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Subject[PATCH v2 1/2] x86/vdso: fix flip/flop vdso build bug
Date
Two consecutive "make" on an already compiled kernel tree will show
different behavior:

$ make
CALL scripts/checksyscalls.sh
CALL scripts/atomic/check-atomics.sh
DESCEND objtool
CHK include/generated/compile.h
VDSOCHK arch/x86/entry/vdso/vdso64.so.dbg
VDSOCHK arch/x86/entry/vdso/vdso32.so.dbg
Kernel: arch/x86/boot/bzImage is ready (#3)
Building modules, stage 2.
MODPOST 12 modules

$ make
make
CALL scripts/checksyscalls.sh
CALL scripts/atomic/check-atomics.sh
DESCEND objtool
CHK include/generated/compile.h
VDSO arch/x86/entry/vdso/vdso64.so.dbg
OBJCOPY arch/x86/entry/vdso/vdso64.so
VDSO2C arch/x86/entry/vdso/vdso-image-64.c
CC arch/x86/entry/vdso/vdso-image-64.o
VDSO arch/x86/entry/vdso/vdso32.so.dbg
OBJCOPY arch/x86/entry/vdso/vdso32.so
VDSO2C arch/x86/entry/vdso/vdso-image-32.c
CC arch/x86/entry/vdso/vdso-image-32.o
AR arch/x86/entry/vdso/built-in.a
AR arch/x86/entry/built-in.a
AR arch/x86/built-in.a
GEN .version
CHK include/generated/compile.h
UPD include/generated/compile.h
CC init/version.o
AR init/built-in.a
LD vmlinux.o
<snip>

This is causing "LD vmlinux" once every two times even without any
modifications. This is the same bug fixed in commit 92a4728608a8
("x86/boot: Fix if_changed build flip/flop bug"). We cannot use two
"if_changed" in one target. Fix this build bug by merging two commands into
one function.

Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Fixes: 7ac870747988 ("x86/vdso: Switch to generic vDSO implementation")
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
---
arch/x86/entry/vdso/Makefile | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index 39106111be86..34773395139a 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -56,8 +56,7 @@ VDSO_LDFLAGS_vdso.lds = -m elf_x86_64 -soname linux-vdso.so.1 --no-undefined \
-z max-page-size=4096

$(obj)/vdso64.so.dbg: $(obj)/vdso.lds $(vobjs) FORCE
- $(call if_changed,vdso)
- $(call if_changed,vdso_check)
+ $(call if_changed,vdso_and_check)

HOST_EXTRACFLAGS += -I$(srctree)/tools/include -I$(srctree)/include/uapi -I$(srctree)/arch/$(SUBARCH)/include/uapi
hostprogs-y += vdso2c
@@ -127,8 +126,7 @@ $(obj)/%.so: $(obj)/%.so.dbg FORCE
$(call if_changed,objcopy)

$(obj)/vdsox32.so.dbg: $(obj)/vdsox32.lds $(vobjx32s) FORCE
- $(call if_changed,vdso)
- $(call if_changed,vdso_check)
+ $(call if_changed,vdso_and_check)

CPPFLAGS_vdso32.lds = $(CPPFLAGS_vdso.lds)
VDSO_LDFLAGS_vdso32.lds = -m elf_i386 -soname linux-gate.so.1
@@ -167,8 +165,7 @@ $(obj)/vdso32.so.dbg: FORCE \
$(obj)/vdso32/note.o \
$(obj)/vdso32/system_call.o \
$(obj)/vdso32/sigreturn.o
- $(call if_changed,vdso)
- $(call if_changed,vdso_check)
+ $(call if_changed,vdso_and_check)

#
# The DSO images are built using a special linker script.
@@ -184,6 +181,9 @@ VDSO_LDFLAGS = -shared $(call ld-option, --hash-style=both) \
-Bsymbolic
GCOV_PROFILE := n

+quiet_cmd_vdso_and_check = VDSO $@
+ cmd_vdso_and_check = $(cmd_vdso); $(cmd_vdso_check)
+
#
# Install the unstripped copies of vdso*.so. If our toolchain supports
# build-id, install .build-id links as well.
--
2.22.0
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