code coverage tool

	$ 6cov -g 235.go 6.out
	235.go:62,62 main·main 0x27c9-0x2829 MOVL	$main·.stringo(SB),AX
	235.go:30,30 main·main 0x2856-0x285e ADDQ	$6c0,SP
	$

and assorted fixes.

R=r
DELTA=743  (732 added, 8 deleted, 3 changed)
OCL=19226
CL=19243

src/cmd/cov/Makefile

+# Copyright 2009 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+include ../../Make.conf
+
+# The directory is cov because the source is portable and general.
+# We call the binary 6cov to avoid confusion and because this binary
+# is linked only with amd64 and x86 support.
+
+TARG=6cov
+OFILES=\
+	main.$O\
+	tree.$O\
+
+HFILES=\
+	tree.h\
+
+$(TARG): $(OFILES)
+	$(LD) -o $(TARG) -L$(GOROOT)/lib $(OFILES) -lmach_amd64 -lregexp9 -lbio -l9
+
+clean:
+	rm -f $(OFILES) $(TARG)
+
+install: $(TARG)
+	cp $(TARG) $(BIN)/$(TARG)
+
+$(OFILES): $(HFILES)

src/cmd/cov/main.c

+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+ * code coverage
+ */
+
+#include <u.h>
+#include <time.h>
+#include <libc.h>
+#include <bio.h>
+#include <ctype.h>
+#include <regexp9.h>
+#include "tree.h"
+
+#include <ureg_amd64.h>
+#include <mach_amd64.h>
+typedef struct Ureg Ureg;
+
+void
+usage(void)
+{
+	fprint(2, "usage: cov 6.out [-lv] [-g regexp] [args...]\n");
+	fprint(2, "-g specifies pattern of interesting functions or files\n");
+	exits("usage");
+}
+
+typedef struct Range Range;
+struct Range
+{
+	uvlong pc;
+	uvlong epc;
+};
+
+int chatty;
+int fd;
+int longnames;
+int pid;
+Map *mem;
+Map *text;
+Fhdr fhdr;
+Reprog *grep;
+char cwd[1000];
+int ncwd;
+
+Tree breakpoints;	// code ranges not run
+
+/*
+ * comparison for Range structures
+ * they are "equal" if they overlap, so
+ * that a search for [pc, pc+1) finds the
+ * Range containing pc.
+ */
+int
+rangecmp(void *va, void *vb)
+{
+	Range *a = va, *b = vb;
+	if(a->epc <= b->pc)
+		return 1;
+	if(b->epc <= a->pc)
+		return -1;
+	return 0;
+}
+
+/*
+ * remember that we ran the section of code [pc, epc).
+ */
+void
+ran(uvlong pc, uvlong epc)
+{
+	Range key;
+	Range *r;
+	uvlong oldepc;
+
+	if(chatty)
+		print("run %#llux-%#llux\n", pc, epc);
+
+	key.pc = pc;
+	key.epc = pc+1;
+	r = treeget(&breakpoints, &key);
+	if(r == nil)
+		sysfatal("unchecked breakpoint at %#lux+%d", pc, (int)(epc-pc));
+
+	// Might be that the tail of the sequence
+	// was run already, so r->epc is before the end.
+	// Adjust len.
+	if(epc > r->epc)
+		epc = r->epc;
+
+	if(r->pc == pc) {
+		r->pc = epc;
+	} else {
+		// Chop r to before pc;
+		// add new entry for after if needed.
+		// Changing r->epc does not affect r's position in the tree.
+		oldepc = r->epc;
+		r->epc = pc;
+		if(epc < oldepc) {
+			Range *n;
+			n = malloc(sizeof *n);
+			n->pc = epc;
+			n->epc = oldepc;
+			treeput(&breakpoints, n, n);
+		}
+	}
+}
+
+/*
+ * if s is in the current directory or below,
+ * return the relative path.
+ */
+char*
+shortname(char *s)
+{
+	if(!longnames && strlen(s) > ncwd && memcmp(s, cwd, ncwd) == 0 && s[ncwd] == '/')
+		return s+ncwd+1;
+	return s;
+}
+
+/*
+ * we've decided that [pc, epc) did not run.
+ * do something about it.
+ */
+void
+missing(uvlong pc, uvlong epc)
+{
+	char src1[1000];
+	char src2[1000];
+	char buf[100];
+	Symbol s;
+	char *p;
+
+	if(!findsym(pc, CTEXT, &s) || !fileline(src1, sizeof src1, pc) || !fileline(src2, sizeof src2, pc)) {
+		print("%#llux-%#llux\n", pc, epc);
+		return;
+	}
+
+	if(pc == s.value) {
+		// never entered function
+		print("%s %s never called (%#llux-%#llux)\n", shortname(src1), s.name, pc, epc);
+		return;
+	}
+	if(pc <= s.value+13) {
+		// probably stub for stack growth.
+		// check whether last instruction is call to morestack.
+		// the -5 below is the length of
+		//	CALL sys.morestack.
+		buf[0] = 0;
+		machdata->das(text, epc-5, 0, buf, sizeof buf);
+		if(strstr(buf, "morestack"))
+			return;
+	}
+
+	if(epc - pc == 5) {
+		// check for CALL sys.throwindex
+		buf[0] = 0;
+		machdata->das(text, pc, 0, buf, sizeof buf);
+		if(strstr(buf, "throwindex"))
+			return;
+	}
+
+	// show first instruction to make clear where we were.
+	machdata->das(text, pc, 0, buf, sizeof buf);
+
+	// cut filename off src2, leaving just line number.
+	p = strrchr(src2, ':');
+	if(p != nil)
+		p++;
+	else
+		p = src2;
+	print("%s,%s %s %#llux-%#llux %s\n", shortname(src1), p, s.name, pc, epc, buf);
+}
+
+/*
+ * walk the tree, calling missing for each non-empty
+ * section of missing code.
+ */
+void
+walktree(TreeNode *t)
+{
+	Range *n;
+
+	if(t == nil)
+		return;
+	walktree(t->left);
+	n = t->key;
+	if(n->pc < n->epc)
+		missing(n->pc, n->epc);
+	walktree(t->right);
+}
+
+/*
+ * set a breakpoint all over [pc, epc)
+ * and remember that we did.
+ */
+void
+breakpoint(uvlong pc, uvlong epc)
+{
+	Range *r;
+
+	r = malloc(sizeof *r);
+	r->pc = pc;
+	r->epc = epc;
+	treeput(&breakpoints, r, r);
+
+	for(; pc < epc; pc+=machdata->bpsize)
+		put1(mem, pc, machdata->bpinst, machdata->bpsize);
+}
+
+/*
+ * install breakpoints over all text symbols
+ * that match the pattern.
+ */
+void
+cover(void)
+{
+	Symbol s;
+	char *lastfn;
+	uvlong lastpc;
+	int i;
+	char buf[200];
+
+	lastfn = nil;
+	lastpc = 0;
+	for(i=0; textsym(&s, i); i++) {
+		switch(s.type) {
+		case 'T':
+		case 't':
+			if(lastpc != 0) {
+				breakpoint(lastpc, s.value);
+				lastpc = 0;
+			}
+			// Ignore second entry for a given name;
+			// that's the debugging blob.
+			if(lastfn && strcmp(s.name, lastfn) == 0)
+				break;
+			lastfn = s.name;
+			buf[0] = 0;
+			fileline(buf, sizeof buf, s.value);
+			if(grep == nil || regexec9(grep, buf, nil, 0) > 0 || regexec9(grep, s.name, nil, 0) > 0)
+				lastpc = s.value;
+		}
+	}
+}
+
+uvlong
+rgetzero(Map *map, char *reg)
+{
+	return 0;
+}
+
+/*
+ * remove the breakpoints at pc and successive instructions,
+ * up to and including the first jump or other control flow transfer.
+ */
+void
+uncover(uvlong pc)
+{
+	uchar buf[1000];
+	int n, n1, n2;
+	uvlong foll[2];
+
+	// Double-check that we stopped at a breakpoint.
+	if(get1(mem, pc, buf, machdata->bpsize) < 0)
+		sysfatal("read mem inst at %#llux: %r", pc);
+	if(memcmp(buf, machdata->bpinst, machdata->bpsize) != 0)
+		sysfatal("stopped at %#llux; not at breakpoint %d", pc, machdata->bpsize);
+
+	// Figure out how many bytes of straight-line code
+	// there are in the text starting at pc.
+	n = 0;
+	while(n < sizeof buf) {
+		n1 = machdata->instsize(text, pc+n);
+		if(n+n1 > sizeof buf)
+			break;
+		n2 = machdata->foll(text, pc+n, rgetzero, foll);
+		n += n1;
+		if(n2 != 1 || foll[0] != pc+n)
+			break;
+	}
+
+	// Record that this section of code ran.
+	ran(pc, pc+n);
+
+	// Put original instructions back.
+	if(get1(text, pc, buf, n) < 0)
+		sysfatal("get1: %r");
+	if(put1(mem, pc, buf, n) < 0)
+		sysfatal("put1: %r");
+}
+
+int
+startprocess(char **argv)
+{
+	int pid;
+
+	if((pid = fork()) < 0)
+		sysfatal("fork: %r");
+	if(pid == 0) {
+		pid = getpid();
+		if(ctlproc(pid, "hang") < 0)
+			sysfatal("ctlproc hang: %r");
+		execv(argv[0], argv);
+		sysfatal("exec %s: %r", argv[0]);
+	}
+	if(ctlproc(pid, "attached") < 0 || ctlproc(pid, "waitstop") < 0)
+		sysfatal("attach %d %s: %r", pid, argv[0]);
+	return pid;
+}
+
+int
+go(void)
+{
+	uvlong pc;
+	char buf[100];
+	int n;
+
+	for(n = 0;; n++) {
+		ctlproc(pid, "startstop");
+		if(get8(mem, offsetof(Ureg, ip), &pc) < 0) {
+			rerrstr(buf, sizeof buf);
+			if(strstr(buf, "exited") || strstr(buf, "No such process"))
+				return n;
+			sysfatal("cannot read pc: %r");
+		}
+		pc--;
+		if(put8(mem, offsetof(Ureg, ip), pc) < 0)
+			sysfatal("cannot write pc: %r");
+		uncover(pc);
+	}
+}
+
+void
+main(int argc, char **argv)
+{
+	int n;
+	char *regexp;
+
+	ARGBEGIN{
+	case 'g':
+		regexp = EARGF(usage());
+		if((grep = regcomp9(regexp)) == nil)
+			sysfatal("bad regexp %s", regexp);
+		break;
+	case 'l':
+		longnames++;
+		break;
+	case 'v':
+		chatty++;
+		break;
+	default:
+		usage();
+	}ARGEND
+
+	getwd(cwd, sizeof cwd);
+	ncwd = strlen(cwd);
+
+	if(argc < 1)
+		usage();
+	fd = open(argv[0], OREAD);
+	if(fd < 0)
+		sysfatal("open %s: %r", argv[0]);
+	if(crackhdr(fd, &fhdr) <= 0)
+		sysfatal("crackhdr: %r");
+	machbytype(fhdr.type);
+	if(syminit(fd, &fhdr) <= 0)
+		sysfatal("syminit: %r");
+	text = loadmap(nil, fd, &fhdr);
+	if(text == nil)
+		sysfatal("loadmap: %r");
+	pid = startprocess(argv);
+	mem = attachproc(pid, &fhdr);
+	if(mem == nil)
+		sysfatal("attachproc: %r");
+	breakpoints.cmp = rangecmp;
+	cover();
+	n = go();
+	walktree(breakpoints.root);
+	if(chatty)
+		print("%d breakpoints\n", n);
+	detachproc(mem);
+	exits(0);
+}
+

src/cmd/cov/tree.c

+// Renamed from Map to Tree to avoid conflict with libmach.
+
+/*
+Copyright (c) 2003-2007 Russ Cox, Tom Bergan, Austin Clements,
+                        Massachusetts Institute of Technology
+Portions Copyright (c) 2009 The Go Authors. All rights reserved.
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+*/
+
+// Mutable map structure, but still based on
+// Okasaki, Red Black Trees in a Functional Setting, JFP 1999,
+// which is a lot easier than the traditional red-black
+// and plenty fast enough for me.  (Also I could copy
+// and edit fmap.c.)
+
+#include <u.h>
+#include <libc.h>
+#include "tree.h"
+
+#define TreeNode TreeNode
+#define Tree Tree
+
+enum
+{
+	Red = 0,
+	Black = 1
+};
+
+
+// Red-black trees are binary trees with this property:
+//	1. No red node has a red parent.
+//	2. Every path from the root to a leaf contains the
+//		same number of black nodes.
+
+static TreeNode*
+rwTreeNode(TreeNode *p, int color, TreeNode *left, void *key, void *value, TreeNode *right)
+{
+	if(p == nil)
+		p = malloc(sizeof *p);
+	p->color = color;
+	p->left = left;
+	p->key = key;
+	p->value = value;
+	p->right = right;
+	return p;
+}
+
+static TreeNode*
+balance(TreeNode *m0)
+{
+	void *xk, *xv, *yk, *yv, *zk, *zv;
+	TreeNode *a, *b, *c, *d;
+	TreeNode *m1, *m2;
+	int color;
+	TreeNode *left, *right;
+	void *key, *value;
+
+	color = m0->color;
+	left = m0->left;
+	key = m0->key;
+	value = m0->value;
+	right = m0->right;
+
+	// Okasaki notation: (T is mkTreeNode, B is Black, R is Red, x, y, z are key-value.
+	//
+	// balance B (T R (T R a x b) y c) z d
+	// balance B (T R a x (T R b y c)) z d
+	// balance B a x (T R (T R b y c) z d)
+	// balance B a x (T R b y (T R c z d))
+	//
+	//     = T R (T B a x b) y (T B c z d)
+
+	if(color == Black){
+		if(left && left->color == Red){
+			if(left->left && left->left->color == Red){
+				a = left->left->left;
+				xk = left->left->key;
+				xv = left->left->value;
+				b = left->left->right;
+				yk = left->key;
+				yv = left->value;
+				c = left->right;
+				zk = key;
+				zv = value;
+				d = right;
+				m1 = left;
+				m2 = left->left;
+				goto hard;
+			}else if(left->right && left->right->color == Red){
+				a = left->left;
+				xk = left->key;
+				xv = left->value;
+				b = left->right->left;
+				yk = left->right->key;
+				yv = left->right->value;
+				c = left->right->right;
+				zk = key;
+				zv = value;
+				d = right;
+				m1 = left;
+				m2 = left->right;
+				goto hard;
+			}
+		}else if(right && right->color == Red){
+			if(right->left && right->left->color == Red){
+				a = left;
+				xk = key;
+				xv = value;
+				b = right->left->left;
+				yk = right->left->key;
+				yv = right->left->value;
+				c = right->left->right;
+				zk = right->key;
+				zv = right->value;
+				d = right->right;
+				m1 = right;
+				m2 = right->left;
+				goto hard;
+			}else if(right->right && right->right->color == Red){
+				a = left;
+				xk = key;
+				xv = value;
+				b = right->left;
+				yk = right->key;
+				yv = right->value;
+				c = right->right->left;
+				zk = right->right->key;
+				zv = right->right->value;
+				d = right->right->right;
+				m1 = right;
+				m2 = right->right;
+				goto hard;
+			}
+		}
+	}
+	return rwTreeNode(m0, color, left, key, value, right);
+
+hard:
+	return rwTreeNode(m0, Red, rwTreeNode(m1, Black, a, xk, xv, b),
+		yk, yv, rwTreeNode(m2, Black, c, zk, zv, d));
+}
+
+static TreeNode*
+ins0(TreeNode *p, void *k, void *v, TreeNode *rw)
+{
+	if(p == nil)
+		return rwTreeNode(rw, Red, nil, k, v, nil);
+	if(p->key == k){
+		if(rw)
+			return rwTreeNode(rw, p->color, p->left, k, v, p->right);
+		p->value = v;
+		return p;
+	}
+	if(p->key < k)
+		p->left = ins0(p->left, k, v, rw);
+	else
+		p->right = ins0(p->right, k, v, rw);
+	return balance(p);
+}
+
+static TreeNode*
+ins1(Tree *m, TreeNode *p, void *k, void *v, TreeNode *rw)
+{
+	int i;
+
+	if(p == nil)
+		return rwTreeNode(rw, Red, nil, k, v, nil);
+	i = m->cmp(p->key, k);
+	if(i == 0){
+		if(rw)
+			return rwTreeNode(rw, p->color, p->left, k, v, p->right);
+		p->value = v;
+		return p;
+	}
+	if(i < 0)
+		p->left = ins1(m, p->left, k, v, rw);
+	else
+		p->right = ins1(m, p->right, k, v, rw);
+	return balance(p);
+}
+
+void
+treeputelem(Tree *m, void *key, void *val, TreeNode *rw)
+{
+	if(m->cmp)
+		m->root = ins1(m, m->root, key, val, rw);
+	else
+		m->root = ins0(m->root, key, val, rw);
+}
+
+void
+treeput(Tree *m, void *key, void *val)
+{
+	treeputelem(m, key, val, nil);
+}
+
+void*
+treeget(Tree *m, void *key)
+{
+	int i;
+	TreeNode *p;
+
+	p = m->root;
+	if(m->cmp){
+		for(;;){
+			if(p == nil)
+				return nil;
+			i = m->cmp(p->key, key);
+			if(i < 0)
+				p = p->left;
+			else if(i > 0)
+				p = p->right;
+			else
+				return p->value;
+		}
+	}else{
+		for(;;){
+			if(p == nil)
+				return nil;
+			if(p->key == key)
+				return p->value;
+			if(p->key < key)
+				p = p->left;
+			else
+				p = p->right;
+		}
+	}
+}

src/cmd/cov/tree.h

+// Renamed from Map to Tree to avoid conflict with libmach.
+
+/*
+Copyright (c) 2003-2007 Russ Cox, Tom Bergan, Austin Clements,
+                        Massachusetts Institute of Technology
+Portions Copyright (c) 2009 The Go Authors. All rights reserved.
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+*/
+
+typedef struct Tree Tree;
+typedef struct TreeNode TreeNode;
+struct Tree
+{
+        int (*cmp)(void*, void*);
+        TreeNode *root;
+};
+
+struct TreeNode
+{
+        int color;
+        TreeNode *left;
+        void *key;
+        void *value;
+        TreeNode *right;
+};
+
+void *treeget(Tree*, void*);
+void treeput(Tree*, void*, void*);
+void treeputelem(Tree*, void*, void*, TreeNode*);

src/cmd/prof/Makefile

@@ -4,7 +4,7 @@
 
 include ../../Make.conf
 
-# The directory is db because the source is portable and general.
+# The directory is prof because the source is portable and general.
 # We call the binary 6prof to avoid confusion and because this binary
 # is linked only with amd64 and x86 support.
 

src/libmach_amd64/darwin.c

@@ -31,6 +31,7 @@
 #include <mach_amd64.h>
 #include <ureg_amd64.h>
 typedef struct Ureg Ureg;
+#undef waitpid	/* want Unix waitpid, not Plan 9 */
 
 extern mach_port_t mach_reply_port(void);	// should be in system headers, is not
 
@@ -185,6 +186,7 @@ static int nthr;
 static pthread_mutex_t mu;
 static pthread_cond_t cond;
 static void* excthread(void*);
+static void* waitthread(void*);
 static mach_port_t excport;
 
 enum {
@@ -215,9 +217,10 @@ addpid(int pid, int force)
 		pthread_t p;
 
 		excport = mach_reply_port();
-		pthread_create(&p, nil, excthread, nil);
 		pthread_mutex_init(&mu, nil);
 		pthread_cond_init(&cond, nil);
+		pthread_create(&p, nil, excthread, nil);
+		pthread_create(&p, nil, waitthread, (void*)(uintptr)pid);
 		first = 0;
 	}
 
@@ -483,6 +486,7 @@ machregrw(Map *map, Seg *seg, uvlong addr, void *v, uint n, int isr)
 	uint nn;
 	mach_port_t thread;
 	int reg;
+	char buf[100];
 	union {
 		x86_thread_state64_t regs;
 		uchar p[1];
@@ -517,6 +521,10 @@ machregrw(Map *map, Seg *seg, uvlong addr, void *v, uint n, int isr)
 	if(me(thread_get_state(thread, x86_THREAD_STATE64, (thread_state_t)&u.regs, &nn)) < 0){
 		if(!isr)
 			thread_resume(thread);
+		rerrstr(buf, sizeof buf);
+		if(strcmp(buf, "send invalid dest") == 0)
+			werrstr("process exited");
+		else
 			werrstr("thread_get_state: %r");
 		return -1;
 	}
@@ -636,14 +644,15 @@ havet:
 		ncode = nelem(t->code);
 	memmove(t->code, code, ncode*sizeof t->code[0]);
 
+	// Suspend thread, so that we can look at it & restart it later.
+	if(me(thread_suspend(thread)) < 0)
+		fprint(2, "catch_exception_raise thread_suspend: %r\n");
+
 	// Synchronize with waitstop below.
 	pthread_mutex_lock(&mu);
 	pthread_cond_broadcast(&cond);
 	pthread_mutex_unlock(&mu);
 
-	// Suspend thread, so that we can look at it & restart it later.
-	if(me(thread_suspend(thread)) < 0)
-		fprint(2, "catch_exception_raise thread_suspend: %r\n");
 	return KERN_SUCCESS;
 }
 
@@ -656,12 +665,29 @@ excthread(void *v)
 	return 0;
 }
 
+// Wait for pid to exit.
+static int exited;
+static void*
+waitthread(void *v)
+{
+	int pid, status;
+
+	pid = (int)(uintptr)v;
+	waitpid(pid, &status, 0);
+	exited = 1;
+	// Synchronize with waitstop below.
+	pthread_mutex_lock(&mu);
+	pthread_cond_broadcast(&cond);
+	pthread_mutex_unlock(&mu);
+	return nil;
+}
+
 // Wait for thread t to stop.
 static int
 waitstop(Thread *t)
 {
 	pthread_mutex_lock(&mu);
-	while(!threadstopped(t))
+	while(!exited && !threadstopped(t))
 		pthread_cond_wait(&cond, &mu);
 	pthread_mutex_unlock(&mu);
 	return 0;

src/libmach_amd64/sym.c

@@ -1163,6 +1163,8 @@ fileelem(Sym **fp, uchar *cp, char *buf, int n)
 	bp = buf;
 	end = buf+n-1;
 	for(i = 1; j = (cp[i]<<8)|cp[i+1]; i+=2){
+		if(j >= fmaxi)	// TODO(rsc): should not happen, but does!
+			break;
 		c = fp[j]->name;
 		if(bp != buf && bp[-1] != '/' && bp < end)
 			*bp++ = '/';