cmd/5l, cmd/6l, cmd/8l, cmd/gc, runtime: generate and use bitmaps of argument pointer locations

With this change the compiler emits a bitmap for each function
covering its stack frame arguments area.  If an argument word
is known to contain a pointer, a bit is set.  The garbage
collector reads this information when scanning the stack by
frames and uses it to ignores locations known to not contain a
pointer.

R=golang-dev, bradfitz, daniel.morsing, dvyukov, khr, khr, iant, cshapiro
CC=golang-dev
https://codereview.appspot.com/9223046

4 files changed, 39 insertions, 0 deletions

diff --git a/src/cmd/6l/6.out.h b/src/cmd/6l/6.out.h
index 237a802cd..e0aeafa94 100644
--- a/src/cmd/6l/6.out.h
+++ b/src/cmd/6l/6.out.h
@@ -763,6 +763,8 @@ enum	as
 	AUSEFIELD,
 	ALOCALS,
 	ATYPE,
+	ANPTRS,
+	APTRS,
 
 	ALAST
 };
diff --git a/src/cmd/6l/l.h b/src/cmd/6l/l.h
index 4d481c69d..d40cc741b 100644
--- a/src/cmd/6l/l.h
+++ b/src/cmd/6l/l.h
@@ -161,6 +161,8 @@ struct	Sym
 	int32	elfsym;
 	int32	locals;	// size of stack frame locals area
 	int32	args;	// size of stack frame incoming arguments area
+	int32	nptrs;	// number of bits in the pointer map
+	uint32*	ptrs;	// pointer map data
 	Sym*	hash;	// in hash table
 	Sym*	allsym;	// in all symbol list
 	Sym*	next;	// in text or data list
diff --git a/src/cmd/6l/obj.c b/src/cmd/6l/obj.c
index e98f91eeb..b4e77388d 100644
--- a/src/cmd/6l/obj.c
+++ b/src/cmd/6l/obj.c
@@ -616,6 +616,38 @@ loop:
 		pc++;
 		goto loop;
 
+	case ANPTRS:
+		if(skip)
+			goto casdef;
+		if(cursym->nptrs != -1) {
+			diag("ldobj1: multiple pointer maps defined for %s", cursym->name);
+			errorexit();
+		}
+		if(p->to.offset > cursym->args/PtrSize) {
+			diag("ldobj1: pointer map definition for %s exceeds its argument size", cursym->name);
+			errorexit();
+		}
+		cursym->nptrs = p->to.offset;
+		if(cursym->nptrs != 0)
+			cursym->ptrs = mal((rnd(cursym->nptrs, 32) / 32) * sizeof(*cursym->ptrs));
+		pc++;
+		goto loop;
+
+	case APTRS:
+		if(skip)
+			goto casdef;
+		if(cursym->nptrs == -1 || cursym->ptrs == NULL) {
+			diag("ldobj1: pointer map data provided for %s without a definition", cursym->name);
+			errorexit();
+		}
+		if(p->from.offset*32 >= rnd(cursym->nptrs, 32)) {
+			diag("ldobj1: excessive pointer map data provided for %s", cursym->name);
+			errorexit();
+		}
+		cursym->ptrs[p->from.offset] = p->to.offset;
+		pc++;
+		goto loop;
+
 	case ATEXT:
 		s = p->from.sym;
 		if(s->text != nil) {
@@ -660,6 +692,7 @@ loop:
 		s->type = STEXT;
 		s->value = pc;
 		s->args = p->to.offset >> 32;
+		s->nptrs = -1;
 		lastp = p;
 		p->pc = pc++;
 		goto loop;
diff --git a/src/cmd/6l/optab.c b/src/cmd/6l/optab.c
index b0d5ca788..34c8a0c12 100644
--- a/src/cmd/6l/optab.c
+++ b/src/cmd/6l/optab.c
@@ -1337,6 +1337,8 @@ Optab optab[] =
 	{ AUSEFIELD,	ynop,	Px, 0,0 },
 	{ ALOCALS },
 	{ ATYPE },
+	{ ANPTRS },
+	{ APTRS },
 
 	{ AEND },
 	0