Re: [PATCH] kbuild: use -fmacro-prefix-map to make __FILE__ a relative path

[Sascha Hauer <s.hauer@pengutronix.de>]

On Thu, Aug 08, 2019 at 01:48:08AM +0900, Masahiro Yamada wrote:
> Linux commit a73619a845d5625079cc1b3b820f44c899618388
> 
> 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 9da0763bdd82 ("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: Masahiro Yamada <yamada.masahiro@socionext.com>
> ---
>  Makefile | 3 +++
>  1 file changed, 3 insertions(+)

Applied, thanks

Sascha

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