-$(CONFIG_FUNCTION_TRACER)		+= ftrace.o entry-ftrace.o
 obj-$(CONFIG_MODULES)			+= module.o
···
 obj-$(CONFIG_ARM64_PTR_AUTH)		+= pointer_auth.o
 
 obj-y					+= vdso/ probes/
+obj-$(CONFIG_COMPAT_VDSO)		+= vdso32/
 head-y					:= head.o
 extra-y					+= $(head-y) vmlinux.lds