[PATCH v3 2/4] MIPS: VDSO: Move disabling the VDSO logic to Kconfig

Nathan Chancellor
2020-04-23T17:18:34Z

After commit 9553d16fa671 ("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>
---

v2 -> v3:

* Fix CONFIG macro in arch/mips/vdso/vdso.lds.S, thanks to Sedat for
catching it.

v1 -> v2:

* New patch.

arch/mips/Kconfig | 2 ++
arch/mips/vdso/Kconfig | 18 ++++++++++++++++++
arch/mips/vdso/Makefile | 30 ++----------------------------
arch/mips/vdso/vdso.lds.S | 2 +-
4 files changed, 23 insertions(+), 29 deletions(-)
create mode 100644 arch/mips/vdso/Kconfig

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 690718b3701af..45220e4b8a653 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -3275,3 +3275,5 @@ endmenu
source "drivers/firmware/Kconfig"

source "arch/mips/kvm/Kconfig"
+
+source "arch/mips/vdso/Kconfig"
diff --git a/arch/mips/vdso/Kconfig b/arch/mips/vdso/Kconfig
new file mode 100644
index 0000000000000..36a52158d849b
--- /dev/null
+++ b/arch/mips/vdso/Kconfig
@@ -0,0 +1,18 @@
+# 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)
diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
index d7fe8408603e8..92b53d1df42c3 100644
--- a/arch/mips/vdso/Makefile
+++ b/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.
diff --git a/arch/mips/vdso/vdso.lds.S b/arch/mips/vdso/vdso.lds.S
index da4627430aba4..d90b65724d78e 100644
--- a/arch/mips/vdso/vdso.lds.S
+++ b/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;
--
2.26.2