runtime: fix gdb support for channels.

R=rsc
CC=golang-dev
https://golang.org/cl/4418043

src/cmd/ld/dwarf.c

@@ -1376,20 +1376,18 @@ synthesizemaptypes(DWDie *die)
 static void
 synthesizechantypes(DWDie *die)
 {
-	DWDie *sudog, *waitq, *link, *hchan,
+	DWDie *sudog, *waitq, *hchan,
 		*dws, *dww, *dwh, *elemtype;
 	DWAttr *a;
-	int elemsize, linksize, sudogsize;
+	int elemsize, sudogsize;
 
 	sudog = defgotype(lookup_or_diag("type.runtime.sudog"));
 	waitq = defgotype(lookup_or_diag("type.runtime.waitq"));
-	link  = defgotype(lookup_or_diag("type.runtime.link"));
 	hchan = defgotype(lookup_or_diag("type.runtime.hchan"));
-	if (sudog == nil || waitq == nil || link == nil || hchan == nil)
+	if (sudog == nil || waitq == nil || hchan == nil)
 		return;
 
 	sudogsize = getattr(sudog, DW_AT_byte_size)->value;
-	linksize = getattr(link, DW_AT_byte_size)->value;
 
 	for (; die != nil; die = die->link) {
 		if (die->abbrev != DW_ABRV_CHANTYPE)
@@ -1422,7 +1420,7 @@ synthesizechantypes(DWDie *die)
 		copychildren(dwh, hchan);
 		substitutetype(dwh, "recvq", dww);
 		substitutetype(dwh, "sendq", dww);
-		substitutetype(dwh, "free", dws);
+		substitutetype(dwh, "free", defptrto(dws));
 		newattr(dwh, DW_AT_byte_size, DW_CLS_CONSTANT,
 			getattr(hchan, DW_AT_byte_size)->value, NULL);
 

src/pkg/runtime/chan.c

@@ -9,7 +9,6 @@
 
 static	int32	debug	= 0;
 
-typedef	struct	Link	Link;
 typedef	struct	WaitQ	WaitQ;
 typedef	struct	SudoG	SudoG;
 typedef	struct	Select	Select;
@@ -51,12 +50,6 @@ struct	Hchan
 // chanbuf(c, i) is pointer to the i'th slot in the buffer.
 #define chanbuf(c, i) ((byte*)((c)+1)+(uintptr)(c)->elemsize*(i))
 
-struct	Link
-{
-	Link*	link;			// asynch queue circular linked list
-	byte	elem[8];		// asynch queue data element (+ more)
-};
-
 enum
 {
 	// Scase.kind

src/pkg/runtime/runtime-gdb.py

@@ -122,10 +122,13 @@ class ChanTypePrinter:
 		return str(self.val.type)
 
 	def children(self):
-		ptr = self.val['recvdataq']
-		for idx in range(self.val["qcount"]):
-			yield ('[%d]' % idx, ptr['elem'])
-			ptr = ptr['link']
+		# see chan.c chanbuf()
+		et = [x.type for x in self.val['free'].type.target().fields() if x.name == 'elem'][0]
+                ptr = (self.val.address + 1).cast(et.pointer())
+                for i in range(self.val["qcount"]):
+			j = (self.val["recvx"] + i) % self.val["dataqsiz"]
+			yield ('[%d]' % i, (ptr + j).dereference())
+
 
 #
 #  Register all the *Printer classes above.