• Kees Cook's avatar
    x86/boot: Fix if_changed build flip/flop bug · 92a47286
    Kees Cook authored
    Dirk Gouders reported that two consecutive "make" invocations on an
    already compiled tree will show alternating behaviors:
    
    $ make
      CALL    scripts/checksyscalls.sh
      DESCEND  objtool
      CHK     include/generated/compile.h
      DATAREL arch/x86/boot/compressed/vmlinux
    Kernel: arch/x86/boot/bzImage is ready  (#48)
      Building modules, stage 2.
      MODPOST 165 modules
    
    $ make
      CALL    scripts/checksyscalls.sh
      DESCEND  objtool
      CHK     include/generated/compile.h
      LD      arch/x86/boot/compressed/vmlinux
      ZOFFSET arch/x86/boot/zoffset.h
      AS      arch/x86/boot/header.o
      LD      arch/x86/boot/setup.elf
      OBJCOPY arch/x86/boot/setup.bin
      OBJCOPY arch/x86/boot/vmlinux.bin
      BUILD   arch/x86/boot/bzImage
    Setup is 15644 bytes (padded to 15872 bytes).
    System is 6663 kB
    CRC 3eb90f40
    Kernel: arch/x86/boot/bzImage is ready  (#48)
      Building modules, stage 2.
      MODPOST 165 modules
    
    He bisected it back to:
    
        commit 98f78525 ("x86/boot: Refuse to build with data relocations")
    
    The root cause was the use of the "if_changed" kbuild function multiple
    times for the same target. It was designed to only be used once per
    target, otherwise it will effectively always trigger, flipping back and
    forth between the two commands getting recorded by "if_changed". Instead,
    this patch merges the two commands into a single function to get stable
    build artifacts (i.e. .vmlinux.cmd), and a single build behavior.
    Bisected-and-Reported-by: default avatarDirk Gouders <dirk@gouders.net>
    Fix-Suggested-by: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
    Signed-off-by: default avatarKees Cook <keescook@chromium.org>
    Reviewed-by: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: http://lkml.kernel.org/r/20180724230827.GA37823@beastSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    92a47286
Makefile 5.38 KB