diff -r 6edf35ba05b2 libgo/runtime/go-caller.c
--- a/libgo/runtime/go-caller.c	Tue Jan 29 17:30:28 2013 -0800
+++ b/libgo/runtime/go-caller.c	Wed Jan 30 13:53:47 2013 -0800
@@ -166,16 +166,16 @@
 Caller (int skip)
 {
   struct caller_ret ret;
-  uintptr pc;
+  Location loc;
   int32 n;
-  String fn;
 
   runtime_memclr (&ret, sizeof ret);
-  n = runtime_callers (skip + 1, &pc, 1);
+  n = runtime_callers (skip + 1, &loc, 1);
   if (n < 1)
     return ret;
-  ret.pc = pc;
-  __go_file_line (pc, &fn, &ret.file, &ret.line);
+  ret.pc = loc.pc;
+  ret.file = loc.filename;
+  ret.line = loc.lineno;
   ret.ok = 1;
   return ret;
 }
diff -r 6edf35ba05b2 libgo/runtime/go-callers.c
--- a/libgo/runtime/go-callers.c	Tue Jan 29 17:30:28 2013 -0800
+++ b/libgo/runtime/go-callers.c	Wed Jan 30 13:53:47 2013 -0800
@@ -15,20 +15,37 @@
 
 struct callers_data
 {
-  uintptr *pcbuf;
+  Location *locbuf;
   int index;
   int max;
 };
 
-/* Callback function for backtrace_simple.  Just collect the PC
-   values.  Return zero to continue, non-zero to stop.  */
+/* Callback function for backtrace_full.  Just collect the locations.
+   Return zero to continue, non-zero to stop.  */
 
 static int
-callback (void *data, uintptr_t pc)
+callback (void *data, uintptr_t pc, const char *filename, int lineno,
+	  const char *function)
 {
   struct callers_data *arg = (struct callers_data *) data;
+  Location *loc;
 
-  arg->pcbuf[arg->index] = pc;
+  /* Skip split stack functions.  */
+  if (function != NULL)
+    {
+      const char *p = function;
+
+      if (__builtin_strncmp (p, "___", 3) == 0)
+	++p;
+      if (__builtin_strncmp (p, "__morestack_", 12) == 0)
+	return 0;
+    }
+
+  loc = &arg->locbuf[arg->index];
+  loc->pc = pc;
+  loc->filename = runtime_gostring ((const byte *) filename);
+  loc->function = runtime_gostring ((const byte *) function);
+  loc->lineno = lineno;
   ++arg->index;
   return arg->index >= arg->max;
 }
@@ -47,15 +64,15 @@
 /* Gather caller PC's.  */
 
 int32
-runtime_callers (int32 skip, uintptr *pcbuf, int32 m)
+runtime_callers (int32 skip, Location *locbuf, int32 m)
 {
   struct callers_data data;
 
-  data.pcbuf = pcbuf;
+  data.locbuf = locbuf;
   data.index = 0;
   data.max = m;
-  backtrace_simple (__go_get_backtrace_state (), skip + 1, callback,
-		    error_callback, &data);
+  backtrace_full (__go_get_backtrace_state (), skip + 1, callback,
+		  error_callback, &data);
   return data.index;
 }
 
@@ -65,8 +82,19 @@
 int
 Callers (int skip, struct __go_open_array pc)
 {
+  Location *locbuf;
+  int ret;
+  int i;
+
+  locbuf = (Location *) runtime_mal (pc.__count * sizeof (Location));
+
   /* In the Go 1 release runtime.Callers has an off-by-one error,
      which we can not correct because it would break backward
      compatibility.  Adjust SKIP here to be compatible.  */
-  return runtime_callers (skip - 1, (uintptr *) pc.__values, pc.__count);
+  ret = runtime_callers (skip - 1, locbuf, pc.__count);
+
+  for (i = 0; i < ret; i++)
+    ((uintptr *) pc.__values)[i] = locbuf[i].pc;
+
+  return ret;
 }
diff -r 6edf35ba05b2 libgo/runtime/go-traceback.c
--- a/libgo/runtime/go-traceback.c	Tue Jan 29 17:30:28 2013 -0800
+++ b/libgo/runtime/go-traceback.c	Wed Jan 30 13:53:47 2013 -0800
@@ -13,29 +13,25 @@
 void
 runtime_traceback ()
 {
-  uintptr pcbuf[100];
+  Location locbuf[100];
   int32 c;
 
-  c = runtime_callers (1, pcbuf, sizeof pcbuf / sizeof pcbuf[0]);
-  runtime_printtrace (pcbuf, c, true);
+  c = runtime_callers (1, locbuf, nelem (locbuf));
+  runtime_printtrace (locbuf, c, true);
 }
 
 void
-runtime_printtrace (uintptr *pcbuf, int32 c, bool current)
+runtime_printtrace (Location *locbuf, int32 c, bool current)
 {
   int32 i;
 
   for (i = 0; i < c; ++i)
     {
-      String fn;
-      String file;
-      intgo line;
-
-      if (__go_file_line (pcbuf[i], &fn, &file, &line)
-	  && runtime_showframe (fn, current))
+      if (runtime_showframe (locbuf[i].function, current))
 	{
-	  runtime_printf ("%S\n", fn);
-	  runtime_printf ("\t%S:%D\n", file, (int64) line);
+	  runtime_printf ("%S\n", locbuf[i].function);
+	  runtime_printf ("\t%S:%D\n", locbuf[i].filename,
+			  (int64) locbuf[i].lineno);
 	}
     }
 }
diff -r 6edf35ba05b2 libgo/runtime/mprof.goc
--- a/libgo/runtime/mprof.goc	Tue Jan 29 17:30:28 2013 -0800
+++ b/libgo/runtime/mprof.goc	Wed Jan 30 13:53:47 2013 -0800
@@ -11,6 +11,7 @@
 #include "malloc.h"
 #include "defs.h"
 #include "go-type.h"
+#include "go-string.h"
 
 // NOTE(rsc): Everything here could use cas if contention became an issue.
 static Lock proflock;
@@ -46,7 +47,7 @@
 	};
 	uintptr	hash;
 	uintptr	nstk;
-	uintptr	stk[1];
+	Location stk[1];
 };
 enum {
 	BuckHashSize = 179999,
@@ -58,9 +59,9 @@
 
 // Return the bucket for stk[0:nstk], allocating new bucket if needed.
 static Bucket*
-stkbucket(int32 typ, uintptr *stk, int32 nstk, bool alloc)
+stkbucket(int32 typ, Location *stk, int32 nstk, bool alloc)
 {
-	int32 i;
+	int32 i, j;
 	uintptr h;
 	Bucket *b;
 
@@ -72,7 +73,7 @@
 	// Hash stack.
 	h = 0;
 	for(i=0; i<nstk; i++) {
-		h += stk[i];
+		h += stk[i].pc;
 		h += h<<10;
 		h ^= h>>6;
 	}
@@ -80,10 +81,18 @@
 	h ^= h>>11;
 
 	i = h%BuckHashSize;
-	for(b = buckhash[i]; b; b=b->next)
-		if(b->typ == typ && b->hash == h && b->nstk == (uintptr)nstk &&
-		   runtime_mcmp((byte*)b->stk, (byte*)stk, nstk*sizeof stk[0]) == 0)
-			return b;
+	for(b = buckhash[i]; b; b=b->next) {
+		if(b->typ == typ && b->hash == h && b->nstk == (uintptr)nstk) {
+			for(j = 0; j < nstk; j++) {
+				if(b->stk[j].pc != stk[j].pc ||
+				   b->stk[j].lineno != stk[j].lineno ||
+				   !__go_strings_equal(b->stk[j].filename, stk[j].filename))
+					break;
+			}
+			if (j == nstk)
+				return b;
+		}
+	}
 
 	if(!alloc)
 		return nil;
@@ -241,7 +250,7 @@
 {
 	M *m;
 	int32 nstk;
-	uintptr stk[32];
+	Location stk[32];
 	Bucket *b;
 
 	m = runtime_m();
@@ -298,7 +307,7 @@
 {
 	int32 nstk;
 	int64 rate;
-	uintptr stk[32];
+	Location stk[32];
 	Bucket *b;
 
 	if(cycles <= 0)
@@ -336,7 +345,7 @@
 	r->alloc_objects = b->allocs;
 	r->free_objects = b->frees;
 	for(i=0; i<b->nstk && i<nelem(r->stk); i++)
-		r->stk[i] = b->stk[i];
+		r->stk[i] = b->stk[i].pc;
 	for(; i<nelem(r->stk); i++)
 		r->stk[i] = 0;
 }
@@ -396,7 +405,7 @@
 			r->count = b->count;
 			r->cycles = b->cycles;
 			for(i=0; (uintptr)i<b->nstk && (uintptr)i<nelem(r->stk); i++)
-				r->stk[i] = b->stk[i];
+				r->stk[i] = b->stk[i].pc;
 			for(; (uintptr)i<nelem(r->stk); i++)
 				r->stk[i] = 0;			
 		}
@@ -413,6 +422,7 @@
 func ThreadCreateProfile(p Slice) (n int, ok bool) {
 	TRecord *r;
 	M *first, *mp;
+	int32 i;
 	
 	first = runtime_atomicloadp(&runtime_allm);
 	n = 0;
@@ -423,7 +433,9 @@
 		ok = true;
 		r = (TRecord*)p.__values;
 		for(mp=first; mp; mp=mp->alllink) {
-			runtime_memmove(r->stk, mp->createstack, sizeof r->stk);
+			for(i = 0; (uintptr)i < nelem(r->stk); i++) {
+				r->stk[i] = mp->createstack[i].pc;
+			}
 			r++;
 		}
 	}
@@ -473,10 +485,14 @@
 static void
 saveg(G *gp, TRecord *r)
 {
-	int32 n;
+	int32 n, i;
+	Location locstk[nelem(r->stk)];
 
-	if(gp == runtime_g())
-		n = runtime_callers(0, r->stk, nelem(r->stk));
+	if(gp == runtime_g()) {
+		n = runtime_callers(0, locstk, nelem(r->stk));
+		for(i = 0; i < n; i++)
+			r->stk[i] = locstk[i].pc;
+	}
 	else {
 		// FIXME: Not implemented.
 		n = 0;
diff -r 6edf35ba05b2 libgo/runtime/proc.c
--- a/libgo/runtime/proc.c	Tue Jan 29 17:30:28 2013 -0800
+++ b/libgo/runtime/proc.c	Wed Jan 30 13:53:47 2013 -0800
@@ -631,7 +631,7 @@
 struct Traceback
 {
 	G* gp;
-	uintptr pcbuf[100];
+	Location locbuf[100];
 	int32 c;
 };
 
@@ -677,7 +677,7 @@
 			runtime_gogo(gp);
 		}
 
-		runtime_printtrace(tb.pcbuf, tb.c, false);
+		runtime_printtrace(tb.locbuf, tb.c, false);
 		runtime_goroutinetrailer(gp);
 	}
 }
@@ -692,8 +692,8 @@
 
 	traceback = gp->traceback;
 	gp->traceback = nil;
-	traceback->c = runtime_callers(1, traceback->pcbuf,
-		sizeof traceback->pcbuf / sizeof traceback->pcbuf[0]);
+	traceback->c = runtime_callers(1, traceback->locbuf,
+		sizeof traceback->locbuf / sizeof traceback->locbuf[0]);
 	runtime_gogo(traceback->gp);
 }
 
@@ -1742,13 +1742,14 @@
 	void (*fn)(uintptr*, int32);
 	int32 hz;
 	uintptr pcbuf[100];
+	Location locbuf[100];
 } prof;
 
 // Called if we receive a SIGPROF signal.
 void
 runtime_sigprof()
 {
-	int32 n;
+	int32 n, i;
 
 	if(prof.fn == nil || prof.hz == 0)
 		return;
@@ -1758,7 +1759,9 @@
 		runtime_unlock(&prof);
 		return;
 	}
-	n = runtime_callers(0, prof.pcbuf, nelem(prof.pcbuf));
+	n = runtime_callers(0, prof.locbuf, nelem(prof.locbuf));
+	for(i = 0; i < n; i++)
+		prof.pcbuf[i] = prof.locbuf[i].pc;
 	if(n > 0)
 		prof.fn(prof.pcbuf, n);
 	runtime_unlock(&prof);
diff -r 6edf35ba05b2 libgo/runtime/runtime.h
--- a/libgo/runtime/runtime.h	Tue Jan 29 17:30:28 2013 -0800
+++ b/libgo/runtime/runtime.h	Wed Jan 30 13:53:47 2013 -0800
@@ -83,6 +83,8 @@
 
 typedef struct  Traceback	Traceback;
 
+typedef struct	Location	Location;
+
 /*
  * Per-CPU declaration.
  */
@@ -155,6 +157,16 @@
 	uint64	nosyield;
 	uint64	nsleep;
 };
+
+// A location in the program, used for backtraces.
+struct	Location
+{
+	uintptr	pc;
+	String	filename;
+	String	function;
+	intgo	lineno;
+};
+
 struct	G
 {
 	Defer*	defer;
@@ -226,7 +238,7 @@
 	MCache	*mcache;
 	G*	lockedg;
 	G*	idleg;
-	uintptr	createstack[32];	// Stack that created this thread.
+	Location createstack[32];	// Stack that created this thread.
 	M*	nextwaitm;	// next M waiting for lock
 	uintptr	waitsema;	// semaphore for parking on locks
 	uint32	waitsemacount;
@@ -391,7 +403,8 @@
 void	runtime_goroutinetrailer(G*);
 void	runtime_traceback();
 void	runtime_tracebackothers(G*);
-void	runtime_printtrace(uintptr*, int32, bool);
+void	runtime_printtrace(Location*, int32, bool);
+String	runtime_gostring(const byte*);
 String	runtime_gostringnocopy(const byte*);
 void*	runtime_mstart(void*);
 G*	runtime_malg(int32, byte**, size_t*);
@@ -406,7 +419,7 @@
 void	runtime_exitsyscall(void) __asm__ (GOSYM_PREFIX "syscall.Exitsyscall");
 void	siginit(void);
 bool	__go_sigsend(int32 sig);
-int32	runtime_callers(int32, uintptr*, int32);
+int32	runtime_callers(int32, Location*, int32);
 int64	runtime_nanotime(void);
 int64	runtime_cputicks(void);
 int64	runtime_tickspersecond(void);
diff -r 6edf35ba05b2 libgo/runtime/string.goc
--- a/libgo/runtime/string.goc	Tue Jan 29 17:30:28 2013 -0800
+++ b/libgo/runtime/string.goc	Wed Jan 30 13:53:47 2013 -0800
@@ -10,6 +10,8 @@
 
 #define charntorune(pv, str, len) __go_get_rune(str, len, pv)
 
+const String	runtime_emptystring;
+
 intgo
 runtime_findnull(const byte *s)
 {
@@ -18,6 +20,38 @@
 	return __builtin_strlen((const char*) s);
 }
 
+static String
+gostringsize(intgo l, byte** pmem)
+{
+	String s;
+	byte *mem;
+
+	if(l == 0) {
+		*pmem = nil;
+		return runtime_emptystring;
+	}
+	// leave room for NUL for C runtime (e.g., callers of getenv)
+	mem = runtime_mallocgc(l+1, FlagNoPointers, 1, 0);
+	s.str = mem;
+	s.len = l;
+	mem[l] = 0;
+	*pmem = mem;
+	return s;
+}
+
+String
+runtime_gostring(const byte *str)
+{
+	intgo l;
+	String s;
+	byte *mem;
+
+	l = runtime_findnull(str);
+	s = gostringsize(l, &mem);
+	runtime_memmove(mem, str, l);
+	return s;
+}
+
 String
 runtime_gostringnocopy(const byte *str)
 {
