scripts/gdb: add 'lx-stack_depot_lookup' command.

This command allows users to quickly retrieve a stacktrace using a handle
obtained from a memory coredump.

Example output:
(gdb) lx-stack_depot_lookup 0x00c80300
   0xffff8000807965b4 <kmem_cache_alloc_noprof+660>:    mov     x20, x0
   0xffff800081a077d8 <kmem_cache_oob_alloc+76>:        mov     x1, x0
   0xffff800081a079a0 <test_version_show+100>:  cbnz    w0, 0xffff800081a07968 <test_version_show+44>
   0xffff800082f4a3fc <kobj_attr_show+60>:      ldr     x19, [sp, torvalds#16]
   0xffff800080a0fb34 <sysfs_kf_seq_show+460>:  ldp     x3, x4, [sp, torvalds#96]
   0xffff800080a0a550 <kernfs_seq_show+296>:    ldp     x19, x20, [sp, torvalds#16]
   0xffff8000808e7b40 <seq_read_iter+836>:      mov     w5, w0
   0xffff800080a0b8ac <kernfs_fop_read_iter+804>:       mov     x23, x0
   0xffff800080914a48 <copy_splice_read+972>:   mov     x6, x0
   0xffff8000809151c4 <do_splice_read+348>:     ldr     x21, [sp, torvalds#32]

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Kuan-Ying Lee <[email protected]>
Cc: Jan Kiszka <[email protected]>
Cc: Kieran Bingham <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

scripts/gdb/linux/stackdepot.py

@@ -13,6 +13,13 @@
     stack_record_type = utils.CachedType('struct stack_record')
     DEPOT_STACK_ALIGN = 4
 
+def help():
+    t = """Usage: lx-stack_depot_lookup [Hex handle value]
+    Example:
+        lx-stack_depot_lookup 0x00c80300\n"""
+    gdb.write("Unrecognized command\n")
+    raise gdb.GdbError(t)
+
 def stack_depot_fetch(handle):
     global DEPOT_STACK_ALIGN
     global stack_record_type
@@ -57,3 +64,23 @@ def stack_depot_print(handle):
                 gdb.execute("x /i 0x%x" % (int(entries[i])))
             except Exception as e:
                 gdb.write("%s\n" % e)
+
+class StackDepotLookup(gdb.Command):
+    """Search backtrace by handle"""
+
+    def __init__(self):
+        if constants.LX_CONFIG_STACKDEPOT:
+            super(StackDepotLookup, self).__init__("lx-stack_depot_lookup", gdb.COMMAND_SUPPORT)
+
+    def invoke(self, args, from_tty):
+        if not constants.LX_CONFIG_STACKDEPOT:
+            raise gdb.GdbError('CONFIG_STACKDEPOT is not set')
+
+        argv = gdb.string_to_argv(args)
+        if len(argv) == 1:
+            handle = int(argv[0], 16)
+            stack_depot_print(gdb.Value(handle).cast(utils.get_uint_type()))
+        else:
+            help()
+
+StackDepotLookup()