43d8ce9d65
Introduce in-kernel headers which are made available as an archive through proc (/proc/kheaders.tar.xz file). This archive makes it possible to run eBPF and other tracing programs that need to extend the kernel for tracing purposes without any dependency on the file system having headers. A github PR is sent for the corresponding BCC patch at: https://github.com/iovisor/bcc/pull/2312 On Android and embedded systems, it is common to switch kernels but not have kernel headers available on the file system. Further once a different kernel is booted, any headers stored on the file system will no longer be useful. This is an issue even well known to distros. By storing the headers as a compressed archive within the kernel, we can avoid these issues that have been a hindrance for a long time. The best way to use this feature is by building it in. Several users have a need for this, when they switch debug kernels, they do not want to update the filesystem or worry about it where to store the headers on it. However, the feature is also buildable as a module in case the user desires it not being part of the kernel image. This makes it possible to load and unload the headers from memory on demand. A tracing program can load the module, do its operations, and then unload the module to save kernel memory. The total memory needed is 3.3MB. By having the archive available at a fixed location independent of filesystem dependencies and conventions, all debugging tools can directly refer to the fixed location for the archive, without concerning with where the headers on a typical filesystem which significantly simplifies tooling that needs kernel headers. The code to read the headers is based on /proc/config.gz code and uses the same technique to embed the headers. Other approaches were discussed such as having an in-memory mountable filesystem, but that has drawbacks such as requiring an in-kernel xz decompressor which we don't have today, and requiring usage of 42 MB of kernel memory to host the decompressed headers at anytime. Also this approach is simpler than such approaches. Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
90 lines
2.7 KiB
Bash
Executable File
90 lines
2.7 KiB
Bash
Executable File
#!/bin/bash
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# SPDX-License-Identifier: GPL-2.0
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# This script generates an archive consisting of kernel headers
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# for CONFIG_IKHEADERS_PROC.
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set -e
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spath="$(dirname "$(readlink -f "$0")")"
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kroot="$spath/.."
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outdir="$(pwd)"
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tarfile=$1
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cpio_dir=$outdir/$tarfile.tmp
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# Script filename relative to the kernel source root
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# We add it to the archive because it is small and any changes
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# to this script will also cause a rebuild of the archive.
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sfile="$(realpath --relative-to $kroot "$(readlink -f "$0")")"
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src_file_list="
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include/
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arch/$SRCARCH/include/
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$sfile
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"
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obj_file_list="
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include/
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arch/$SRCARCH/include/
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"
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# Support incremental builds by skipping archive generation
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# if timestamps of files being archived are not changed.
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# This block is useful for debugging the incremental builds.
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# Uncomment it for debugging.
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# iter=1
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# if [ ! -f /tmp/iter ]; then echo 1 > /tmp/iter;
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# else; iter=$(($(cat /tmp/iter) + 1)); fi
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# find $src_file_list -type f | xargs ls -lR > /tmp/src-ls-$iter
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# find $obj_file_list -type f | xargs ls -lR > /tmp/obj-ls-$iter
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# include/generated/compile.h is ignored because it is touched even when none
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# of the source files changed. This causes pointless regeneration, so let us
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# ignore them for md5 calculation.
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pushd $kroot > /dev/null
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src_files_md5="$(find $src_file_list -type f |
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grep -v "include/generated/compile.h" |
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xargs ls -lR | md5sum | cut -d ' ' -f1)"
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popd > /dev/null
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obj_files_md5="$(find $obj_file_list -type f |
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grep -v "include/generated/compile.h" |
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xargs ls -lR | md5sum | cut -d ' ' -f1)"
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if [ -f $tarfile ]; then tarfile_md5="$(md5sum $tarfile | cut -d ' ' -f1)"; fi
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if [ -f kernel/kheaders.md5 ] &&
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[ "$(cat kernel/kheaders.md5|head -1)" == "$src_files_md5" ] &&
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[ "$(cat kernel/kheaders.md5|head -2|tail -1)" == "$obj_files_md5" ] &&
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[ "$(cat kernel/kheaders.md5|tail -1)" == "$tarfile_md5" ]; then
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exit
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fi
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if [ "${quiet}" != "silent_" ]; then
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echo " GEN $tarfile"
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fi
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rm -rf $cpio_dir
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mkdir $cpio_dir
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pushd $kroot > /dev/null
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for f in $src_file_list;
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do find "$f" ! -name "*.cmd" ! -name ".*";
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done | cpio --quiet -pd $cpio_dir
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popd > /dev/null
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# The second CPIO can complain if files already exist which can
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# happen with out of tree builds. Just silence CPIO for now.
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for f in $obj_file_list;
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do find "$f" ! -name "*.cmd" ! -name ".*";
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done | cpio --quiet -pd $cpio_dir >/dev/null 2>&1
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# Remove comments except SDPX lines
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find $cpio_dir -type f -print0 |
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xargs -0 -P8 -n1 perl -pi -e 'BEGIN {undef $/;}; s/\/\*((?!SPDX).)*?\*\///smg;'
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tar -Jcf $tarfile -C $cpio_dir/ . > /dev/null
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echo "$src_files_md5" > kernel/kheaders.md5
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echo "$obj_files_md5" >> kernel/kheaders.md5
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echo "$(md5sum $tarfile | cut -d ' ' -f1)" >> kernel/kheaders.md5
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rm -rf $cpio_dir
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