path: root/Documentation/kbuild/reproducible-builds.rst
diff options
authorDmitry Goldin <>2019-10-04 10:40:07 +0000
committerMasahiro Yamada <>2019-10-05 15:29:49 +0900
commit86cdd2fdc4e39c388d39c7ba2396d1a9dfd66226 (patch)
treec79544ad48bd9dedb9893a7c2d5c388a9ed5dfba /Documentation/kbuild/reproducible-builds.rst
parentd188b8c901bb4966ab035ce90af02426f062e9e1 (diff)
kheaders: make headers archive reproducible
In commit 43d8ce9d65a5 ("Provide in-kernel headers to make extending kernel easier") a new mechanism was introduced, for kernels >=5.2, which embeds the kernel headers in the kernel image or a module and exposes them in procfs for use by userland tools. The archive containing the header files has nondeterminism caused by header files metadata. This patch normalizes the metadata and utilizes KBUILD_BUILD_TIMESTAMP if provided and otherwise falls back to the default behaviour. In commit f7b101d33046 ("kheaders: Move from proc to sysfs") it was modified to use sysfs and the script for generation of the archive was renamed to what is being patched. Signed-off-by: Dmitry Goldin <> Reviewed-by: Greg Kroah-Hartman <> Reviewed-by: Joel Fernandes (Google) <> Signed-off-by: Masahiro Yamada <>
Diffstat (limited to 'Documentation/kbuild/reproducible-builds.rst')
1 files changed, 9 insertions, 4 deletions
diff --git a/Documentation/kbuild/reproducible-builds.rst b/Documentation/kbuild/reproducible-builds.rst
index ab92e98c89c8..503393854e2e 100644
--- a/Documentation/kbuild/reproducible-builds.rst
+++ b/Documentation/kbuild/reproducible-builds.rst
@@ -16,16 +16,21 @@ the kernel may be unreproducible, and how to avoid them.
-The kernel embeds a timestamp in two places:
+The kernel embeds timestamps in three places:
* The version string exposed by ``uname()`` and included in
* File timestamps in the embedded initramfs
-By default the timestamp is the current time. This must be overridden
-using the `KBUILD_BUILD_TIMESTAMP`_ variable. If you are building
-from a git commit, you could use its commit date.
+* If enabled via ``CONFIG_IKHEADERS``, file timestamps of kernel
+ headers embedded in the kernel or respective module,
+ exposed via ``/sys/kernel/kheaders.tar.xz``
+By default the timestamp is the current time and in the case of
+``kheaders`` the various files' modification times. This must
+be overridden using the `KBUILD_BUILD_TIMESTAMP`_ variable.
+If you are building from a git commit, you could use its commit date.
The kernel does *not* use the ``__DATE__`` and ``__TIME__`` macros,
and enables warnings if they are used. If you incorporate external