linux-kernel - [PATCH] x86/vdso, arm64/vdso: fix flip/flop vdso build bug

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Date:   Fri, 12 Jul 2019 14:43:50 +0900
From:   Naohiro Aota <naohiro.aota@....com>
To:     Vincenzo Frascino <vincenzo.frascino@....com>,
        linux-kernel@...r.kernel.org
Cc:     x86@...nel.org, Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Peter Collingbourne <pcc@...gle.com>,
        Naohiro Aota <naohiro.aota@....com>
Subject: [PATCH] x86/vdso, arm64/vdso: fix flip/flop vdso build bug

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
  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.

Signed-off-by: Naohiro Aota <naohiro.aota@....com>
---
 arch/arm64/kernel/vdso/Makefile |  6 ++++--
 arch/x86/entry/vdso/Makefile    | 12 ++++++------
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
index 4ab863045188..068c614b1231 100644
--- a/arch/arm64/kernel/vdso/Makefile
+++ b/arch/arm64/kernel/vdso/Makefile
@@ -57,8 +57,7 @@ $(obj)/vdso.o : $(obj)/vdso.so
 
 # Link rule for the .so file, .lds has to be first
 $(obj)/vdso.so.dbg: $(obj)/vdso.lds $(obj-vdso) FORCE
-	$(call if_changed,ld)
-	$(call if_changed,vdso_check)
+	$(call if_changed,ld_and_vdso_check)
 
 # Strip rule for the .so file
 $(obj)/%.so: OBJCOPYFLAGS := -S
@@ -77,6 +76,9 @@ include/generated/vdso-offsets.h: $(obj)/vdso.so.dbg FORCE
 quiet_cmd_vdsocc = VDSOCC   $@
       cmd_vdsocc = $(CC) $(a_flags) $(c_flags) -c -o $@ $<
 
+quiet_cmd_ld_and_vdso_check = LD      $@
+      cmd_ld_and_vdso_check = $(cmd_ld); $(cmd_vdso_check)
+
 # Install commands for the unstripped file
 quiet_cmd_vdso_install = INSTALL $@
       cmd_vdso_install = cp $(obj)/$@...g $(MODLIB)/vdso/$@
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