linux-kernel - [PATCH 4.14 52/62] kbuild: use -fmacro-prefix-map to make __FILE_

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri,  8 Nov 2019 19:50:40 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.14 52/62] kbuild: use -fmacro-prefix-map to make __FILE__ a relative path

From: Masahiro Yamada <yamada.masahiro@...ionext.com>

[ Upstream 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@...ionext.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Makefile b/Makefile
index 1d7f47334ca2b..61660387eb34b 100644
--- a/Makefile
+++ b/Makefile
@@ -840,6 +840,9 @@ KBUILD_CFLAGS   += $(call cc-option,-Werror=incompatible-pointer-types)
 # Require designated initializers for all marked structures
 KBUILD_CFLAGS   += $(call cc-option,-Werror=designated-init)

+# change __FILE__ to the relative path from the srctree
+KBUILD_CFLAGS	+= $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
+
 # use the deterministic mode of AR if available
 KBUILD_ARFLAGS := $(call ar-option,D)

-- 
2.20.1