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.
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| @@ -16,16 +16,21 @@ the kernel may be unreproducible, and how to avoid them. · 15 unmodified lines | ||
| 16 | 16 | Timestamps |
| 17 | 17 | ---------- |
| 18 | 18 | |
| 19 | −The kernel embeds a timestamp in two places: | |
| 19 | +The kernel embeds timestamps in three places: | |
| 20 | 20 | |
| 21 | 21 | * The version string exposed by ``uname()`` and included in |
| 22 | 22 | ``/proc/version`` |
| 23 | 23 | |
| 24 | 24 | * File timestamps in the embedded initramfs |
| 25 | 25 | |
| 26 | −By default the timestamp is the current time. This must be overridden | |
| 27 | −using the `KBUILD_BUILD_TIMESTAMP`_ variable. If you are building | |
| 28 | −from a git commit, you could use its commit date. | |
| 26 | +* If enabled via ``CONFIG_IKHEADERS``, file timestamps of kernel | |
| 27 | + headers embedded in the kernel or respective module, | |
| 28 | + exposed via ``/sys/kernel/kheaders.tar.xz`` | |
| 29 | + | |
| 30 | +By default the timestamp is the current time and in the case of | |
| 31 | +``kheaders`` the various files' modification times. This must | |
| 32 | +be overridden using the `KBUILD_BUILD_TIMESTAMP`_ variable. | |
| 33 | +If you are building from a git commit, you could use its commit date. | |
| 29 | 34 | |
| 30 | 35 | The kernel does *not* use the ``__DATE__`` and ``__TIME__`` macros, |
| 31 | 36 | and enables warnings if they are used. If you incorporate external |
| @@ -71,7 +71,10 @@ done | cpio --quiet -pd $cpio_dir >/dev/null 2>&1 · 70 unmodified lines | ||
| 71 | 71 | find $cpio_dir -type f -print0 | |
| 72 | 72 | xargs -0 -P8 -n1 perl -pi -e 'BEGIN {undef $/;}; s/\/\*((?!SPDX).)*?\*\///smg;' |
| 73 | 73 | |
| 74 | −tar -Jcf $tarfile -C $cpio_dir/ . > /dev/null | |
| 74 | +# Create archive and try to normalize metadata for reproducibility | |
| 75 | +tar "${KBUILD_BUILD_TIMESTAMP:+--mtime=$KBUILD_BUILD_TIMESTAMP}" \ | |
| 76 | + --owner=0 --group=0 --sort=name --numeric-owner \ | |
| 77 | + -Jcf $tarfile -C $cpio_dir/ . > /dev/null | |
| 75 | 78 | |
| 76 | 79 | echo "$src_files_md5" > kernel/kheaders.md5 |
| 77 | 80 | echo "$obj_files_md5" >> kernel/kheaders.md5 |