linux-kernel - [PATCH] ARM: vdso: use $(LD) instead of $(CC) to link VDSO

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Message-Id: <20190411092933.6413-1-yamada.masahiro@socionext.com>
Date:   Thu, 11 Apr 2019 18:29:33 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     Olof Johansson <olof@...om.net>, Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>
Subject: [PATCH] ARM: vdso: use $(LD) instead of $(CC) to link VDSO

We use $(LD) to link vmlinux, modules, decompressors, etc.

VDSO is the only exceptional case where $(CC) is used as the linker
driver, but I do not know why we need to do so. VDSO uses a special
linker script, and does not link standard libraries at all.

I changed the Makefile to use $(LD) rather than $(CC). I confirmed
the same vdso.so.raw was still produced.

Users will be able to use their favorite linker (e.g. lld instead of
of bfd) by passing LD= from the command line.

My plan is to rewrite all VDSO Makefiles to use $(LD), then delete
cc-ldoption.

Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
---

 arch/arm/vdso/Makefile | 21 ++++++++-------------
 1 file changed, 8 insertions(+), 13 deletions(-)

diff --git a/arch/arm/vdso/Makefile b/arch/arm/vdso/Makefile
index f4efff9d3afb..fadf554d9391 100644
--- a/arch/arm/vdso/Makefile
+++ b/arch/arm/vdso/Makefile
@@ -10,12 +10,12 @@ obj-vdso := $(addprefix $(obj)/, $(obj-vdso))
 ccflags-y := -fPIC -fno-common -fno-builtin -fno-stack-protector
 ccflags-y += -DDISABLE_BRANCH_PROFILING
 
-VDSO_LDFLAGS := -Wl,-Bsymbolic -Wl,--no-undefined -Wl,-soname=linux-vdso.so.1
-VDSO_LDFLAGS += -Wl,-z,max-page-size=4096 -Wl,-z,common-page-size=4096
-VDSO_LDFLAGS += -nostdlib -shared
-VDSO_LDFLAGS += $(call cc-ldoption, -Wl$(comma)--hash-style=sysv)
-VDSO_LDFLAGS += $(call cc-ldoption, -Wl$(comma)--build-id)
-VDSO_LDFLAGS += $(call cc-ldoption, -fuse-ld=bfd)
+ldflags-y = -Bsymbolic --no-undefined -soname=linux-vdso.so.1 \
+	    -z max-page-size=4096 -z common-page-size=4096 \
+	    -nostdlib -shared \
+	    $(call ld-option, --hash-style=sysv) \
+	    $(call ld-option, --build-id) \
+	    -T
 
 obj-$(CONFIG_VDSO) += vdso.o
 extra-$(CONFIG_VDSO) += vdso.lds
@@ -37,8 +37,8 @@ KCOV_INSTRUMENT := n
 $(obj)/vdso.o : $(obj)/vdso.so
 
 # Link rule for the .so file
-$(obj)/vdso.so.raw: $(src)/vdso.lds $(obj-vdso) FORCE
-	$(call if_changed,vdsold)
+$(obj)/vdso.so.raw: $(obj)/vdso.lds $(obj-vdso) FORCE
+	$(call if_changed,ld)
 
 $(obj)/vdso.so.dbg: $(obj)/vdso.so.raw $(obj)/vdsomunge FORCE
 	$(call if_changed,vdsomunge)
@@ -48,11 +48,6 @@ $(obj)/%.so: OBJCOPYFLAGS := -S
 $(obj)/%.so: $(obj)/%.so.dbg FORCE
 	$(call if_changed,objcopy)
 
-# Actual build commands
-quiet_cmd_vdsold = VDSO    $@
-      cmd_vdsold = $(CC) $(c_flags) $(VDSO_LDFLAGS) \
-                   -Wl,-T $(filter %.lds,$^) $(filter %.o,$^) -o $@
-
 quiet_cmd_vdsomunge = MUNGE   $@
       cmd_vdsomunge = $(objtree)/$(obj)/vdsomunge $< $@
 
-- 
2.17.1