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    SubjectRe: [PATCH 2/2] locking/atomics: Check atomic headers with sha1sum
    On Mon, Dec 10, 2018 at 05:50:35PM +0000, Mark Rutland wrote:
    > 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 <mark.rutland@arm.com>
    > Cc: Andrew Morton <akpm@linux-foundation.org>
    > Cc: Boqun Feng <boqun.feng@gmail.com>
    > Cc: Ingo Molnar <mingo@kernel.org>
    > Cc: Peter Zijlstra <peterz@infradead.org>
    > Cc: Will Deacon <will.deacon@arm.com>
    > ---
    > include/asm-generic/atomic-instrumented.h | 1 +
    > include/asm-generic/atomic-long.h | 1 +
    > include/linux/atomic-fallback.h | 1 +
    > scripts/atomic/check-atomics.sh | 26 ++++++++++++++++++++------
    > scripts/atomic/gen-atomics.sh | 20 ++++++++++++++++++++
    > 5 files changed, 43 insertions(+), 6 deletions(-)
    > create mode 100755 scripts/atomic/gen-atomics.sh
    >
    > diff --git a/include/asm-generic/atomic-instrumented.h b/include/asm-generic/atomic-instrumented.h
    > index b8f5b35216e1..e8730c6b9fe2 100644
    > --- a/include/asm-generic/atomic-instrumented.h
    > +++ b/include/asm-generic/atomic-instrumented.h
    > @@ -1785,3 +1785,4 @@ atomic64_dec_if_positive(atomic64_t *v)
    > })
    >
    > #endif /* _ASM_GENERIC_ATOMIC_INSTRUMENTED_H */
    > +// b29b625d5de9280f680e42c7be859b55b15e5f6a
    > diff --git a/include/asm-generic/atomic-long.h b/include/asm-generic/atomic-long.h
    > index a833d385a70b..881c7e27af28 100644
    > --- a/include/asm-generic/atomic-long.h
    > +++ b/include/asm-generic/atomic-long.h
    > @@ -1010,3 +1010,4 @@ atomic_long_dec_if_positive(atomic_long_t *v)
    >
    > #endif /* CONFIG_64BIT */
    > #endif /* _ASM_GENERIC_ATOMIC_LONG_H */
    > +// 77558968132ce4f911ad53f6f52ce423006f6268
    > diff --git a/include/linux/atomic-fallback.h b/include/linux/atomic-fallback.h
    > index 1c02c0112fbb..a7d240e465c0 100644
    > --- a/include/linux/atomic-fallback.h
    > +++ b/include/linux/atomic-fallback.h
    > @@ -2292,3 +2292,4 @@ atomic64_dec_if_positive(atomic64_t *v)
    > #define atomic64_cond_read_relaxed(v, c) smp_cond_load_relaxed(&(v)->counter, (c))
    >
    > #endif /* _LINUX_ATOMIC_FALLBACK_H */
    > +// 25de4a2804d70f57e994fe3b419148658bb5378a
    > diff --git a/scripts/atomic/check-atomics.sh b/scripts/atomic/check-atomics.sh
    > index c30101cddf2d..cfa0c2f71c84 100755
    > --- a/scripts/atomic/check-atomics.sh
    > +++ b/scripts/atomic/check-atomics.sh
    > @@ -7,13 +7,27 @@ ATOMICDIR=$(dirname $0)
    > ATOMICTBL=${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%% *}"

    Here we're relying on head and tail being available, but it looks like
    they're also part of coreutils, so that should be fine.

    > +
    > + if [ "${OLDSUM}" != "${NEWSUM}" ]; then
    > + printf "warning: generated include/${header} has been modified.\n"
    > fi
    > done
    > +
    > +exit 0
    > diff --git a/scripts/atomic/gen-atomics.sh b/scripts/atomic/gen-atomics.sh
    > new file mode 100755
    > index 000000000000..27400b0cd732
    > --- /dev/null
    > +++ b/scripts/atomic/gen-atomics.sh
    > @@ -0,0 +1,20 @@
    > +#!/bin/sh
    > +# SPDX-License-Identifier: GPL-2.0
    > +#
    > +# Generate atomic headers
    > +
    > +ATOMICDIR=$(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
    Thanks, this looks sensible to me:

    Acked-by: Will Deacon <will.deacon@arm.com>

    Will

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