# git rev-parse -q --verify bc13f05ffaf016d42536571c2e9173f85cefd47a^{commit}
bc13f05ffaf016d42536571c2e9173f85cefd47a
already have revision, skipping fetch
# git checkout -q -f -B kisskb bc13f05ffaf016d42536571c2e9173f85cefd47a
# git clean -qxdf
# < git log -1
# commit bc13f05ffaf016d42536571c2e9173f85cefd47a
# Author: Michael Ellerman <mpe@ellerman.id.au>
# Date:   Thu Feb 14 11:08:29 2019 +1100
# 
#     powerpc/ptrace: Simplify vr_get/set() to avoid GCC warning
#     
#     GCC 8 warns about the logic in vr_get/set(), which with -Werror breaks
#     the build:
#     
#       In function ‘user_regset_copyin’,
#           inlined from ‘vr_set’ at arch/powerpc/kernel/ptrace.c:628:9:
#       include/linux/regset.h:295:4: error: ‘memcpy’ offset [-527, -529] is
#       out of the bounds [0, 16] of object ‘vrsave’ with type ‘union
#       <anonymous>’ [-Werror=array-bounds]
#       arch/powerpc/kernel/ptrace.c: In function ‘vr_set’:
#       arch/powerpc/kernel/ptrace.c:623:5: note: ‘vrsave’ declared here
#          } vrsave;
#     
#     This has been identified as a regression in GCC, see GCC bug 88273.
#     
#     However we can avoid the warning and also simplify the logic and make
#     it more robust.
#     
#     Currently we pass -1 as end_pos to user_regset_copyout(). This says
#     "copy up to the end of the regset".
#     
#     The definition of the regset is:
#             [REGSET_VMX] = {
#                     .core_note_type = NT_PPC_VMX, .n = 34,
#                     .size = sizeof(vector128), .align = sizeof(vector128),
#                     .active = vr_active, .get = vr_get, .set = vr_set
#             },
#     
#     The end is calculated as (n * size), ie. 34 * sizeof(vector128).
#     
#     In vr_get/set() we pass start_pos as 33 * sizeof(vector128), meaning
#     we can copy up to sizeof(vector128) into/out-of vrsave.
#     
#     The on-stack vrsave is defined as:
#       union {
#               elf_vrreg_t reg;
#               u32 word;
#       } vrsave;
#     
#     And elf_vrreg_t is:
#       typedef __vector128 elf_vrreg_t;
#     
#     So there is no bug, but we rely on all those sizes lining up,
#     otherwise we would have a kernel stack exposure/overwrite on our
#     hands.
#     
#     Rather than relying on that we can pass an explict end_pos based on
#     the sizeof(vrsave). The result should be exactly the same but it's
#     more obviously not over-reading/writing the stack and it avoids the
#     compiler warning.
#     
#     Reported-by: Meelis Roos <mroos@linux.ee>
#     Reported-by: Mathieu Malaterre <malat@debian.org>
#     Cc: stable@vger.kernel.org
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
# < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version
# < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/powerpc64-linux/bin/powerpc64-linux-ld --version
# < git log --format=%s --max-count=1 bc13f05ffaf016d42536571c2e9173f85cefd47a
# < make -s -j 120 ARCH=powerpc O=/kisskb/build/powerpc-next-rand_powernv_defconfig+NO_RADIX_powerpc-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  powernv_defconfig
# Added to kconfig CONFIG_PPC_RADIX_MMU=n
# yes \n | make -s -j 120 ARCH=powerpc O=/kisskb/build/powerpc-next-rand_powernv_defconfig+NO_RADIX_powerpc-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  oldconfig
yes: standard output: Broken pipe
# make -s -j 120 ARCH=powerpc O=/kisskb/build/powerpc-next-rand_powernv_defconfig+NO_RADIX_powerpc-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  
WARNING: modpost: Found 2 section mismatch(es).
To see full details build your kernel with:
'make CONFIG_DEBUG_SECTION_MISMATCH=y'
Completed OK
# rm -rf /kisskb/build/powerpc-next-rand_powernv_defconfig+NO_RADIX_powerpc-gcc8
# Build took: 0:01:48.532846