[68]l and runtime: GDB support for interfaces and goroutines.

R=rsc
CC=golang-dev
https://golang.org/cl/3477041

Author: Luuk van Dijk

src/cmd/ld/dwarf.c

@@ -11,6 +11,7 @@
 //     ptype struct '[]uint8' and qualifiers need to be quoted away
 //   - lexical scoping is lost, so gdb gets confused as to which 'main.i' you mean.
 //   - file:line info for variables
+//   - make strings a typedef so prettyprinters can see the underlying string type
 //
 #include	"l.h"
 #include	"lib.h"
@@ -280,8 +281,9 @@ static struct DWAbbrev {
 
 	/* IFACETYPE */
 	{
-		DW_TAG_interface_type, DW_CHILDREN_no,
+		DW_TAG_typedef, DW_CHILDREN_yes,
 		DW_AT_name,	 DW_FORM_string,
+		DW_AT_type,	DW_FORM_ref_addr,
 		0, 0
 	},
 
@@ -957,6 +959,14 @@ decodetype_structfieldoffs(Sym *s, int i)
 	return decode_inuxi(s->p + 10*PtrSize + 0x10 + i*5*PtrSize, 4);	 // 0x38  / 0x60
 }
 
+// InterfaceTYpe.methods.len
+static vlong
+decodetype_ifacemethodcount(Sym *s)
+{
+	return decode_inuxi(s->p + 6*PtrSize + 8, 4);
+}
+
+
 // Fake attributes for slices, maps and channel
 enum {
 	DW_AT_internal_elem_type = 250,	 // channels and slices
@@ -1095,6 +1105,12 @@ defgotype(Sym *gotype)
 	case KindInterface:
 		die = newdie(&dwtypes, DW_ABRV_IFACETYPE, name);
 		newattr(die, DW_AT_byte_size, DW_CLS_CONSTANT, bytesize, 0);
+		nfields = decodetype_ifacemethodcount(gotype);
+		if (nfields == 0)
+			s = lookup("type.runtime.eface", 0);
+		else
+			s = lookup("type.runtime.iface", 0);
+		newrefattr(die, DW_AT_type, defgotype(s));
 		break;
 
 	case KindMap:
@@ -1425,8 +1441,13 @@ defdwsymb(Sym* sym, char *s, int t, vlong v, vlong size, int ver, Sym *gotype)
 		return;
 	if (strncmp(s, "string.", 7) == 0)
 		return;
-	if (strncmp(s, "type.", 5) == 0)
+	if (strncmp(s, "type._.", 7) == 0)
+		return;
+
+	if (strncmp(s, "type.", 5) == 0) {
+		defgotype(sym);
 		return;
+	}
 
 	dv = nil;
 
@@ -2291,6 +2312,11 @@ dwarfemitdebugsections(void)
 	newattr(die, DW_AT_encoding,  DW_CLS_CONSTANT, DW_ATE_unsigned, 0);
 	newattr(die, DW_AT_byte_size, DW_CLS_CONSTANT, PtrSize, 0);
 
+	// Needed by the prettyprinter code for interface inspection.
+	defgotype(lookup("type.runtime.commonType",0));
+	defgotype(lookup("type.runtime.InterfaceType",0));
+	defgotype(lookup("type.runtime.itab",0));
+
 	genasmsym(defdwsymb);
 
 	writeabbrev();

src/pkg/runtime/runtime-gdb.py

@@ -9,10 +9,20 @@
 path to this file based on the path to the runtime package.
 """
 
+# Known issues:
+#    - pretty printing only works for the 'native' strings. E.g. 'type
+#      foo string' will make foo a plain struct in the eyes of gdb,
+#      circumventing the pretty print triggering.
+#    -
+
 import sys, re
 
 print >>sys.stderr, "Loading Go Runtime support."
 
+# allow to manually reload while developing
+goobjfile = gdb.current_objfile() or gdb.objfiles()[0]
+goobjfile.pretty_printers = []
+
 #
 #  Pretty Printers
 #
@@ -95,7 +105,7 @@ def traverse_hash(self, stab):
 class ChanTypePrinter:
 	"""Pretty print chan[T] types.
 
-	Map-typed go variables are really pointers. dereference them in gdb
+	Chan-typed go variables are really pointers. dereference them in gdb
 	to inspect their contents with this pretty printer.
 	"""
 
@@ -117,18 +127,109 @@ def children(self):
 			ptr = ptr['link']
 
 #
-#  Register all the *Printer classes
+#  Register all the *Printer classes above.
 #
 
 def makematcher(klass):
 	def matcher(val):
 		try:
-			if klass.pattern.match(str(val.type)): return klass(val)
-		except: pass
+			if klass.pattern.match(str(val.type)):
+				return klass(val)
+		except:
+			pass
 	return matcher
 
-gdb.current_objfile().pretty_printers.extend([makematcher(k) for k in vars().values() if hasattr(k, 'pattern')])
+goobjfile.pretty_printers.extend([makematcher(k) for k in vars().values() if hasattr(k, 'pattern')])
 
+#
+#  For reference, this is what we're trying to do:
+#  eface: p *(*(struct 'runtime.commonType'*)'main.e'->type_->data)->string
+#  iface: p *(*(struct 'runtime.commonType'*)'main.s'->tab->Type->data)->string
+#
+# interface types can't be recognized by their name, instead we check
+# if they have the expected fields.  Unfortunately the mapping of
+# fields to python attributes in gdb.py isn't complete: you can't test
+# for presence other than by trapping.
+
+
+def is_iface(val):
+	try:
+		return str(val['tab'].type) == "struct runtime.itab *" \
+		      and str(val['data'].type) == "void *"
+	except:
+		pass
+
+def is_eface(val):
+	try:
+		return str(val['type_'].type) == "runtime.Type *" \
+		      and str(val['data'].type) == "void *"
+	except:
+		pass
+
+def lookup_type(name):
+	try:
+		return gdb.lookup_type(name)
+	except:
+		pass
+	try:
+		return gdb.lookup_type('struct ' + name)
+	except:
+		pass
+	try:
+		return gdb.lookup_type('struct ' + name[1:]).pointer()
+	except:
+		pass
+
+
+def iface_dtype(obj):
+	"Decode type of the data field of an eface or iface struct."
+
+	if is_iface(obj):
+		go_type_ptr = obj['tab']['Type']
+	elif is_eface(obj):
+		go_type_ptr = obj['type_']
+	else:
+		return
+
+	ct = gdb.lookup_type("struct runtime.commonType").pointer()
+	dynamic_go_type = go_type_ptr['data'].cast(ct).dereference()
+	dtype_name = dynamic_go_type['string'].dereference()['str'].string()
+	type_size = int(dynamic_go_type['size'])
+	uintptr_size = int(dynamic_go_type['size'].type.sizeof)  # size is itself an uintptr
+	dynamic_gdb_type = lookup_type(dtype_name)
+	if type_size > uintptr_size:
+		dynamic_gdb_type = dynamic_gdb_type.pointer()
+	return dynamic_gdb_type
+
+
+class IfacePrinter:
+	"""Pretty print interface values
+
+	Casts the data field to the appropriate dynamic type."""
+
+	def __init__(self, val):
+		self.val = val
+
+	def display_hint(self):
+		return 'string'
+
+	def to_string(self):
+		try:
+			dtype = iface_dtype(self.val)
+		except:
+			return "<bad dynamic type>"
+		try:
+			return self.val['data'].cast(dtype).dereference()
+		except:
+			pass
+		return self.val['data'].cast(dtype)
+
+
+def ifacematcher(val):
+	if is_iface(val) or is_eface(val):
+		return IfacePrinter(val)
+
+goobjfile.pretty_printers.append(ifacematcher)
 
 #
 #  Convenience Functions
@@ -137,35 +238,158 @@ def matcher(val):
 class GoLenFunc(gdb.Function):
 	"Length of strings, slices, maps or channels"
 
-        how = ((StringTypePrinter, 'len' ),
-               (SliceTypePrinter, 'len'),
-               (MapTypePrinter, 'count'),
-               (ChanTypePrinter, 'qcount'))
+	how = ((StringTypePrinter, 'len' ),
+	       (SliceTypePrinter, 'len'),
+	       (MapTypePrinter, 'count'),
+	       (ChanTypePrinter, 'qcount'))
 
 	def __init__(self):
 		super(GoLenFunc, self).__init__("len")
 
 	def invoke(self, obj):
 		typename = str(obj.type)
-                for klass, fld in self.how:
+		for klass, fld in self.how:
 			if klass.pattern.match(typename):
 				return obj[fld]
 
 class GoCapFunc(gdb.Function):
 	"Capacity of slices or channels"
 
-        how = ((SliceTypePrinter, 'cap'),
-               (ChanTypePrinter, 'dataqsiz'))
+	how = ((SliceTypePrinter, 'cap'),
+	       (ChanTypePrinter, 'dataqsiz'))
 
 	def __init__(self):
 		super(GoCapFunc, self).__init__("cap")
 
 	def invoke(self, obj):
 		typename = str(obj.type)
-                for klass, fld in self.how:
+		for klass, fld in self.how:
 			if klass.pattern.match(typename):
 				return obj[fld]
 
+class DTypeFunc(gdb.Function):
+	"""Cast Interface values to their dynamic type.
+
+	For non-interface types this behaves as the identity operation.
+	"""
+
+	def __init__(self):
+		super(DTypeFunc, self).__init__("dtype")
+
+	def invoke(self, obj):
+		try:
+			return obj['data'].cast(iface_dtype(obj))
+		except:
+			pass
+		return obj
+
+#
+#  Commands
+#
+
+sts = ( 'idle', 'runnable', 'running', 'syscall', 'waiting', 'moribund', 'dead', 'recovery')
+
+def linked_list(ptr, linkfield):
+	while ptr:
+		yield ptr
+		ptr = ptr[linkfield]
+
+
+class GoroutinesCmd(gdb.Command):
+	"List all goroutines."
+
+	def __init__(self):
+		super(GoroutinesCmd, self).__init__("info goroutines", gdb.COMMAND_STACK, gdb.COMPLETE_NONE)
+
+	def invoke(self, arg, from_tty):
+		# args = gdb.string_to_argv(arg)
+		vp = gdb.lookup_type('void').pointer()
+		for ptr in linked_list(gdb.parse_and_eval("'runtime.allg'"), 'alllink'):
+			if ptr['status'] == 6:	# 'gdead'
+				continue
+			m = ptr['m']
+			s = ' '
+			if m:
+				pc = m['sched']['pc'].cast(vp)
+				sp = m['sched']['sp'].cast(vp)
+				s = '*'
+			else:
+				pc = ptr['sched']['pc'].cast(vp)
+				sp = ptr['sched']['sp'].cast(vp)
+			blk = gdb.block_for_pc(long((pc)))
+			print s, ptr['goid'], "%8s" % sts[long((ptr['status']))], blk.function
+
+def find_goroutine(goid):
+	vp = gdb.lookup_type('void').pointer()
+	for ptr in linked_list(gdb.parse_and_eval("'runtime.allg'"), 'alllink'):
+		if ptr['status'] == 6:	# 'gdead'
+			continue
+		if ptr['goid'] == goid:
+			return [(ptr['m'] or ptr)['sched'][x].cast(vp) for x in 'pc', 'sp']
+	return None, None
+
+
+class GoroutineCmd(gdb.Command):
+	"""Execute gdb command in the context of goroutine <goid>.
+
+	Switch PC and SP to the ones in the goroutine's G structure,
+	execute an arbitrary gdb command, and restore PC and SP.
+
+	Usage: (gdb) goroutine <goid> <gdbcmd>
+
+	Note that it is ill-defined to modify state in the context of a goroutine.
+	Restrict yourself to inspecting values.
+	"""
+
+	def __init__(self):
+		super(GoroutineCmd, self).__init__("goroutine", gdb.COMMAND_STACK, gdb.COMPLETE_NONE)
+
+	def invoke(self, arg, from_tty):
+		goid, cmd = arg.split(None, 1)
+		pc, sp = find_goroutine(int(goid))
+		if not pc:
+			print "No such goroutine: ", goid
+			return
+		save_frame = gdb.selected_frame()
+		gdb.parse_and_eval('$save_pc = $pc')
+		gdb.parse_and_eval('$save_sp = $sp')
+		gdb.parse_and_eval('$pc = 0x%x' % long(pc))
+		gdb.parse_and_eval('$sp = 0x%x' % long(sp))
+		try:
+			gdb.execute(cmd)
+                finally:
+			gdb.parse_and_eval('$pc = $save_pc')
+                        gdb.parse_and_eval('$sp = $save_sp')
+                        save_frame.select()
+
+
+class GoIfaceCmd(gdb.Command):
+	"Print Static and dynamic interface types"
+
+	def __init__(self):
+		super(GoIfaceCmd, self).__init__("iface", gdb.COMMAND_DATA, gdb.COMPLETE_SYMBOL)
+
+	def invoke(self, arg, from_tty):
+		for obj in gdb.string_to_argv(arg):
+			try:
+				#TODO fix quoting for qualified variable names
+				obj = gdb.parse_and_eval("%s" % obj)
+			except Exception, e:
+				print "Can't parse ", obj, ": ", e
+				continue
+
+			dtype = iface_dtype(obj)
+			if not dtype:
+				print "Not an interface: ", obj.type
+				continue
+
+			print "%s: %s" % (obj.type, dtype)
+
+# TODO: print interface's methods and dynamic type's func pointers thereof.
+#rsc: "to find the number of entries in the itab's Fn field look at itab.inter->numMethods
+#i am sure i have the names wrong but look at the interface type and its method count"
+# so Itype will start with a commontype which has kind = interface
+
 #
 # Register all convience functions and CLI commands
 #