MIPS: VDSO: Move disabling the VDSO logic to Kconfig

After commit 9553d16f ("init/kconfig: Add LD_VERSION Kconfig"), we
have access to GNU ld's version at configuration time. As a result, we
can make it clearer under what configuration circumstances the MIPS VDSO
needs to be disabled.

This is a prerequisite for getting rid of the MIPS VDSO binutils
warning and linking the VDSO when LD is ld.lld. Wrapping the call to
ld-ifversion with CONFIG_LD_IS_LLD does not work because the config
values are wiped away during 'make clean'.
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/Kconfig

@@ -3214,3 +3214,5 @@ endmenu
 source "drivers/firmware/Kconfig"
 
 source "arch/mips/kvm/Kconfig"
+
+source "arch/mips/vdso/Kconfig"

arch/mips/vdso/Kconfig

+# For the pre-R6 code in arch/mips/vdso/vdso.h for locating
+# the base address of VDSO, the linker will emit a R_MIPS_PC32
+# relocation in binutils > 2.25 but it will fail with older versions
+# because that relocation is not supported for that symbol. As a result
+# of which we are forced to disable the VDSO symbols when building
+# with < 2.25 binutils on pre-R6 kernels. For more references on why we
+# can't use other methods to get the base address of VDSO please refer to
+# the comments on that file.
+#
+# GCC (at least up to version 9.2) appears to emit function calls that make use
+# of the GOT when targeting microMIPS, which we can't use in the VDSO due to
+# the lack of relocations. As such, we disable the VDSO for microMIPS builds.
+
+config MIPS_LD_CAN_LINK_VDSO
+	def_bool LD_VERSION >= 225000000
+
+config MIPS_DISABLE_VDSO
+	def_bool CPU_MICROMIPS || (!CPU_MIPSR6 && !MIPS_LD_CAN_LINK_VDSO)

arch/mips/vdso/Makefile

@@ -52,37 +52,11 @@ endif
 
 CFLAGS_REMOVE_vgettimeofday.o = -pg
 
-DISABLE_VDSO := n
-
-#
-# For the pre-R6 code in arch/mips/vdso/vdso.h for locating
-# the base address of VDSO, the linker will emit a R_MIPS_PC32
-# relocation in binutils > 2.25 but it will fail with older versions
-# because that relocation is not supported for that symbol. As a result
-# of which we are forced to disable the VDSO symbols when building
-# with < 2.25 binutils on pre-R6 kernels. For more references on why we
-# can't use other methods to get the base address of VDSO please refer to
-# the comments on that file.
-#
-ifndef CONFIG_CPU_MIPSR6
-  ifeq ($(call ld-ifversion, -lt, 225000000, y),y)
+ifdef CONFIG_MIPS_DISABLE_VDSO
+  ifndef CONFIG_MIPS_LD_CAN_LINK_VDSO
     $(warning MIPS VDSO requires binutils >= 2.25)
-    DISABLE_VDSO := y
   endif
-endif
-
-#
-# GCC (at least up to version 9.2) appears to emit function calls that make use
-# of the GOT when targeting microMIPS, which we can't use in the VDSO due to
-# the lack of relocations. As such, we disable the VDSO for microMIPS builds.
-#
-ifdef CONFIG_CPU_MICROMIPS
-  DISABLE_VDSO := y
-endif
-
-ifeq ($(DISABLE_VDSO),y)
   obj-vdso-y := $(filter-out vgettimeofday.o, $(obj-vdso-y))
-  ccflags-vdso += -DDISABLE_MIPS_VDSO
 endif
 
 # VDSO linker flags.

arch/mips/vdso/vdso.lds.S

@@ -91,7 +91,7 @@ PHDRS
 VERSION
 {
 	LINUX_2.6 {
-#ifndef DISABLE_MIPS_VDSO
+#ifndef CONFIG_MIPS_DISABLE_VDSO
 	global:
 		__vdso_clock_gettime;
 		__vdso_gettimeofday;