# git rev-parse -q --verify 41a506ef71eb38d94fe133f565c87c3e06ccc072^{commit}
41a506ef71eb38d94fe133f565c87c3e06ccc072
already have revision, skipping fetch
# git checkout -q -f -B kisskb 41a506ef71eb38d94fe133f565c87c3e06ccc072
# git clean -qxdf
# < git log -1
# commit 41a506ef71eb38d94fe133f565c87c3e06ccc072
# Author: Naveen N Rao <naveen@kernel.org>
# Date:   Wed Jun 21 10:43:49 2023 +0530
# 
#     powerpc/ftrace: Create a dummy stackframe to fix stack unwind
#     
#     With ppc64 -mprofile-kernel and ppc32 -pg, profiling instructions to
#     call into ftrace are emitted right at function entry. The instruction
#     sequence used is minimal to reduce overhead. Crucially, a stackframe is
#     not created for the function being traced. This breaks stack unwinding
#     since the function being traced does not have a stackframe for itself.
#     As such, it never shows up in the backtrace:
#     
#     /sys/kernel/debug/tracing # echo 1 > /proc/sys/kernel/stack_tracer_enabled
#     /sys/kernel/debug/tracing # cat stack_trace
#             Depth    Size   Location    (17 entries)
#             -----    ----   --------
#       0)     4144      32   ftrace_call+0x4/0x44
#       1)     4112     432   get_page_from_freelist+0x26c/0x1ad0
#       2)     3680     496   __alloc_pages+0x290/0x1280
#       3)     3184     336   __folio_alloc+0x34/0x90
#       4)     2848     176   vma_alloc_folio+0xd8/0x540
#       5)     2672     272   __handle_mm_fault+0x700/0x1cc0
#       6)     2400     208   handle_mm_fault+0xf0/0x3f0
#       7)     2192      80   ___do_page_fault+0x3e4/0xbe0
#       8)     2112     160   do_page_fault+0x30/0xc0
#       9)     1952     256   data_access_common_virt+0x210/0x220
#      10)     1696     400   0xc00000000f16b100
#      11)     1296     384   load_elf_binary+0x804/0x1b80
#      12)      912     208   bprm_execve+0x2d8/0x7e0
#      13)      704      64   do_execveat_common+0x1d0/0x2f0
#      14)      640     160   sys_execve+0x54/0x70
#      15)      480      64   system_call_exception+0x138/0x350
#      16)      416     416   system_call_common+0x160/0x2c4
#     
#     Fix this by having ftrace create a dummy stackframe for the function
#     being traced. With this, backtraces now capture the function being
#     traced:
#     
#     /sys/kernel/debug/tracing # cat stack_trace
#             Depth    Size   Location    (17 entries)
#             -----    ----   --------
#       0)     3888      32   _raw_spin_trylock+0x8/0x70
#       1)     3856     576   get_page_from_freelist+0x26c/0x1ad0
#       2)     3280      64   __alloc_pages+0x290/0x1280
#       3)     3216     336   __folio_alloc+0x34/0x90
#       4)     2880     176   vma_alloc_folio+0xd8/0x540
#       5)     2704     416   __handle_mm_fault+0x700/0x1cc0
#       6)     2288      96   handle_mm_fault+0xf0/0x3f0
#       7)     2192      48   ___do_page_fault+0x3e4/0xbe0
#       8)     2144     192   do_page_fault+0x30/0xc0
#       9)     1952     608   data_access_common_virt+0x210/0x220
#      10)     1344      16   0xc0000000334bbb50
#      11)     1328     416   load_elf_binary+0x804/0x1b80
#      12)      912      64   bprm_execve+0x2d8/0x7e0
#      13)      848     176   do_execveat_common+0x1d0/0x2f0
#      14)      672     192   sys_execve+0x54/0x70
#      15)      480      64   system_call_exception+0x138/0x350
#      16)      416     416   system_call_common+0x160/0x2c4
#     
#     This results in two additional stores in the ftrace entry code, but
#     produces reliable backtraces.
#     
#     Fixes: 153086644fd1 ("powerpc/ftrace: Add support for -mprofile-kernel ftrace ABI")
#     Cc: stable@vger.kernel.org
#     Signed-off-by: Naveen N Rao <naveen@kernel.org>
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
#     Link: https://msgid.link/20230621051349.759567-1-naveen@kernel.org
# < /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 41a506ef71eb38d94fe133f565c87c3e06ccc072
# make -s -j 40 ARCH=powerpc O=/kisskb/build/powerpc-fixes_powernv_defconfig+NO_PERF_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  powernv_defconfig
# Added to kconfig CONFIG_PERF_EVENTS=n
# < make -s -j 40 ARCH=powerpc O=/kisskb/build/powerpc-fixes_powernv_defconfig+NO_PERF_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  help
# make -s -j 40 ARCH=powerpc O=/kisskb/build/powerpc-fixes_powernv_defconfig+NO_PERF_powerpc-gcc5 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-5.5.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  olddefconfig
# make -s -j 40 ARCH=powerpc O=/kisskb/build/powerpc-fixes_powernv_defconfig+NO_PERF_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_powernv_defconfig+NO_PERF_powerpc-gcc5
# Build took: 0:01:37.132915