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://golang.org/cl/9223046

1 files changed, 33 insertions, 0 deletions

diff --git a/src/cmd/5l/obj.c b/src/cmd/5l/obj.c
index 24e6294a84..47831e39c6 100644
--- a/src/cmd/5l/obj.c
+++ b/src/cmd/5l/obj.c
@@ -627,6 +627,38 @@ loop:
 		pc++;
 		goto loop;
 
+	case ANPTRS:
+		if(skip)
+			goto casedef;
+		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 casedef;
+		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:
 		if(cursym != nil && cursym->text) {
 			histtoauto();
@@ -670,6 +702,7 @@ loop:
 		s->text = p;
 		s->value = pc;
 		s->args = p->to.offset2;
+		s->nptrs = -1;
 		lastp = p;
 		p->pc = pc;
 		pc++;