linux-kernel - [PATCH v2 2/2] arm64/vdso: fix flip/flop vdso build bug

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Date:   Fri, 12 Jul 2019 19:15:56 +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 v2 2/2] arm64/vdso: fix flip/flop vdso build bug

Running "make" on an already compiled kernel tree will rebuild the kernel
even without any modifications:

$ make ARCH=arm64 CROSS_COMPILE=/usr/bin/aarch64-unknown-linux-gnu-
arch/arm64/Makefile:58: CROSS_COMPILE_COMPAT not defined or empty, the compat vDSO will not be built
  CALL    scripts/checksyscalls.sh
  CALL    scripts/atomic/check-atomics.sh
  VDSOCHK arch/arm64/kernel/vdso/vdso.so.dbg
  VDSOSYM include/generated/vdso-offsets.h
  CHK     include/generated/compile.h
  CC      arch/arm64/kernel/signal.o
  CC      arch/arm64/kernel/vdso.o
  CC      arch/arm64/kernel/signal32.o
  LD      arch/arm64/kernel/vdso/vdso.so.dbg
  OBJCOPY arch/arm64/kernel/vdso/vdso.so
  AS      arch/arm64/kernel/vdso/vdso.o
  AR      arch/arm64/kernel/vdso/built-in.a
  AR      arch/arm64/kernel/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

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@...ionext.com>
Fixes: 28b1a824a4f4 ("arm64: vdso: Substitute gettimeofday() with C implementation")
Signed-off-by: Naohiro Aota <naohiro.aota@....com>
---
 arch/arm64/kernel/vdso/Makefile | 6 ++++--
 1 file changed, 4 insertions(+), 2 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 $(MODLIB)/vdso/$@
-- 
2.22.0