# git rev-parse -q --verify 5cf0fd591f2e7833405bdc7ce2176c3502e8a11e^{commit}
5cf0fd591f2e7833405bdc7ce2176c3502e8a11e
already have revision, skipping fetch
# git checkout -q -f -B kisskb 5cf0fd591f2e7833405bdc7ce2176c3502e8a11e
# git clean -qxdf
# < git log -1
# commit 5cf0fd591f2e7833405bdc7ce2176c3502e8a11e
# Author: Linus Torvalds <torvalds@linux-foundation.org>
# Date:   Tue Feb 23 12:21:58 2021 -0800
# 
#     Kbuild: disable TRIM_UNUSED_KSYMS option
#     
#     The removal of EXPORT_UNUSED_SYMBOL() in commit 367948220fce looks like
#     (and was sold as) a no-op, but it actually had a rather serious and
#     subtle side effect: the UNUSED_SYMBOLS option not only enabled the
#     removed (unused) functionality, it also _disabled_ the TRIM_UNUSED_KSYMS
#     functionality.
#     
#     And it turns out that TRIM_UNUSED_KSYMS is a huge time waste, and takes
#     up a third of the kernel build time for me.  For no actual upside, since
#     no distro is likely to ever be able to enable it (because they all
#     support external kernel modules).
#     
#     Rather than re-enable EXPORT_UNUSED_SYMBOL, this just disables the
#     TRIM_UNUSED_KSYMS option by marking it broken.  I'm tempted to just
#     remove the support entirely, but maybe somebody has a use-case and can
#     fix the behavior of it.
#     
#     I could have just disabled it for COMPILE_TEST, but it really smells
#     like the TRIM_UNUSED_KSYMS option is badly done and not really useful,
#     so this takes the more direct approach - let's see if anybody ever
#     actually notices or complains.
#     
#     Cc: Miroslav Benes <mbenes@suse.cz>
#     Cc: Emil Velikov <emil.l.velikov@gmail.com>
#     Cc: Christoph Hellwig <hch@lst.de>
#     Cc: Jessica Yu <jeyu@kernel.org>
#     Fixes: 367948220fce ("module: remove EXPORT_UNUSED_SYMBOL*")
#     Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
# < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/x86_64-linux/bin/x86_64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/x86_64-linux/bin/x86_64-linux-ld --version
# < git log --format=%s --max-count=1 5cf0fd591f2e7833405bdc7ce2176c3502e8a11e
# < make -s -j 32 ARCH=x86_64 O=/kisskb/build/linus_x86_64-allnoconfig_x86_64-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/x86_64-linux/bin/x86_64-linux-  allnoconfig
# < make -s -j 32 ARCH=x86_64 O=/kisskb/build/linus_x86_64-allnoconfig_x86_64-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/x86_64-linux/bin/x86_64-linux-  help
# make -s -j 32 ARCH=x86_64 O=/kisskb/build/linus_x86_64-allnoconfig_x86_64-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/x86_64-linux/bin/x86_64-linux-  olddefconfig
# make -s -j 32 ARCH=x86_64 O=/kisskb/build/linus_x86_64-allnoconfig_x86_64-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/x86_64-linux/bin/x86_64-linux-  
Completed OK
# rm -rf /kisskb/build/linus_x86_64-allnoconfig_x86_64-gcc4.9
# Build took: 0:00:24.970313