[PATCH] Revert kheaders feature

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

Now that BPF does not need a copy of the kernel headers anymore in order
to build programs, there's no real need for putting the kernel headers
into a kernel module.  So drop the feature quick, before someone starts
using it :)

This patch reverts the following commits:
f276031b4e2f ("kheaders: explain why include/config/autoconf.h is excluded from md5sum")
1463f74f492e ("kheaders: remove the last bashism to allow sh to run it")
ea79e5168be6 ("kheaders: optimize header copy for in-tree builds")
0e11773e7609 ("kheaders: optimize md5sum calculation for in-tree builds")
9a0663571844 ("kheaders: remove unneeded 'cat' command piped to 'head' / 'tail'")
700dea5a0bea ("kheaders: substituting --sort in archive creation")
86cdd2fdc4e3 ("kheaders: make headers archive reproducible")
7199ff7d7400 ("kheaders: include only headers into kheaders_data.tar.xz")
b60b7c2ea9b7 ("kheaders: remove meaningless -R option of 'ls'")
1457dc9ed8da ("kheaders: Do not regenerate archive if config is not changed")
f7b101d33046 ("kheaders: Move from proc to sysfs")
43d8ce9d65a5 ("Provide in-kernel headers to make extending kernel easier")

Reported-by: Olof Johansson <olof.johansson@gmail.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Michal Marek <michal.lkml@markovi.net>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Patrick Bellasi <patrick.bellasi@arm.com>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: linux-kbuild@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

This came up in a bpf presentation today, along with talking with Olof.
Anyone object to ripping this out before people start to rely on it, now
that it's stated reason isn't needed anymore?


 Documentation/kbuild/reproducible-builds.rst | 13 +--
 init/Kconfig                                 |  9 --
 kernel/.gitignore                            |  1 -
 kernel/Makefile                              | 10 --
 kernel/gen_kheaders.sh                       | 97 --------------------
 kernel/kheaders.c                            | 66 -------------
 6 files changed, 4 insertions(+), 192 deletions(-)
 delete mode 100755 kernel/gen_kheaders.sh
 delete mode 100644 kernel/kheaders.c

diff --git a/Documentation/kbuild/reproducible-builds.rst b/Documentation/kbuild/reproducible-builds.rst
index 503393854e2e..ab92e98c89c8 100644
--- a/Documentation/kbuild/reproducible-builds.rst
+++ b/Documentation/kbuild/reproducible-builds.rst
@@ -16,21 +16,16 @@ the kernel may be unreproducible, and how to avoid them.
 Timestamps
 ----------
 
-The kernel embeds timestamps in three places:
+The kernel embeds a timestamp in two places:
 
 * The version string exposed by ``uname()`` and included in
   ``/proc/version``
 
 * File timestamps in the embedded initramfs
 
-* 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.
+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.
 
 The kernel does *not* use the ``__DATE__`` and ``__TIME__`` macros,
 and enables warnings if they are used.  If you incorporate external
diff --git a/init/Kconfig b/init/Kconfig
index 24b23d843df1..da5dea21b9cb 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -599,15 +599,6 @@ config IKCONFIG_PROC
 	  This option enables access to the kernel configuration file
 	  through /proc/config.gz.
 
-config IKHEADERS
-	tristate "Enable kernel headers through /sys/kernel/kheaders.tar.xz"
-	depends on SYSFS
-	help
-	  This option enables access to the in-kernel headers that are generated during
-	  the build process. These can be used to build eBPF tracing programs,
-	  or similar programs.  If you build the headers as a module, a module called
-	  kheaders.ko is built which can be loaded on-demand to get access to headers.
-
 config LOG_BUF_SHIFT
 	int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
 	range 12 25
diff --git a/kernel/.gitignore b/kernel/.gitignore
index 34d1e77ee9df..6e699100872f 100644
--- a/kernel/.gitignore
+++ b/kernel/.gitignore
@@ -1,6 +1,5 @@
 #
 # Generated files
 #
-kheaders.md5
 timeconst.h
 hz.bc
diff --git a/kernel/Makefile b/kernel/Makefile
index 4cb4130ced32..9ea0a49bd856 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -74,7 +74,6 @@ obj-$(CONFIG_UTS_NS) += utsname.o
 obj-$(CONFIG_USER_NS) += user_namespace.o
 obj-$(CONFIG_PID_NS) += pid_namespace.o
 obj-$(CONFIG_IKCONFIG) += configs.o
-obj-$(CONFIG_IKHEADERS) += kheaders.o
 obj-$(CONFIG_SMP) += stop_machine.o
 obj-$(CONFIG_KPROBES_SANITY_TEST) += test_kprobes.o
 obj-$(CONFIG_AUDIT) += audit.o auditfilter.o
@@ -127,12 +126,3 @@ $(obj)/configs.o: $(obj)/config_data.gz
 targets += config_data.gz
 $(obj)/config_data.gz: $(KCONFIG_CONFIG) FORCE
 	$(call if_changed,gzip)
-
-$(obj)/kheaders.o: $(obj)/kheaders_data.tar.xz
-
-quiet_cmd_genikh = CHK     $(obj)/kheaders_data.tar.xz
-      cmd_genikh = $(CONFIG_SHELL) $(srctree)/kernel/gen_kheaders.sh $@
-$(obj)/kheaders_data.tar.xz: FORCE
-	$(call cmd,genikh)
-
-clean-files := kheaders_data.tar.xz kheaders.md5
diff --git a/kernel/gen_kheaders.sh b/kernel/gen_kheaders.sh
deleted file mode 100755
index e13ca842eb7e..000000000000
--- a/kernel/gen_kheaders.sh
+++ /dev/null
@@ -1,97 +0,0 @@
-#!/bin/sh
-# SPDX-License-Identifier: GPL-2.0
-
-# This script generates an archive consisting of kernel headers
-# for CONFIG_IKHEADERS.
-set -e
-sfile="$(readlink -f "$0")"
-outdir="$(pwd)"
-tarfile=$1
-cpio_dir=$outdir/$tarfile.tmp
-
-dir_list="
-include/
-arch/$SRCARCH/include/
-"
-
-# Support incremental builds by skipping archive generation
-# if timestamps of files being archived are not changed.
-
-# This block is useful for debugging the incremental builds.
-# Uncomment it for debugging.
-# if [ ! -f /tmp/iter ]; then iter=1; echo 1 > /tmp/iter;
-# else iter=$(($(cat /tmp/iter) + 1)); echo $iter > /tmp/iter; fi
-# find $all_dirs -name "*.h" | xargs ls -l > /tmp/ls-$iter
-
-all_dirs=
-if [ "$building_out_of_srctree" ]; then
-	for d in $dir_list; do
-		all_dirs="$all_dirs $srctree/$d"
-	done
-fi
-all_dirs="$all_dirs $dir_list"
-
-# include/generated/compile.h is ignored because it is touched even when none
-# of the source files changed.
-#
-# When Kconfig regenerates include/generated/autoconf.h, its timestamp is
-# updated, but the contents might be still the same. When any CONFIG option is
-# changed, Kconfig touches the corresponding timestamp file include/config/*.h.
-# Hence, the md5sum detects the configuration change anyway. We do not need to
-# check include/generated/autoconf.h explicitly.
-#
-# Ignore them for md5 calculation to avoid pointless regeneration.
-headers_md5="$(find $all_dirs -name "*.h"			|
-		grep -v "include/generated/compile.h"	|
-		grep -v "include/generated/autoconf.h"	|
-		xargs ls -l | md5sum | cut -d ' ' -f1)"
-
-# Any changes to this script will also cause a rebuild of the archive.
-this_file_md5="$(ls -l $sfile | md5sum | cut -d ' ' -f1)"
-if [ -f $tarfile ]; then tarfile_md5="$(md5sum $tarfile | cut -d ' ' -f1)"; fi
-if [ -f kernel/kheaders.md5 ] &&
-	[ "$(head -n 1 kernel/kheaders.md5)" = "$headers_md5" ] &&
-	[ "$(head -n 2 kernel/kheaders.md5 | tail -n 1)" = "$this_file_md5" ] &&
-	[ "$(tail -n 1 kernel/kheaders.md5)" = "$tarfile_md5" ]; then
-		exit
-fi
-
-if [ "${quiet}" != "silent_" ]; then
-       echo "  GEN     $tarfile"
-fi
-
-rm -rf $cpio_dir
-mkdir $cpio_dir
-
-if [ "$building_out_of_srctree" ]; then
-	(
-		cd $srctree
-		for f in $dir_list
-			do find "$f" -name "*.h";
-		done | cpio --quiet -pd $cpio_dir
-	)
-fi
-
-# The second CPIO can complain if files already exist which can happen with out
-# of tree builds having stale headers in srctree. Just silence CPIO for now.
-for f in $dir_list;
-	do find "$f" -name "*.h";
-done | cpio --quiet -pd $cpio_dir >/dev/null 2>&1
-
-# Remove comments except SDPX lines
-find $cpio_dir -type f -print0 |
-	xargs -0 -P8 -n1 perl -pi -e 'BEGIN {undef $/;}; s/\/\*((?!SPDX).)*?\*\///smg;'
-
-# Create archive and try to normalize metadata for reproducibility.
-# For compatibility with older versions of tar, files are fed to tar
-# pre-sorted, as --sort=name might not be available.
-find $cpio_dir -printf "./%P\n" | LC_ALL=C sort | \
-    tar "${KBUILD_BUILD_TIMESTAMP:+--mtime=$KBUILD_BUILD_TIMESTAMP}" \
-    --owner=0 --group=0 --numeric-owner --no-recursion \
-    -Jcf $tarfile -C $cpio_dir/ -T - > /dev/null
-
-echo $headers_md5 > kernel/kheaders.md5
-echo "$this_file_md5" >> kernel/kheaders.md5
-echo "$(md5sum $tarfile | cut -d ' ' -f1)" >> kernel/kheaders.md5
-
-rm -rf $cpio_dir
diff --git a/kernel/kheaders.c b/kernel/kheaders.c
deleted file mode 100644
index 8f69772af77b..000000000000
--- a/kernel/kheaders.c
+++ /dev/null
@@ -1,66 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/*
- * Provide kernel headers useful to build tracing programs
- * such as for running eBPF tracing tools.
- *
- * (Borrowed code from kernel/configs.c)
- */
-
-#include <linux/kernel.h>
-#include <linux/module.h>
-#include <linux/kobject.h>
-#include <linux/init.h>
-
-/*
- * Define kernel_headers_data and kernel_headers_data_end, within which the
- * compressed kernel headers are stored. The file is first compressed with xz.
- */
-
-asm (
-"	.pushsection .rodata, \"a\"		\n"
-"	.global kernel_headers_data		\n"
-"kernel_headers_data:				\n"
-"	.incbin \"kernel/kheaders_data.tar.xz\"	\n"
-"	.global kernel_headers_data_end		\n"
-"kernel_headers_data_end:			\n"
-"	.popsection				\n"
-);
-
-extern char kernel_headers_data;
-extern char kernel_headers_data_end;
-
-static ssize_t
-ikheaders_read(struct file *file,  struct kobject *kobj,
-	       struct bin_attribute *bin_attr,
-	       char *buf, loff_t off, size_t len)
-{
-	memcpy(buf, &kernel_headers_data + off, len);
-	return len;
-}
-
-static struct bin_attribute kheaders_attr __ro_after_init = {
-	.attr = {
-		.name = "kheaders.tar.xz",
-		.mode = 0444,
-	},
-	.read = &ikheaders_read,
-};
-
-static int __init ikheaders_init(void)
-{
-	kheaders_attr.size = (&kernel_headers_data_end -
-			      &kernel_headers_data);
-	return sysfs_create_bin_file(kernel_kobj, &kheaders_attr);
-}
-
-static void __exit ikheaders_cleanup(void)
-{
-	sysfs_remove_bin_file(kernel_kobj, &kheaders_attr);
-}
-
-module_init(ikheaders_init);
-module_exit(ikheaders_cleanup);
-
-MODULE_LICENSE("GPL v2");
-MODULE_AUTHOR("Joel Fernandes");
-MODULE_DESCRIPTION("Echo the kernel header artifacts used to build the kernel");
-- 
2.25.0