• AKASHI Takahiro's avatar
    arm64: ftrace: fix a stack tracer's output under function graph tracer · 20380bb3
    AKASHI Takahiro authored
    
    
    Function graph tracer modifies a return address (LR) in a stack frame
    to hook a function return. This will result in many useless entries
    (return_to_handler) showing up in
     a) a stack tracer's output
     b) perf call graph (with perf record -g)
     c) dump_backtrace (at panic et al.)
    
    For example, in case of a),
      $ echo function_graph > /sys/kernel/debug/tracing/current_tracer
      $ echo 1 > /proc/sys/kernel/stack_trace_enabled
      $ cat /sys/kernel/debug/tracing/stack_trace
            Depth    Size   Location    (54 entries)
            -----    ----   --------
      0)     4504      16   gic_raise_softirq+0x28/0x150
      1)     4488      80   smp_cross_call+0x38/0xb8
      2)     4408      48   return_to_handler+0x0/0x40
      3)     4360      32   return_to_handler+0x0/0x40
      ...
    
    In case of b),
      $ echo function_graph > /sys/kernel/debug/tracing/current_tracer
      $ perf record -e mem:XXX:x -ag -- sleep 10
      $ perf report
                      ...
                      |          |          |--0.22%-- 0x550f8
                      |          |          |          0x10888
                      |          |          |          el0_svc_naked
                      |          |          |          sys_openat
                      |          |          |          return_to_handler
                      |          |          |          return_to_handler
                      ...
    
    In case of c),
      $ echo function_graph > /sys/kernel/debug/tracing/current_tracer
      $ echo c > /proc/sysrq-trigger
      ...
      Call trace:
      [<ffffffc00044d3ac>] sysrq_handle_crash+0x24/0x30
      [<ffffffc000092250>] return_to_handler+0x0/0x40
      [<ffffffc000092250>] return_to_handler+0x0/0x40
      ...
    
    This patch replaces such entries with real addresses preserved in
    current->ret_stack[] at unwind_frame(). This way, we can cover all
    the cases.
    Reviewed-by: default avatarJungseok Lee <jungseoklee85@gmail.com>
    Signed-off-by: default avatarAKASHI Takahiro <takahiro.akashi@linaro.org>
    [will: fixed minor context changes conflicting with irq stack bits]
    Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
    20380bb3
traps.c 14 KB