# git rev-parse -q --verify 335aca5f65f1a39670944930131da5f2276f888f^{commit}
335aca5f65f1a39670944930131da5f2276f888f
already have revision, skipping fetch
# git checkout -q -f -B kisskb 335aca5f65f1a39670944930131da5f2276f888f
# git clean -qxdf
# < git log -1
# commit 335aca5f65f1a39670944930131da5f2276f888f
# Merge: 8ac9b9d61f0e 7fa95f9adaee
# Author: Michael Ellerman <mpe@ellerman.id.au>
# Date:   Thu Jul 23 17:43:44 2020 +1000
# 
#     Merge branch 'scv' support into next
#     
#     From Nick's cover letter:
#     
#     Linux powerpc new system call instruction and ABI
#     
#     System Call Vectored (scv) ABI
#     ==============================
#     
#     The scv instruction is introduced with POWER9 / ISA3, it comes with an
#     rfscv counter-part. The benefit of these instructions is
#     performance (trading slower SRR0/1 with faster LR/CTR registers, and
#     entering the kernel with MSR[EE] and MSR[RI] left enabled, which can
#     reduce MSR updates. The scv instruction has 128 levels (not enough to
#     cover the Linux system call space).
#     
#     Assignment and advertisement
#     ----------------------------
#     The proposal is to assign scv levels conservatively, and advertise
#     them with HWCAP feature bits as we add support for more.
#     
#     Linux has not enabled FSCR[SCV] yet, so executing the scv instruction
#     will cause the kernel to log a "SCV facility unavilable" message, and
#     deliver a SIGILL with ILL_ILLOPC to the process. Linux has defined a
#     HWCAP2 bit PPC_FEATURE2_SCV for SCV support, but does not set it.
#     
#     This change allocates the zero level ('scv 0'), advertised with
#     PPC_FEATURE2_SCV, which will be used to provide normal Linux system
#     calls (equivalent to 'sc').
#     
#     Attempting to execute scv with other levels will cause a SIGILL to be
#     delivered the same as before, but will not log a "SCV facility
#     unavailable" message (because the processor facility is enabled).
#     
#     Calling convention
#     ------------------
#     The proposal is for scv 0 to provide the standard Linux system call
#     ABI with the following differences from sc convention[1]:
#     
#     - LR is to be volatile across scv calls. This is necessary because the
#       scv instruction clobbers LR. From previous discussion, this should
#       be possible to deal with in GCC clobbers and CFI.
#     
#     - cr1 and cr5-cr7 are volatile. This matches the C ABI and would allow
#       the kernel system call exit to avoid restoring the volatile cr
#       registers (although we probably still would anyway to avoid
#       information leaks).
#     
#     - Error handling: The consensus among kernel, glibc, and musl is to
#       move to using negative return values in r3 rather than CR0[SO]=1 to
#       indicate error, which matches most other architectures, and is
#       closer to a function call.
#     
#     Notes
#     -----
#     - r0,r4-r8 are documented as volatile in the ABI, but the kernel patch
#       as submitted currently preserves them. This is to leave room for
#       deciding which way to go with these. Some small benefit was found by
#       preserving them[1] but I'm not convinced it's worth deviating from
#       the C function call ABI just for this. Release code should follow
#       the ABI.
#     
#     Previous discussions:
#     https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-April/208691.html
#     https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-April/209268.html
#     
#     [1] https://github.com/torvalds/linux/blob/master/Documentation/powerpc/syscall64-abi.rst
#     [2] https://lists.ozlabs.org/pipermail/linuxppc-dev/2020-April/209263.html
# < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-ld --version
# < git log --format=%s --max-count=1 335aca5f65f1a39670944930131da5f2276f888f
# < make -s -j 80 ARCH=powerpc O=/kisskb/build/powerpc-next_pseries_defconfig+FA_DUMP_powerpc-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-  pseries_defconfig
# Added to kconfig CONFIG_CRASH_DUMP=y
# Added to kconfig CONFIG_FA_DUMP=y
# < make -s -j 80 ARCH=powerpc O=/kisskb/build/powerpc-next_pseries_defconfig+FA_DUMP_powerpc-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-  help
# make -s -j 80 ARCH=powerpc O=/kisskb/build/powerpc-next_pseries_defconfig+FA_DUMP_powerpc-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-  olddefconfig
.config:4026:warning: override: reassigning to symbol CRASH_DUMP
.config:4027:warning: override: reassigning to symbol FA_DUMP
# make -s -j 80 ARCH=powerpc O=/kisskb/build/powerpc-next_pseries_defconfig+FA_DUMP_powerpc-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/powerpc64-linux/bin/powerpc64-linux-  
Completed OK
# rm -rf /kisskb/build/powerpc-next_pseries_defconfig+FA_DUMP_powerpc-gcc4.9
# Build took: 0:03:13.694742