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Naveen N Rao efe775c714 powerpc/ftrace: Create a dummy stackframe to fix stack unwind 
commit 41a506ef71eb38d94fe133f565c87c3e06ccc072 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>
2023-12-20 15:38:04 +01:00
..
alpha alpha: remove __init annotation from exported page_is_ram() 2023-08-16 18:13:01 +02:00
arc ARC: define ASM_NL and __ALIGN(_STR) outside #ifdef __ASSEMBLY__ guard 2023-08-11 11:45:11 +02:00
arm ARM: dts: imx7: Declare timers compatible with fsl,imx6dl-gpt 2023-12-13 17:42:18 +01:00
arm64 arm64: mm: Always make sw-dirty PTEs hw-dirty in pte_modify 2023-12-20 15:38:03 +01:00
c6x
h8300 h8300: Fix build errors from do_exit() to make_task_dead() transition 2023-02-06 07:49:45 +01:00
hexagon hexagon: Fix function name in die() 2023-02-06 07:49:45 +01:00
ia64 treewide: Remove uninitialized_var() usage 2023-08-11 11:45:01 +02:00
m68k m68k: Fix invalid .section syntax 2023-09-23 10:47:57 +02:00
microblaze exit: Add and use make_task_dead. 2023-02-06 07:49:45 +01:00
mips MIPS: KVM: Fix a build warning about variable set but not used 2023-12-08 08:43:23 +01:00
nds32 exit: Add and use make_task_dead. 2023-02-06 07:49:45 +01:00
nios2 nios2: dts: Fix tse_mac "max-frame-size" property 2023-06-21 15:39:57 +02:00
openrisc openrisc: Properly store r31 to pt_regs on unhandled exceptions 2023-05-17 11:13:19 +02:00
parisc parisc/pgtable: Do not drop upper 5 address bits of physical address 2023-11-28 16:46:35 +00:00
powerpc powerpc/ftrace: Create a dummy stackframe to fix stack unwind 2023-12-20 15:38:04 +01:00
riscv riscv: Bump COMMAND_LINE_SIZE value to 1024 2023-04-05 11:15:36 +02:00
s390 KVM: s390/mm: Properly reset no-dat 2023-12-13 17:42:20 +01:00
sh sh: bios: Revive earlyprintk support 2023-11-20 10:29:19 +01:00
sparc sparc: fix up arch_cpu_finalize_init() build breakage. 2023-08-16 18:12:59 +02:00
um um: Fix hostaudio build errors 2023-09-23 10:48:09 +02:00
unicore32
x86 x86/CPU/AMD: Check vendor in the AMD microcode callback 2023-12-13 17:42:20 +01:00
xtensa xtensa: ISS: fix call to split_if_spec 2023-08-11 11:45:23 +02:00
.gitignore
Kconfig init: Provide arch_cpu_finalize_init() 2023-08-08 19:49:17 +02:00