• Masahiro Yamada's avatar
    kbuild: use -fmacro-prefix-map to make __FILE__ a relative path · a73619a8
    Masahiro Yamada authored
    The __FILE__ macro is used everywhere in the kernel to locate the file
    printing the log message, such as WARN_ON(), etc.  If the kernel is
    built out of tree, this can be a long absolute path, like this:
    
      WARNING: CPU: 1 PID: 1 at /path/to/build/directory/arch/arm64/kernel/foo.c:...
    
    This is because Kbuild runs in the objtree instead of the srctree,
    then __FILE__ is expanded to a file path prefixed with $(srctree)/.
    
    Commit 9da0763b ("kbuild: Use relative path when building in a
    subdir of the source tree") improved this to some extent; $(srctree)
    becomes ".." if the objtree is a child of the srctree.
    
    For other cases of out-of-tree build, __FILE__ is still the absolute
    path.  It also means the kernel image depends on where it was built.
    
    A brand-new option from GCC, -fmacro-prefix-map, solves this problem.
    If your compiler supports it, __FILE__ is the relative path from the
    srctree regardless of O= option.  This provides more readable log and
    more reproducible builds.
    
    Please note __FILE__ is always an absolute path for external modules.
    Signed-off-by: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
    a73619a8
Makefile 61 KB