locking/atomics: Check atomic headers with sha1sum

We currently check the atomic headers at build-time to ensure they
haven't been modified directly, and these checks require regenerating
the headers in full. As this takes a few seconds, even when
parallelized, this is too slow to run for every kernel build.

Instead, we can generate a hash of each header as we generate them,
which we can cheaply check at build time (~0.16s for all headers).

This patch does so, updating headers with their hashes using the new
gen-atomics.sh script. As some users apparently build the kernel wihout
coreutils, lacking sha1sum, the checks are skipped in this case.
Presumably, most developers have a working coreutils installation.

Signed-off-by: Mark Rutland <[e-mail]>
Acked-by: Will Deacon <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Boqun Feng <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

include/asm-generic/atomic-instrumented.h

···
 })
 
 #endif /* _ASM_GENERIC_ATOMIC_INSTRUMENTED_H */
+// b29b625d5de9280f680e42c7be859b55b15e5f6a

include/asm-generic/atomic-long.h

···
 
 #endif /* CONFIG_64BIT */
 #endif /* _ASM_GENERIC_ATOMIC_LONG_H */
+// 77558968132ce4f911ad53f6f52ce423006f6268

include/linux/atomic-fallback.h

···
 #define atomic64_cond_read_relaxed(v, c) smp_cond_load_relaxed(&(v)->counter, (c))
 
 #endif /* _LINUX_ATOMIC_FALLBACK_H */
+// 25de4a2804d70f57e994fe3b419148658bb5378a

scripts/atomic/check-atomics.sh

···
 ATOMICTBL=${ATOMICDIR}/atomics.tbl
 LINUXDIR=${ATOMICDIR}/../..
 
+echo '' | sha1sum - > /dev/null 2>&1
+if [ $? -ne 0 ]; then
+	printf "sha1sum not available, skipping atomic header checks.\n"
+	exit 0
+fi
+
 cat <<EOF |
-gen-atomic-instrumented.sh      asm-generic/atomic-instrumented.h
-gen-atomic-long.sh              asm-generic/atomic-long.h
-gen-atomic-fallback.sh          linux/atomic-fallback.h
+asm-generic/atomic-instrumented.h
+asm-generic/atomic-long.h
+linux/atomic-fallback.h
 EOF
-while read script header; do
-	if ! (${ATOMICDIR}/${script} ${ATOMICTBL} | diff - ${LINUXDIR}/include/${header} > /dev/null); then
-		printf "warning: include/${header} is out-of-date.\n"
+while read header; do
+	OLDSUM="$(tail -n 1 ${LINUXDIR}/include/${header})"
+	OLDSUM="${OLDSUM#// }"
+
+	NEWSUM="$(head -n -1 ${LINUXDIR}/include/${header} | sha1sum)"
+	NEWSUM="${NEWSUM%% *}"
+
+	if [ "${OLDSUM}" != "${NEWSUM}" ]; then
+		printf "warning: generated include/${header} has been modified.\n"
 	fi
 done
+
+exit 0

scripts/atomic/gen-atomics.sh

···
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Generate atomic headers
+
+ATOMICDIR=$(dirname $0)
+ATOMICTBL=${ATOMICDIR}/atomics.tbl
+LINUXDIR=${ATOMICDIR}/../..
+
+cat <<EOF |
+gen-atomic-instrumented.sh      asm-generic/atomic-instrumented.h
+gen-atomic-long.sh              asm-generic/atomic-long.h
+gen-atomic-fallback.sh          linux/atomic-fallback.h
+EOF
+while read script header; do
+	${ATOMICDIR}/${script} ${ATOMICTBL} > ${LINUXDIR}/include/${header}
+	HASH="$(sha1sum ${LINUXDIR}/include/${header})"
+	HASH="${HASH%% *}"
+	printf "// %s\n" "${HASH}" >> ${LINUXDIR}/include/${header}
+done