# git rev-parse -q --verify b791d1bdf9212d944d749a5c7ff6febdba241771^{commit}
b791d1bdf9212d944d749a5c7ff6febdba241771
already have revision, skipping fetch
# git checkout -q -f -B kisskb b791d1bdf9212d944d749a5c7ff6febdba241771
# git clean -qxdf
# < git log -1
# commit b791d1bdf9212d944d749a5c7ff6febdba241771
# Merge: 9716e57a0195 1f44328ea24c
# Author: Linus Torvalds <torvalds@linux-foundation.org>
# Date:   Thu Jun 11 18:55:43 2020 -0700
# 
#     Merge tag 'locking-kcsan-2020-06-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
#     
#     Pull the Kernel Concurrency Sanitizer from Thomas Gleixner:
#      "The Kernel Concurrency Sanitizer (KCSAN) is a dynamic race detector,
#       which relies on compile-time instrumentation, and uses a
#       watchpoint-based sampling approach to detect races.
#     
#       The feature was under development for quite some time and has already
#       found legitimate bugs.
#     
#       Unfortunately it comes with a limitation, which was only understood
#       late in the development cycle:
#     
#          It requires an up to date CLANG-11 compiler
#     
#       CLANG-11 is not yet released (scheduled for June), but it's the only
#       compiler today which handles the kernel requirements and especially
#       the annotations of functions to exclude them from KCSAN
#       instrumentation correctly.
#     
#       These annotations really need to work so that low level entry code and
#       especially int3 text poke handling can be completely isolated.
#     
#       A detailed discussion of the requirements and compiler issues can be
#       found here:
#     
#         https://lore.kernel.org/lkml/CANpmjNMTsY_8241bS7=XAfqvZHFLrVEkv_uM4aDUWE_kh3Rvbw@mail.gmail.com/
#     
#       We came to the conclusion that trying to work around compiler
#       limitations and bugs again would end up in a major trainwreck, so
#       requiring a working compiler seemed to be the best choice.
#     
#       For Continous Integration purposes the compiler restriction is
#       manageable and that's where most xxSAN reports come from.
#     
#       For a change this limitation might make GCC people actually look at
#       their bugs. Some issues with CSAN in GCC are 7 years old and one has
#       been 'fixed' 3 years ago with a half baken solution which 'solved' the
#       reported issue but not the underlying problem.
#     
#       The KCSAN developers also ponder to use a GCC plugin to become
#       independent, but that's not something which will show up in a few
#       days.
#     
#       Blocking KCSAN until wide spread compiler support is available is not
#       a really good alternative because the continuous growth of lockless
#       optimizations in the kernel demands proper tooling support"
#     
#     * tag 'locking-kcsan-2020-06-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (76 commits)
#       compiler_types.h, kasan: Use __SANITIZE_ADDRESS__ instead of CONFIG_KASAN to decide inlining
#       compiler.h: Move function attributes to compiler_types.h
#       compiler.h: Avoid nested statement expression in data_race()
#       compiler.h: Remove data_race() and unnecessary checks from {READ,WRITE}_ONCE()
#       kcsan: Update Documentation to change supported compilers
#       kcsan: Remove 'noinline' from __no_kcsan_or_inline
#       kcsan: Pass option tsan-instrument-read-before-write to Clang
#       kcsan: Support distinguishing volatile accesses
#       kcsan: Restrict supported compilers
#       kcsan: Avoid inserting __tsan_func_entry/exit if possible
#       ubsan, kcsan: Don't combine sanitizer with kcov on clang
#       objtool, kcsan: Add kcsan_disable_current() and kcsan_enable_current_nowarn()
#       kcsan: Add __kcsan_{enable,disable}_current() variants
#       checkpatch: Warn about data_race() without comment
#       kcsan: Use GFP_ATOMIC under spin lock
#       Improve KCSAN documentation a bit
#       kcsan: Make reporting aware of KCSAN tests
#       kcsan: Fix function matching in report
#       kcsan: Change data_race() to no longer require marking racing accesses
#       kcsan: Move kcsan_{disable,enable}_current() to kcsan-checks.h
#       ...
# < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-gcc --version
# < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-ld --version
# < git log --format=%s --max-count=1 b791d1bdf9212d944d749a5c7ff6febdba241771
# < make -s -j 24 ARCH=arm O=/kisskb/build/linus_imx_v6_v7_defconfig_arm-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-  imx_v6_v7_defconfig
# < make -s -j 24 ARCH=arm O=/kisskb/build/linus_imx_v6_v7_defconfig_arm-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-  help
# make -s -j 24 ARCH=arm O=/kisskb/build/linus_imx_v6_v7_defconfig_arm-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-  olddefconfig
# make -s -j 24 ARCH=arm O=/kisskb/build/linus_imx_v6_v7_defconfig_arm-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-  
Completed OK
# rm -rf /kisskb/build/linus_imx_v6_v7_defconfig_arm-gcc4.9
# Build took: 0:02:53.901027