dbg: introduce lj-gco command

Our GDB extension already has dumpers for TValues. But sometimes it
may be useful to dump GC objects (GCobj) without stack context. This
patch adds additional wrappers around dumpers for GC objects to get the
corresponding GC object from a TValue. Also, the lj-gco command is
introduced. It allows dumping GC objects without stack context. The
output format is the same as for the lj-tv command.

Part of tarantool/tarantool#4808

Reviewed-by: Evgeniy Temirgaleev <e.temirgaleev@tarantool.org>
Reviewed-by: Sergey Bronnikov <sergeyb@tarantool.org>
Signed-off-by: Sergey Kaplun <skaplun@tarantool.org>
(cherry picked from commit 7b919c0)

Author: Buristan

src/luajit_dbg.py

@@ -882,44 +882,29 @@ def lightudV(tv):
 
 # Dumpers.
 
+# GCobj dumpers.
 
-def dump_lj_tnil(tv):
-    return 'nil'
-
-
-def dump_lj_tfalse(tv):
-    return 'false'
-
-
-def dump_lj_ttrue(tv):
-    return 'true'
-
-
-def dump_lj_tlightud(tv):
-    return 'light userdata @ {}'.format(strx64(lightudV(tv)))
-
-
-def dump_lj_tstr(tv):
+def dump_lj_gco_str(gcobj):
     return 'string {body} @ {address}'.format(
-        body=strdata(gcval(tv['gcr'])),
-        address=strx64(gcval(tv['gcr']))
+        body=strdata(gcobj),
+        address=strx64(gcobj)
     )
 
 
-def dump_lj_tupval(tv):
-    return 'upvalue @ {}'.format(strx64(gcval(tv['gcr'])))
+def dump_lj_gco_upval(gcobj):
+    return 'upvalue @ {}'.format(strx64(gcobj))
 
 
-def dump_lj_tthread(tv):
-    return 'thread @ {}'.format(strx64(gcval(tv['gcr'])))
+def dump_lj_gco_thread(gcobj):
+    return 'thread @ {}'.format(strx64(gcobj))
 
 
-def dump_lj_tproto(tv):
-    return 'proto @ {}'.format(strx64(gcval(tv['gcr'])))
+def dump_lj_gco_proto(gcobj):
+    return 'proto @ {}'.format(strx64(gcobj))
 
 
-def dump_lj_tfunc(tv):
-    func = dbg.cast('struct GCfuncC *', gcval(tv['gcr']))
+def dump_lj_gco_func(gcobj):
+    func = dbg.cast('struct GCfuncC *', gcobj)
     ffid = func['ffid']
 
     if ffid == 0:
@@ -936,62 +921,115 @@ def dump_lj_tfunc(tv):
         return 'fast function #{}'.format(int(ffid))
 
 
-def dump_lj_ttrace(tv):
-    trace = dbg.cast('struct GCtrace *', gcval(tv['gcr']))
+def dump_lj_gco_trace(gcobj):
+    trace = dbg.cast('struct GCtrace *', gcobj)
     return 'trace {traceno} @ {addr}'.format(
         traceno=strx64(trace['traceno']),
         addr=strx64(trace)
     )
 
 
-def dump_lj_tcdata(tv):
-    return 'cdata @ {}'.format(strx64(gcval(tv['gcr'])))
+def dump_lj_gco_cdata(gcobj):
+    return 'cdata @ {}'.format(strx64(gcobj))
 
 
-def dump_lj_ttab(tv):
-    table = dbg.cast('GCtab *', gcval(tv['gcr']))
+def dump_lj_gco_tab(gcobj):
+    table = dbg.cast('GCtab *', gcobj)
     return 'table @ {gcr} (asize: {asize}, hmask: {hmask})'.format(
         gcr=strx64(table),
         asize=table['asize'],
         hmask=strx64(table['hmask']),
     )
 
 
-def dump_lj_tudata(tv):
-    return 'userdata @ {}'.format(strx64(gcval(tv['gcr'])))
+def dump_lj_gco_udata(gcobj):
+    return 'userdata @ {}'.format(strx64(gcobj))
+
+
+def dump_lj_gco_invalid(gcobj):
+    return 'not valid type @ {}'.format(strx64(gcobj))
+
+
+# TValue dumpers
+
+def dump_lj_tv_nil(tv):
+    return 'nil'
+
+
+def dump_lj_tv_false(tv):
+    return 'false'
+
+
+def dump_lj_tv_true(tv):
+    return 'true'
+
+
+def dump_lj_tv_lightud(tv):
+    return 'light userdata @ {}'.format(strx64(lightudV(tv)))
+
+
+# Generate wrappers for TValues containing GCobj.
+gco_fn_dumpers = [
+    fn for fn in globals().keys() if fn.startswith('dump_lj_gco')
+]
+for fn_name in gco_fn_dumpers:
+    wrapped_fn_name = fn_name.replace('gco', 'tv')
+    # Lambda takes `fn_name` as a reference, so the additional
+    # lambda is needed to fixate the correct wrapper.
+    globals()[wrapped_fn_name] = (lambda f: (
+        lambda tv: globals()[f](gcval(tv['gcr']))
+    ))(fn_name)
 
 
-def dump_lj_tnumx(tv):
+def dump_lj_tv_numx(tv):
     if tvisint(tv):
         return 'integer {}'.format(dbg.cast('int32_t', tv['i']))
     else:
         return 'number {}'.format(dbg.cast('double', tv['n']))
 
 
-def dump_lj_invalid(tv):
-    return 'not valid type @ {}'.format(strx64(gcval(tv['gcr'])))
-
-
-dumpers = {
-    'LJ_TNIL':     dump_lj_tnil,
-    'LJ_TFALSE':   dump_lj_tfalse,
-    'LJ_TTRUE':    dump_lj_ttrue,
-    'LJ_TLIGHTUD': dump_lj_tlightud,
-    'LJ_TSTR':     dump_lj_tstr,
-    'LJ_TUPVAL':   dump_lj_tupval,
-    'LJ_TTHREAD':  dump_lj_tthread,
-    'LJ_TPROTO':   dump_lj_tproto,
-    'LJ_TFUNC':    dump_lj_tfunc,
-    'LJ_TTRACE':   dump_lj_ttrace,
-    'LJ_TCDATA':   dump_lj_tcdata,
-    'LJ_TTAB':     dump_lj_ttab,
-    'LJ_TUDATA':   dump_lj_tudata,
-    'LJ_TNUMX':    dump_lj_tnumx,
+gco_dumpers = {
+    'LJ_TSTR':     dump_lj_gco_str,
+    'LJ_TUPVAL':   dump_lj_gco_upval,
+    'LJ_TTHREAD':  dump_lj_gco_thread,
+    'LJ_TPROTO':   dump_lj_gco_proto,
+    'LJ_TFUNC':    dump_lj_gco_func,
+    'LJ_TTRACE':   dump_lj_gco_trace,
+    'LJ_TCDATA':   dump_lj_gco_cdata,
+    'LJ_TTAB':     dump_lj_gco_tab,
+    'LJ_TUDATA':   dump_lj_gco_udata,
 }
 
 
+tv_dumpers = {
+    'LJ_TNIL':     dump_lj_tv_nil,
+    'LJ_TFALSE':   dump_lj_tv_false,
+    'LJ_TTRUE':    dump_lj_tv_true,
+    'LJ_TLIGHTUD': dump_lj_tv_lightud,
+    'LJ_TSTR':     dump_lj_tv_str,  # noqa: F821 # Generated.
+    'LJ_TUPVAL':   dump_lj_tv_upval,  # noqa: F821 # Generated.
+    'LJ_TTHREAD':  dump_lj_tv_thread,  # noqa: F821 # Generated.
+    'LJ_TPROTO':   dump_lj_tv_proto,  # noqa: F821 # Generated.
+    'LJ_TFUNC':    dump_lj_tv_func,  # noqa: F821 # Generated.
+    'LJ_TTRACE':   dump_lj_tv_trace,  # noqa: F821 # Generated.
+    'LJ_TCDATA':   dump_lj_tv_cdata,  # noqa: F821 # Generated.
+    'LJ_TTAB':     dump_lj_tv_tab,  # noqa: F821 # Generated.
+    'LJ_TUDATA':   dump_lj_tv_udata,  # noqa: F821 # Generated.
+    'LJ_TNUMX':    dump_lj_tv_numx,
+}
+
+
+def dump_gcobj(gcobj):
+    return gco_dumpers.get(
+        typenames(i2notu32(gcobj['gch']['gct'])), dump_lj_gco_invalid
+    )(gcobj)
+
+
 def dump_tvalue(tvalue):
-    return dumpers.get(typenames(itypemap(tvalue)), dump_lj_invalid)(tvalue)
+    return tv_dumpers.get(
+        typenames(itypemap(tvalue)),
+        dump_lj_tv_invalid  # noqa: F821 # Generated.
+    )(tvalue)
 
 
 def dump_framelink_slot_address(fr):
@@ -1011,7 +1049,7 @@ def dump_framelink(L, fr):
             p='P' if frame_typep(fr) & FRAME_P else ''
         ),
         d=dbg.cast('TValue *', fr) - dbg.cast('TValue *', frame_prev(fr)),
-        f=dump_lj_tfunc(fr - LJ_FR2),
+        f=dump_lj_tv_func(fr - LJ_FR2),  # noqa: F821 # Generated.
     )
 
 
@@ -1142,6 +1180,35 @@ def execute(self, arg):
         ))
 
 
+class LJDumpGCobj(dbg.LJBase):
+    '''
+lj-gco <GCobj *>
+
+The command receives a pointer to <GCobj> (GCobj address) and dumps
+the type and some info related to it.
+
+* LJ_TSTR: string <string payload> @ <gcr>
+* LJ_TUPVAL: upvalue @ <gcr>
+* LJ_TTHREAD: thread @ <gcr>
+* LJ_TPROTO: proto @ <gcr>
+* LJ_TFUNC: <LFUNC|CFUNC|FFUNC>
+  <LFUNC>: Lua function @ <gcr>, <nupvals> upvalues, <chunk:line>
+  <CFUNC>: C function <mcode address>
+  <FFUNC>: fast function #<ffid>
+* LJ_TTRACE: trace <traceno> @ <gcr>
+* LJ_TCDATA: cdata @ <gcr>
+* LJ_TTAB: table @ <gcr> (asize: <asize>, hmask: <hmask>)
+* LJ_TUDATA: userdata @ <gcr>
+
+Whether the type of the given address differs from the listed above, then
+error message occurs.
+    '''
+
+    def execute(self, arg):
+        gcobj = dbg.cast('GCobj *', dbg.eval(arg))
+        dbg.write('{}\n'.format(dump_gcobj(gcobj)))
+
+
 class LJDumpStack(dbg.LJBase):
     '''
 lj-stack [<lua_State *>]
@@ -1303,6 +1370,7 @@ def load(event=None):
     dbg.initialize_extension({
         'lj-arch':  LJDumpArch,
         'lj-gc':    LJGC,
+        'lj-gco':   LJDumpGCobj,
         'lj-stack': LJDumpStack,
         'lj-state': LJState,
         'lj-str':   LJDumpString,