cmd/ld, runtime: restrict stack root scan to locals and arguments

Updates #5134

R=golang-dev, bradfitz, cshapiro, daniel.morsing, ality, iant
CC=golang-dev
https://golang.org/cl/8022044

2 files changed, 11 insertions, 1 deletions

diff --git a/src/cmd/ld/lib.c b/src/cmd/ld/lib.c
index aa0360bea6..1bd2d4ff88 100644
--- a/src/cmd/ld/lib.c
+++ b/src/cmd/ld/lib.c
@@ -1862,7 +1862,10 @@ genasmsym(void (*put)(Sym*, char*, int, vlong, vlong, int, Sym*))
 		/* frame, locals, args, auto and param after */
 		put(nil, ".frame", 'm', (uint32)s->text->to.offset+PtrSize, 0, 0, 0);
 		put(nil, ".locals", 'm', s->locals, 0, 0, 0);
-		put(nil, ".args", 'm', s->args, 0, 0, 0);
+		if(s->text->textflag & NOSPLIT)
+			put(nil, ".args", 'm', ArgsSizeUnknown, 0, 0, 0);
+		else
+			put(nil, ".args", 'm', s->args, 0, 0, 0);
 
 		for(a=s->autom; a; a=a->link) {
 			// Emit a or p according to actual offset, even if label is wrong.
diff --git a/src/cmd/ld/lib.h b/src/cmd/ld/lib.h
index 521f12479f..614a35c529 100644
--- a/src/cmd/ld/lib.h
+++ b/src/cmd/ld/lib.h
@@ -71,6 +71,13 @@ enum
 	NHASH = 100003,
 };
 
+enum
+{
+	// This value is known to the garbage collector and should be kept in
+	// sync with runtime/pkg/runtime.h
+	ArgsSizeUnknown = 0x80000000
+};
+
 typedef struct Library Library;
 struct Library
 {