# git rev-parse -q --verify a88603f4b92ecef9e2359e40bcb99ad399d85dd7^{commit}
a88603f4b92ecef9e2359e40bcb99ad399d85dd7
already have revision, skipping fetch
# git checkout -q -f -B kisskb a88603f4b92ecef9e2359e40bcb99ad399d85dd7
# git clean -qxdf
# < git log -1
# commit a88603f4b92ecef9e2359e40bcb99ad399d85dd7
# Author: Michael Ellerman <mpe@ellerman.id.au>
# Date:   Thu Jul 29 22:56:36 2021 +1000
# 
#     powerpc/vdso: Don't use r30 to avoid breaking Go lang
#     
#     The Go runtime uses r30 for some special value called 'g'. It assumes
#     that value will remain unchanged even when calling VDSO functions.
#     Although r30 is non-volatile across function calls, the callee is free
#     to use it, as long as the callee saves the value and restores it before
#     returning.
#     
#     It used to be true by accident that the VDSO didn't use r30, because the
#     VDSO was hand-written asm. When we switched to building the VDSO from C
#     the compiler started using r30, at least in some builds, leading to
#     crashes in Go. eg:
#     
#       ~/go/src$ ./all.bash
#       Building Go cmd/dist using /usr/lib/go-1.16. (go1.16.2 linux/ppc64le)
#       Building Go toolchain1 using /usr/lib/go-1.16.
#       go build os/exec: /usr/lib/go-1.16/pkg/tool/linux_ppc64le/compile: signal: segmentation fault
#       go build reflect: /usr/lib/go-1.16/pkg/tool/linux_ppc64le/compile: signal: segmentation fault
#       go tool dist: FAILED: /usr/lib/go-1.16/bin/go install -gcflags=-l -tags=math_big_pure_go compiler_bootstrap bootstrap/cmd/...: exit status 1
#     
#     There are patches in flight to fix Go[1], but until they are released
#     and widely deployed we can workaround it in the VDSO by avoiding use of
#     r30.
#     
#     Note this only works with GCC, clang does not support -ffixed-rN.
#     
#     1: https://go-review.googlesource.com/c/go/+/328110
#     
#     Fixes: ab037dd87a2f ("powerpc/vdso: Switch VDSO to generic C implementation.")
#     Cc: stable@vger.kernel.org # v5.11+
#     Reported-by: Paul Menzel <pmenzel@molgen.mpg.de>
#     Tested-by: Paul Menzel <pmenzel@molgen.mpg.de>
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
#     Link: https://lore.kernel.org/r/20210729131244.2595519-1-mpe@ellerman.id.au
# < /opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-ld --version
# < git log --format=%s --max-count=1 a88603f4b92ecef9e2359e40bcb99ad399d85dd7
# < make -s -j 32 ARCH=powerpc O=/kisskb/build/powerpc-fixes_40x_walnut_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  40x/walnut_defconfig
# < make -s -j 32 ARCH=powerpc O=/kisskb/build/powerpc-fixes_40x_walnut_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  help
# make -s -j 32 ARCH=powerpc O=/kisskb/build/powerpc-fixes_40x_walnut_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  olddefconfig
# make -s -j 32 ARCH=powerpc O=/kisskb/build/powerpc-fixes_40x_walnut_defconfig_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  
Completed OK
# rm -rf /kisskb/build/powerpc-fixes_40x_walnut_defconfig_powerpc-gcc5
# Build took: 0:00:26.687635