src/pkg/runtime/malloc.h     |  6 +++---
 src/pkg/runtime/mcentral.c   |  1 -
 src/pkg/runtime/mgc0.c       |  7 +++++--
 src/pkg/runtime/mheap.c      |  1 -
 src/pkg/runtime/mheapmap32.c |  1 -
 src/pkg/runtime/mheapmap64.c |  2 --
 src/pkg/runtime/proc.c       |  3 ++-
 src/pkg/runtime/symtab.c     | 39 +++++----------------------------------

diff --git a/src/pkg/runtime/malloc.h b/src/pkg/runtime/malloc.h
index 2e0f1143dd91107f5e3055e7801b93227779e496..b3fa8e0dfb2036d8a7bacc1410117352b9bc77e3 100644
--- a/src/pkg/runtime/malloc.h
+++ b/src/pkg/runtime/malloc.h
@@ -113,8 +113,9 @@ {
 	MLink *next;
 };
 
-// SysAlloc obtains a large chunk of memory from the operating system,
-// typically on the order of a hundred kilobytes or a megabyte.
+// SysAlloc obtains a large chunk of zeroed memory from the
+// operating system, typically on the order of a hundred kilobytes
+// or a megabyte.
 //
 // SysUnused notifies the operating system that the contents
 // of the memory region are no longer needed and can be reused
@@ -312,4 +313,3 @@ 	RefNone,		// no references
 	RefSome,		// some references
 	RefNoPointers = 0x80000000U,	// flag - no pointers here     
 };
-
diff --git a/src/pkg/runtime/mcentral.c b/src/pkg/runtime/mcentral.c
index 5c9f720c09a887e5d3f48797f09c47ebd85b7696..9881812e3227fd31622ef0318cab9bcdfd080dea 100644
--- a/src/pkg/runtime/mcentral.c
+++ b/src/pkg/runtime/mcentral.c
@@ -40,7 +40,6 @@ {
 	MLink *first, *last, *v;
 	int32 i;
 
-
 	lock(c);
 	// Replenish central list if empty.
 	if(MSpanList_IsEmpty(&c->nonempty)) {
diff --git a/src/pkg/runtime/mgc0.c b/src/pkg/runtime/mgc0.c
index d01429f349c20cc130c899d1f4285d16d03461a1..f0eafe3fd6cb8279d13ca351de375b8baec92e5f 100644
--- a/src/pkg/runtime/mgc0.c
+++ b/src/pkg/runtime/mgc0.c
@@ -91,8 +91,11 @@ mark(void)
 {
 	G *gp;
 
-	// mark data+bss
-	scanblock(0, data, end - data);
+	// mark data+bss.
+	// skip mheap itself, which has no interesting pointers
+	// and is mostly zeroed and would not otherwise be paged in.
+	scanblock(0, data, (byte*)&mheap - data);
+	scanblock(0, (byte*)(&mheap+1), end - (byte*)(&mheap+1));
 
 	// mark stacks
 	for(gp=allg; gp!=nil; gp=gp->alllink) {
diff --git a/src/pkg/runtime/mheap.c b/src/pkg/runtime/mheap.c
index 8661bd2a1bc207a26f7e2a051fa6ade89efaa343..e78c860c31294a382b251a862e4b6bfb3c497055 100644
--- a/src/pkg/runtime/mheap.c
+++ b/src/pkg/runtime/mheap.c
@@ -194,7 +194,6 @@
 	// NOTE(rsc): In tcmalloc, if we've accumulated enough
 	// system allocations, the heap map gets entirely allocated
 	// in 32-bit mode.  (In 64-bit mode that's not practical.)
-
 	if(!MHeapMap_Preallocate(&h->map, ((uintptr)v>>PageShift) - 1, (ask>>PageShift) + 2)) {
 		SysFree(v, ask);
 		return false;
diff --git a/src/pkg/runtime/mheapmap32.c b/src/pkg/runtime/mheapmap32.c
index 8cea825c33eac934d7816b81e58ebe89cb697024..13491595dad91c4eff96885413639719c8f44cb5 100644
--- a/src/pkg/runtime/mheapmap32.c
+++ b/src/pkg/runtime/mheapmap32.c
@@ -84,7 +84,6 @@ 		if(m->p[i1] == nil) {
 			p2 = m->allocator(sizeof *p2);
 			if(p2 == nil)
 				return false;
-			runtime_memclr((byte*)p2, sizeof *p2);
 			m->p[i1] = p2;
 		}
 
diff --git a/src/pkg/runtime/mheapmap64.c b/src/pkg/runtime/mheapmap64.c
index 79302917863e3af76a5d65c11a33b67f57d5bef4..97e20b6d2085edccfa2b77beaeef24f4afe4399f 100644
--- a/src/pkg/runtime/mheapmap64.c
+++ b/src/pkg/runtime/mheapmap64.c
@@ -96,7 +96,6 @@ 		if((p2 = m->p[i1]) == nil) {
 			p2 = m->allocator(sizeof *p2);
 			if(p2 == nil)
 				return false;
-			runtime_memclr((byte*)p2, sizeof *p2);
 			m->p[i1] = p2;
 		}
 
@@ -105,7 +104,6 @@ 		if(p2->p[i2] == nil) {
 			p3 = m->allocator(sizeof *p3);
 			if(p3 == nil)
 				return false;
-			runtime_memclr((byte*)p3, sizeof *p3);
 			p2->p[i2] = p3;
 		}
 
diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c
index 2f36868f5f88de49c7134fbf97802b902f71a48c..f04cb6692802ac41ce04a8a2e19dcc190ac2f6f5 100644
--- a/src/pkg/runtime/proc.c
+++ b/src/pkg/runtime/proc.c
@@ -102,9 +102,10 @@
 	mallocinit();
 	goargs();
 
+	// For debugging:
 	// Allocate internal symbol table representation now,
 	// so that we don't need to call malloc when we crash.
-	findfunc(0);
+	// findfunc(0);
 
 	sched.gomaxprocs = 1;
 	p = getenv("GOMAXPROCS");
diff --git a/src/pkg/runtime/symtab.c b/src/pkg/runtime/symtab.c
index 18ce07a1cf1c27ee70996d3636e61b274cc3a1be..0b5499474f4785fadf9068cd506083fb477e119c 100644
--- a/src/pkg/runtime/symtab.c
+++ b/src/pkg/runtime/symtab.c
@@ -24,40 +24,6 @@ #define SYMCOUNTS ((int32*)(0x99LL<<24))	// known to 8l
 #define SYMDATA ((byte*)(0x99LL<<24) + 8)
 #endif
 
-
-// Return a pointer to a byte array containing the symbol table segment.
-void
-runtime·symdat(Slice *symtab, Slice *pclntab)
-{
-	Slice *a;
-	int32 *v;
-
-	// TODO(rsc): Remove once TODO at top of file is done.
-	if(goos != nil && strcmp((uint8*)goos, (uint8*)"nacl") == 0) {
-		symtab = mal(sizeof *a);
-		pclntab = mal(sizeof *a);
-		FLUSH(&symtab);
-		FLUSH(&pclntab);
-		return;
-	}
-
-	v = SYMCOUNTS;
-
-	a = mal(sizeof *a);
-	a->len = v[0];
-	a->cap = a->len;
-	a->array = SYMDATA;
-	symtab = a;
-	FLUSH(&symtab);
-
-	a = mal(sizeof *a);
-	a->len = v[1];
-	a->cap = a->len;
-	a->array = SYMDATA + v[0];
-	pclntab = a;
-	FLUSH(&pclntab);
-}
-
 typedef struct Sym Sym;
 struct Sym
 {
@@ -121,6 +87,8 @@ static int32 nfunc;
 
 static byte **fname;
 static int32 nfname;
+
+static Lock funclock;
 
 static void
 dofunc(Sym *sym)
@@ -379,8 +347,11 @@ {
 	Func *f;
 	int32 nf, n;
 
+	lock(&funclock);
 	if(func == nil)
 		buildfuncs();
+	unlock(&funclock);
+
 	if(nfunc == 0)
 		return nil;
 	if(addr < func[0].entry || addr >= func[nfunc].entry)