[PATCH v4 2/5] MIPS: VDSO: Move disabling the VDSO logic to Kconfig

From: Nathan Chancellor <natechancellor@gmail.com>
To: Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Masahiro Yamada <masahiroy@kernel.org>
Cc: linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
	clang-built-linux@googlegroups.com, linux-kbuild@vger.kernel.org,
	Nick Desaulniers <ndesaulniers@google.com>,
	Fangrui Song <maskray@google.com>,
	Sami Tolvanen <samitolvanen@google.com>,
	Dmitry Golovin <dima@golovin.in>,
	Sedat Dilek <sedat.dilek@gmail.com>,
	Nathan Chancellor <natechancellor@gmail.com>
Subject: [PATCH v4 2/5] MIPS: VDSO: Move disabling the VDSO logic to Kconfig
Date: Tue, 28 Apr 2020 15:14:16 -0700	[thread overview]
Message-ID: <20200428221419.2530697-3-natechancellor@gmail.com> (raw)
In-Reply-To: <20200428221419.2530697-1-natechancellor@gmail.com>

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>
---

v3 -> v4:

* No changes.

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

