diff --git a/src/cmd/prof/Makefile b/src/cmd/prof/Makefile
new file mode 100644
index 00000000000..99d292eb427
--- /dev/null
+++ b/src/cmd/prof/Makefile
@@ -0,0 +1,28 @@
+# 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 db 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.
+
+TARG=6prof
+OFILES=\
+	main.$O\
+
+#HFILES=\
+#	defs.h\
+#	fns.h\
+
+$(TARG): $(OFILES)
+	$(LD) -o $(TARG) -L$(GOROOT)/lib $(OFILES) -lmach_amd64 -lbio -l9
+
+clean:
+	rm -f $(OFILES) $(TARG)
+
+install: $(TARG)
+	cp $(TARG) $(BIN)/$(TARG)
+
+$(OFILES): $(HFILES)
diff --git a/src/cmd/prof/main.c b/src/cmd/prof/main.c
new file mode 100644
index 00000000000..cd708e96f7d
--- /dev/null
+++ b/src/cmd/prof/main.c
@@ -0,0 +1,341 @@
+// 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 <u.h>
+#include <libc.h>
+#include <bio.h>
+#include <ctype.h>
+#include <time.h>
+
+#include <ureg_amd64.h>
+#include <mach_amd64.h>
+
+int pid;
+char* file = "6.out";
+static Fhdr fhdr;
+int have_syms;
+int fd;
+Map *map;
+Map	*symmap;
+struct Ureg ureg;
+int total_sec = 10;
+int delta_msec = 100;
+int collapse = 1;	// collapse histogram trace points in same function
+
+// output formats
+int functions;	// print functions
+int histograms;	// print histograms
+int linenums;	// print file and line numbers rather than function names
+int registers;	// print registers
+int stacks;		// print stack traces
+
+void
+Usage()
+{
+	fprint(2, "Usage: prof -p pid [-t total_secs] [-d delta_msec] [6.out]\n");
+	fprint(2, "\tformats (default -h):\n");
+	fprint(2, "\t\t-h: histograms\n");
+	fprint(2, "\t\t-f: dynamic functions\n");
+	fprint(2, "\t\t-l: dynamic file and line numbers\n");
+	fprint(2, "\t\t-r: dynamic registers\n");
+	fprint(2, "\t\t-s: dynamic function stack traces\n");
+	exit(2);
+}
+
+typedef struct PC PC;
+struct PC {
+	uvlong pc;
+	unsigned int count;
+	PC* next;
+};
+
+enum {
+	Ncounters = 256
+};
+
+PC *counters[Ncounters];
+
+void
+regprint(void)
+{
+	print("ax\t0x%llux\n", ureg.ax);
+	print("bx\t0x%llux\n", ureg.bx);
+	print("cx\t0x%llux\n", ureg.cx);
+	print("dx\t0x%llux\n", ureg.dx);
+	print("si\t0x%llux\n", ureg.si);
+	print("di\t0x%llux\n", ureg.di);
+	print("bp\t0x%llux\n", ureg.bp);
+	print("r8\t0x%llux\n", ureg.r8);
+	print("r9\t0x%llux\n", ureg.r9);
+	print("r10\t0x%llux\n", ureg.r10);
+	print("r11\t0x%llux\n", ureg.r11);
+	print("r12\t0x%llux\n", ureg.r12);
+	print("r13\t0x%llux\n", ureg.r13);
+	print("r14\t0x%llux\n", ureg.r14);
+	print("r15\t0x%llux\n", ureg.r15);
+	print("ds\t0x%llux\n", ureg.ds);
+	print("es\t0x%llux\n", ureg.es);
+	print("fs\t0x%llux\n", ureg.fs);
+	print("gs\t0x%llux\n", ureg.gs);
+	print("type\t0x%llux\n", ureg.type);
+	print("error\t0x%llux\n", ureg.error);
+	print("pc\t0x%llux\n", ureg.ip);
+	print("cs\t0x%llux\n", ureg.cs);
+	print("flags\t0x%llux\n", ureg.flags);
+	print("sp\t0x%llux\n", ureg.sp);
+	print("ss\t0x%llux\n", ureg.ss);
+}
+
+int
+sample()
+{
+	int i;
+
+	ctlproc(pid, "stop");
+	for(i = 0; i < sizeof ureg; i+=8) {
+		if(get8(map, (uvlong)i, &((uvlong*)&ureg)[i/8]) < 0) {
+			fprint(2, "prof: can't read registers at %d: %r\n", i);
+			return 0;
+		}
+	}
+	ctlproc(pid, "start");
+	return 1;
+}
+
+uvlong nextpc;
+
+void
+ptrace(Map *map, uvlong pc, uvlong sp, Symbol *sym)
+{
+	char buf[1024];
+	if(nextpc == 0)
+		nextpc = sym->value;
+	print("%s(", sym->name);
+	print(")");
+	if(nextpc != sym->value)
+		print("+%#llux ", nextpc - sym->value);
+	if(have_syms && linenums && fileline(buf, sizeof buf, pc)) {
+		print(" %s", buf);
+	}
+	print("\n");
+	nextpc = pc;
+}
+
+void
+stacktracepcsp(uvlong pc, uvlong sp)
+{
+	nextpc = 0;
+	if(machdata->ctrace==nil)
+		fprint(2, "no machdata->ctrace\n");
+	else if(machdata->ctrace(map, pc, sp, 0, ptrace) <= 0)
+		fprint(2, "no stack frame: pc=%#p sp=%#p\n", pc, sp);
+}
+
+void
+addtohistogram(uvlong pc, uvlong sp)
+{
+	int h;
+	PC *x;
+	
+	h = pc % Ncounters;
+	for(x = counters[h]; x != NULL; x = x->next) {
+		if(x->pc == pc) {
+			x->count++;
+			return;
+		}
+	}
+	x = malloc(sizeof(PC));
+	x->pc = pc;
+	x->count = 1;
+	x->next = counters[h];
+	counters[h] = x;
+}
+
+void
+printpc(uvlong pc, uvlong sp)
+{
+	char buf[1024];
+	if(registers)
+		regprint();
+	if(have_syms > 0 && linenums &&  fileline(buf, sizeof buf, pc))
+		print("%s\n", buf);
+	if(have_syms > 0 && functions) {
+		symoff(buf, sizeof(buf), pc, CANY);
+		print("%s\n", buf);
+	}
+	if(stacks){
+		stacktracepcsp(pc, sp);
+	}
+	if(histograms){
+		addtohistogram(pc, sp);
+	}
+}
+
+void samples()
+{
+	int msec;
+	struct timespec req;
+
+	req.tv_sec = delta_msec/1000;
+	req.tv_nsec = 1000000*(delta_msec % 1000);
+	for(msec = 0; msec < 1000*total_sec; msec += delta_msec) {
+		if(!sample())
+			break;
+		printpc(ureg.ip, ureg.sp);
+		nanosleep(&req, NULL);
+	}
+}
+
+int
+comparepc(const void *va, const void *vb)
+{
+	const PC *const*a = va;
+	const PC *const*b = vb;
+	return (*a)->pc - (*b)->pc;
+}
+
+int
+comparecount(const void *va, const void *vb)
+{
+	const PC *const*a = va;
+	const PC *const*b = vb;
+	return (*b)->count - (*a)->count;  // sort downwards
+}
+
+void
+func(char *s, int n, uvlong pc)
+{
+	char *p;
+
+	symoff(s, n, pc, CANY);
+	p = strchr(s, '+');
+	if(p != NULL)
+		*p = 0;
+}
+
+void
+dumphistogram()
+{
+	int h;
+	PC *x;
+	PC **pcs;
+	uint i;
+	uint j;
+	uint npc;
+	uint ncount;
+	char b1[100];
+	char b2[100];
+
+	if(!histograms)
+		return;
+
+	// count samples
+	ncount = 0;
+	npc = 0;
+	for(h = 0; h < Ncounters; h++)
+		for(x = counters[h]; x != NULL; x = x->next) {
+			ncount += x->count;
+			npc++;
+		}
+	// build array
+	pcs = malloc(npc*sizeof(PC*));
+	i = 0;
+	for(h = 0; h < Ncounters; h++)
+		for(x = counters[h]; x != NULL; x = x->next)
+			pcs[i++] = x;
+	if(collapse) {
+		// combine counts in same function
+		// sort by address
+		qsort(pcs, npc, sizeof(PC*), comparepc);
+		for(i = j = 0; i < npc; i++){
+			x = pcs[i];
+			func(b2, sizeof(b2), x->pc);
+			if(j > 0 && strcmp(b1, b2) == 0) {
+				pcs[i-1]->count += x->count;
+			} else {
+				strcpy(b1, b2);
+				pcs[j++] = x;
+			}
+		}
+		npc = j;
+	}
+	// sort by count
+	qsort(pcs, npc, sizeof(PC*), comparecount);
+	// print array
+	for(i = 0; i < npc; i++){
+		x = pcs[i];
+		print("%5.2f%%\t", 100.0*(double)x->count/(double)ncount);
+		if(collapse)
+			func(b2, sizeof b2, x->pc);
+		else
+			symoff(b2, sizeof(b2), x->pc, CANY);
+		print("%s\n", b2);
+	}
+}
+
+int
+main(int argc, char *argv[])
+{
+	ARGBEGIN{
+	case 'c':
+		collapse = 0;
+		break;
+	case 'd':
+		delta_msec = atoi(EARGF(Usage));
+		break;
+	case 't':
+		total_sec = atoi(EARGF(Usage));
+		break;
+	case 'p':
+		pid = atoi(EARGF(Usage));
+		break;
+	case 'f':
+		functions = 1;
+		break;
+	case 'h':
+		histograms = 1;
+	case 'l':
+		linenums = 1;
+		break;
+	case 'r':
+		registers = 1;
+		break;
+	case 's':
+		stacks = 1;
+		break;
+	}ARGEND
+	if(pid <= 0)
+		Usage();
+	if(functions+linenums+registers+stacks == 0)
+		histograms = 1;
+	if(!machbyname("amd64")) {
+		fprint(2, "prof: no amd64 support\n", pid);
+		exit(1);
+	}
+	if(argc > 0)
+		file = argv[0];
+	fd = open(file, 0);
+	if(fd < 0) {
+		fprint(2, "prof: can't open %s: %r\n", file);
+		exit(1);
+	}
+	map = attachproc(pid, &fhdr);
+	if(map == nil) {
+		fprint(2, "prof: can't attach to %d: %r\n", pid);
+		exit(1);
+	}
+	if(crackhdr(fd, &fhdr)) {
+		have_syms = syminit(fd, &fhdr);
+		if(!have_syms) {
+			fprint(2, "prof: no symbols for %s: %r\n", file);
+		}
+	} else {
+		fprint(2, "prof: crack header for %s: %r\n", file);
+		exit(1);
+	}
+	samples();
+	detachproc(map);
+	dumphistogram();
+	exit(0);
+}