DLPX-84435 Support printing local variables

[mmaybee]

Problem

Need to be able to find local variables and their values

Solution

This PR provodes 4 new commands: trace, frame, locals, and registers

sdb> help trace
SUMMARY
    trace [-h] [<task address>]
    
    Given a task_struct, trace the thread's execution state.
    
    positional arguments:
      <task address>  trace this task if no input
    
    optional arguments:
      -h, --help      show this help message and exit
    
ALIASES
    trace, bt

FIELDS
    frame# - frame number in backtrace (most recent first)
    addr - address of the frame
    function - function name in the frame (or symbol if no function)
    file - file name (if available) containing the function
    line - line number in the file

EXAMPLE
    sdb> trace 0xffff94614e796000
    TASK: 0xffff94614e796000 INTERRUPTIBLE PID: 268
    #0  0xffffffffa0c549e8 in context_switch() at core.c:5038:2 (inlined)
    #1  0xffffffffa0c549e8 in __schedule() at core.c:6384:8
    #2  0xffffffffa0c54fe9 in schedule() at core.c:6467:3
    #3  0xffffffffa0c595c2 in schedule_timeout() at timer.c:2116:2
    #4  0xffffffffc04836ae in __cv_timedwait_common() at spl-condvar.c:250:15
    #5  0xffffffffc0483829 in __cv_timedwait_idle() at spl-condvar.c:307:7
    #6  0xffffffffc0571554 in l2arc_feed_thread() at arc.c:9460:10
    #7  0xffffffffc048c8d1 in thread_generic_wrapper() at spl-thread.c:61:3
    #8  0xffffffffa00efb17 in kthread() at kthread.c:334:9
    #9  0xffffffffa0004c3f (ret_from_fork+0x1f/0x2d) at entry_64.S:287

sdb> help frame
SUMMARY
    frame [-h] [-v] [<frame>]
    
    Given a task_struct and frame, return requested stack frame
    
    positional arguments:
      <frame>        set local context to this frame number
    
    optional arguments:
      -h, --help     show this help message and exit
      -v, --verbose  print full file path for frame
    
ALIASES
    stackframe, frame, f

EXAMPLE
    sdb> frame 7
    #7  0xffffffffc048c8d1 in thread_generic_wrapper (arg=0xffff94614f3cc400) at spl-thread.c:61:3

sdb> help locals
SUMMARY
    locals [-h] [-v] [<variable> [<variable> ...]]
    
    Given a stack frame, return the local variables
    
    positional arguments:
      <variable>     variable to retrieve
    
    optional arguments:
      -h, --help     show this help message and exit
      -v, --verbose  dereference pointers
    
ALIASES
    locals, local

EXAMPLE
    sdb> frame 7 | locals
    arg = (void *)0xffff94614f3cc400
    tp = (thread_priv_t *)0xffff94614f3cc400
    func = (void (*)(void *))l2arc_feed_thread+0x0 = 0xffffffffc05714f0
    args = (void *)0x0

sdb> help registers
SUMMARY
    registers [-h] [-x] [<register> [<register> ...]]
    
    Given a stack frame, return the registers
    
    positional arguments:
      <register>  register to retrieve
    
    optional arguments:
      -h, --help  show this help message and exit
      -x, --hex   print registers in hexadecimal
    
ALIASES
    registers, register

EXAMPLE
    sdb> frame 7 | registers
    rbx = 18446744072641516784
    rbp = 18446653449961438984
    rsp = 18446653449961438960
    r12 = 18446625744394961920
    r13 = 0
    r14 = 18446653449906223704
    r15 = 18446625744394961920
    rip = 18446744072640579793

Testing Done

Verified commands on engine kernel