gdb: introduce FRAME_SCOPED_DEBUG_ENTER_EXIT

gdb: introduce FRAME_SCOPED_DEBUG_ENTER_EXIT

Introduce FRAME_SCOPED_DEBUG_ENTER_EXIT and use it to print enter/exit
messages in important frame-related functions.  I think this helps
understand which lower-level operations are done as part of which
higher-level operation.  And it helps visually skip over a higher-level
operation you are not interested in.

Here's an example, combined with some py-unwind messages:

    [frame] frame_unwind_find_by_frame: enter
      [frame] frame_unwind_find_by_frame: this_frame=0
      [frame] frame_unwind_try_unwinder: trying unwinder "dummy"
      [frame] frame_unwind_try_unwinder: no
      [frame] frame_unwind_try_unwinder: trying unwinder "dwarf2 tailcall"
      [frame] frame_unwind_try_unwinder: no
      [frame] frame_unwind_try_unwinder: trying unwinder "inline"
      [frame] frame_unwind_try_unwinder: no
      [frame] frame_unwind_try_unwinder: trying unwinder "jit"
      [frame] frame_unwind_try_unwinder: no
      [frame] frame_unwind_try_unwinder: trying unwinder "python"
      [py-unwind] pyuw_sniffer: enter
        [frame] frame_unwind_register_value: enter
          [frame] frame_unwind_register_value: frame=-1, regnum=7(rsp)
          [frame] frame_unwind_register_value:   -> register=7 bytes=[40ddffffff7f0000]
        [frame] frame_unwind_register_value: exit
        [py-unwind] pyuw_sniffer: frame=0, sp=0x7fffffffdd40, pc=0x5555555551ec
        [frame] frame_id_p: l={stack=<sentinel>,!code,special=0x0000000000000000} -> 1
        [frame] frame_id_p: l={stack=<sentinel>,!code,special=0x0000000000000000} -> 1
        [frame] frame_id_eq: l={stack=<sentinel>,!code,special=0x0000000000000000}, r={stack=<sentinel>,!code,special=0x0000000000000000} -> 1
        [frame] frame_unwind_register_value: enter
          [frame] frame_unwind_register_value: frame=-1, regnum=6(rbp)
          [frame] frame_unwind_register_value:   -> register=6 bytes=[50ddffffff7f0000]
        [frame] frame_unwind_register_value: exit
        [frame] frame_id_p: l={stack=<sentinel>,!code,special=0x0000000000000000} -> 1
        [frame] frame_id_eq: l={stack=<sentinel>,!code,special=0x0000000000000000}, r={stack=<sentinel>,!code,special=0x0000000000000000} -> 1
        [frame] get_prev_frame: enter
          [frame] get_prev_frame_always_1: enter
            [frame] get_prev_frame_always_1: this_frame=-1
            [frame] get_prev_frame_always_1:   -> {level=0,type=NORMAL_FRAME,unwind=0x5588ee3d17c0,pc=0x5555555551ec,id=<not computed>,func=<unknown>} // cached
          [frame] get_prev_frame_always_1: exit
        [frame] get_prev_frame: exit
        [frame] value_fetch_lazy_register: (frame=0, regnum=6(rbp), ...) -> register=6 bytes=[50ddffffff7f0000]
        [frame] frame_id_p: l={stack=<sentinel>,!code,special=0x0000000000000000} -> 1
        [frame] frame_id_p: l={stack=<sentinel>,!code,special=0x0000000000000000} -> 1
        [frame] frame_id_eq: l={stack=<sentinel>,!code,special=0x0000000000000000}, r={stack=<sentinel>,!code,special=0x0000000000000000} -> 1
        [frame] frame_unwind_register_value: enter
          [frame] frame_unwind_register_value: frame=-1, regnum=7(rsp)
          [frame] frame_unwind_register_value:   -> register=7 bytes=[40ddffffff7f0000]
        [frame] frame_unwind_register_value: exit
        [frame] frame_id_p: l={stack=<sentinel>,!code,special=0x0000000000000000} -> 1
        [frame] frame_id_eq: l={stack=<sentinel>,!code,special=0x0000000000000000}, r={stack=<sentinel>,!code,special=0x0000000000000000} -> 1
        [frame] get_prev_frame: enter
          [frame] get_prev_frame_always_1: enter
            [frame] get_prev_frame_always_1: this_frame=-1
            [frame] get_prev_frame_always_1:   -> {level=0,type=NORMAL_FRAME,unwind=0x5588ee3d1824,pc=0x5555555551ec,id=<not computed>,func=<unknown>} // cached
          [frame] get_prev_frame_always_1: exit
        [frame] get_prev_frame: exit
        [frame] value_fetch_lazy_register: (frame=0, regnum=7(rsp), ...) -> register=7 bytes=[40ddffffff7f0000]
        [frame] frame_id_p: l={stack=<sentinel>,!code,special=0x0000000000000000} -> 1
        [frame] frame_id_p: l={stack=<sentinel>,!code,special=0x0000000000000000} -> 1
        [frame] frame_id_eq: l={stack=<sentinel>,!code,special=0x0000000000000000}, r={stack=<sentinel>,!code,special=0x0000000000000000} -> 1
        [frame] frame_unwind_register_value: enter
          [frame] frame_unwind_register_value: frame=-1, regnum=16(rip)
          [frame] frame_unwind_register_value:   -> register=16 bytes=[ec51555555550000]
        [frame] frame_unwind_register_value: exit
        [frame] frame_id_p: l={stack=<sentinel>,!code,special=0x0000000000000000} -> 1
        [frame] frame_id_eq: l={stack=<sentinel>,!code,special=0x0000000000000000}, r={stack=<sentinel>,!code,special=0x0000000000000000} -> 1
        [frame] get_prev_frame: enter
          [frame] get_prev_frame_always_1: enter
            [frame] get_prev_frame_always_1: this_frame=-1
            [frame] get_prev_frame_always_1:   -> {level=0,type=NORMAL_FRAME,unwind=0x5588ee3d1888,pc=0x5555555551ec,id=<not computed>,func=<unknown>} // cached
          [frame] get_prev_frame_always_1: exit
        [frame] get_prev_frame: exit
        [frame] value_fetch_lazy_register: (frame=0, regnum=16(rip), ...) -> register=16 bytes=[ec51555555550000]
        [py-unwind] pyuw_sniffer: frame claimed by unwinder test unwinder
      [py-unwind] pyuw_sniffer: exit
      [frame] frame_unwind_try_unwinder: yes
    [frame] frame_unwind_find_by_frame: exit

gdb/ChangeLog:

	* frame.h (FRAME_SCOPED_DEBUG_ENTER_EXIT): New.
	* frame.c (compute_frame_id, get_prev_frame_always_1,
	get_prev_frame): Use FRAME_SCOPED_DEBUG_ENTER_EXIT.
	* frame-unwind.c (frame_unwind_find_by_frame): Likewise.
	(frame_unwind_register_value): Likewise.

Change-Id: I45b69b4ed962e70572bc55b8adfb211483c1eeed