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Naveen N Rao b8ea2a4691 powerpc/ftrace: Create a dummy stackframe to fix stack unwind 
commit 41a506ef71 upstream.

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: 153086644f ("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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2023-08-11 12:08:21 +02:00
..
boot powerpc: dts: turris1x.dts: Fix PCIe MEM size for pci2 node 2023-07-19 16:22:04 +02:00
configs - Yu Zhao's Multi-Gen LRU patches are here. They've been under test in 2022-10-10 17:53:04 -07:00
crypto treewide: use get_random_bytes() when possible 2022-10-11 17:42:58 -06:00
include word-at-a-time: use the same return type for has_zero regardless of endianness 2023-08-11 12:08:11 +02:00
kernel powerpc/ftrace: Create a dummy stackframe to fix stack unwind 2023-08-11 12:08:21 +02:00
kexec powerpc/64/kdump: Limit kdump base to 512MB 2022-09-28 19:22:09 +10:00
kvm KVM: PPC: BookS PR-KVM and BookE do not support context tracking 2022-10-18 22:46:19 +11:00
lib powerpc: Fix reschedule bug in KUAP-unlocked user copy 2022-10-18 22:46:19 +11:00
math-emu powerpc/math-emu: Inhibit W=1 warnings 2022-09-08 11:11:18 +10:00
mm powerpc/64s: Fix native_hpte_remove() to be irq-safe 2023-07-23 13:49:33 +02:00
net powerpc/bpf/32: Only set a stack frame when necessary 2023-03-17 08:50:30 +01:00
perf powerpc/perf: Properly detect mpc7450 family 2023-05-11 23:03:31 +09:00
platforms powerpc/pseries/vas: Hold mmap_mutex after mmap lock during window close 2023-08-03 10:23:48 +02:00
purgatory powerpc/purgatory: remove PGO flags 2023-06-21 16:00:55 +02:00
sysdev powerpc/sysdev/tsi108: fix resource printk format warnings 2023-05-11 23:03:31 +09:00
tools powerpc/64: Add UADDR64 relocation support 2022-03-09 21:47:53 +11:00
xmon powerpc/xmon: Use KSYM_NAME_LEN in array size 2023-06-09 10:34:26 +02:00
Kbuild
Kconfig powerpc/mm: Convert to using lock_mm_and_find_vma() 2023-07-01 13:16:24 +02:00
Kconfig.debug powerpc: allow PPC_EARLY_DEBUG_CPM only when SERIAL_CPM=y 2023-07-19 16:22:04 +02:00
Makefile powerpc: Fail build if using recordmcount with binutils v2.37 2023-07-23 13:49:32 +02:00
Makefile.postlink