Add m-esr52 at 52.6.0

4 files changed, 799 insertions, 0 deletions

diff --git a/js/src/perf/jsperf.cpp b/js/src/perf/jsperf.cpp
new file mode 100644
index 000000000..ca2db4458
--- /dev/null
+++ b/js/src/perf/jsperf.cpp
@@ -0,0 +1,293 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "perf/jsperf.h"
+
+#include "jscntxt.h" /* for error messages */
+#include "jsobj.h" /* for unwrapping without a context */
+
+using namespace js;
+using JS::PerfMeasurement;
+
+// You cannot forward-declare a static object in C++, so instead
+// we have to forward-declare the helper function that refers to it.
+static PerfMeasurement* GetPM(JSContext* cx, JS::HandleValue value, const char* fname);
+
+// Property access
+
+#define GETTER(name)                                                    \
+    static bool                                                         \
+    pm_get_##name(JSContext* cx, unsigned argc, Value* vp)              \
+    {                                                                   \
+        CallArgs args = CallArgsFromVp(argc, vp);                       \
+        PerfMeasurement* p = GetPM(cx, args.thisv(), #name);            \
+        if (!p)                                                         \
+            return false;                                               \
+        args.rval().setNumber(double(p->name));                         \
+        return true;                                                    \
+    }
+
+GETTER(cpu_cycles)
+GETTER(instructions)
+GETTER(cache_references)
+GETTER(cache_misses)
+GETTER(branch_instructions)
+GETTER(branch_misses)
+GETTER(bus_cycles)
+GETTER(page_faults)
+GETTER(major_page_faults)
+GETTER(context_switches)
+GETTER(cpu_migrations)
+GETTER(eventsMeasured)
+
+#undef GETTER
+
+// Calls
+
+static bool
+pm_start(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    PerfMeasurement* p = GetPM(cx, args.thisv(), "start");
+    if (!p)
+        return false;
+
+    p->start();
+    args.rval().setUndefined();
+    return true;
+}
+
+static bool
+pm_stop(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    PerfMeasurement* p = GetPM(cx, args.thisv(), "stop");
+    if (!p)
+        return false;
+
+    p->stop();
+    args.rval().setUndefined();
+    return true;
+}
+
+static bool
+pm_reset(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    PerfMeasurement* p = GetPM(cx, args.thisv(), "reset");
+    if (!p)
+        return false;
+
+    p->reset();
+    args.rval().setUndefined();
+    return true;
+}
+
+static bool
+pm_canMeasureSomething(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    PerfMeasurement* p = GetPM(cx, args.thisv(), "canMeasureSomething");
+    if (!p)
+        return false;
+
+    args.rval().setBoolean(p->canMeasureSomething());
+    return true;
+}
+
+static const uint8_t PM_FATTRS = JSPROP_READONLY | JSPROP_PERMANENT;
+static const JSFunctionSpec pm_fns[] = {
+    JS_FN("start",               pm_start,               0, PM_FATTRS),
+    JS_FN("stop",                pm_stop,                0, PM_FATTRS),
+    JS_FN("reset",               pm_reset,               0, PM_FATTRS),
+    JS_FN("canMeasureSomething", pm_canMeasureSomething, 0, PM_FATTRS),
+    JS_FS_END
+};
+
+static const uint8_t PM_PATTRS =
+    JSPROP_ENUMERATE | JSPROP_PERMANENT;
+
+#define GETTER(name)                            \
+    JS_PSG(#name, pm_get_##name, PM_PATTRS)
+
+static const JSPropertySpec pm_props[] = {
+    GETTER(cpu_cycles),
+    GETTER(instructions),
+    GETTER(cache_references),
+    GETTER(cache_misses),
+    GETTER(branch_instructions),
+    GETTER(branch_misses),
+    GETTER(bus_cycles),
+    GETTER(page_faults),
+    GETTER(major_page_faults),
+    GETTER(context_switches),
+    GETTER(cpu_migrations),
+    GETTER(eventsMeasured),
+    JS_PS_END
+};
+
+#undef GETTER
+
+// If this were C++ these would be "static const" members.
+
+#define CONSTANT(name) { #name, PerfMeasurement::name }
+
+static const struct pm_const {
+    const char* name;
+    PerfMeasurement::EventMask value;
+} pm_consts[] = {
+    CONSTANT(CPU_CYCLES),
+    CONSTANT(INSTRUCTIONS),
+    CONSTANT(CACHE_REFERENCES),
+    CONSTANT(CACHE_MISSES),
+    CONSTANT(BRANCH_INSTRUCTIONS),
+    CONSTANT(BRANCH_MISSES),
+    CONSTANT(BUS_CYCLES),
+    CONSTANT(PAGE_FAULTS),
+    CONSTANT(MAJOR_PAGE_FAULTS),
+    CONSTANT(CONTEXT_SWITCHES),
+    CONSTANT(CPU_MIGRATIONS),
+    CONSTANT(ALL),
+    CONSTANT(NUM_MEASURABLE_EVENTS),
+    { 0, PerfMeasurement::EventMask(0) }
+};
+
+#undef CONSTANT
+
+static bool pm_construct(JSContext* cx, unsigned argc, Value* vp);
+static void pm_finalize(JSFreeOp* fop, JSObject* obj);
+
+static const JSClassOps pm_classOps = {
+    nullptr,
+    nullptr,
+    nullptr,
+    nullptr,
+    nullptr,
+    nullptr,
+    nullptr,
+    pm_finalize
+};
+
+static const JSClass pm_class = {
+    "PerfMeasurement",
+    JSCLASS_HAS_PRIVATE |
+    JSCLASS_FOREGROUND_FINALIZE,
+    &pm_classOps
+};
+
+// Constructor and destructor
+
+static bool
+pm_construct(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    uint32_t mask;
+    if (!args.hasDefined(0)) {
+        ReportMissingArg(cx, args.calleev(), 0);
+        return false;
+    }
+    if (!JS::ToUint32(cx, args[0], &mask))
+        return false;
+
+    JS::RootedObject obj(cx, JS_NewObjectForConstructor(cx, &pm_class, args));
+    if (!obj)
+        return false;
+
+    if (!JS_FreezeObject(cx, obj))
+        return false;
+
+    PerfMeasurement* p = cx->new_<PerfMeasurement>(PerfMeasurement::EventMask(mask));
+    if (!p) {
+        JS_ReportOutOfMemory(cx);
+        return false;
+    }
+
+    JS_SetPrivate(obj, p);
+    args.rval().setObject(*obj);
+    return true;
+}
+
+static void
+pm_finalize(JSFreeOp* fop, JSObject* obj)
+{
+    js::FreeOp::get(fop)->delete_(static_cast<PerfMeasurement*>(JS_GetPrivate(obj)));
+}
+
+// Helpers (declared above)
+
+static PerfMeasurement*
+GetPM(JSContext* cx, JS::HandleValue value, const char* fname)
+{
+    if (!value.isObject()) {
+        UniqueChars bytes = DecompileValueGenerator(cx, JSDVG_SEARCH_STACK, value, nullptr);
+        if (!bytes)
+            return nullptr;
+        JS_ReportErrorNumberLatin1(cx, GetErrorMessage, 0, JSMSG_NOT_NONNULL_OBJECT, bytes.get());
+        return nullptr;
+    }
+    RootedObject obj(cx, &value.toObject());
+    PerfMeasurement* p = (PerfMeasurement*)
+        JS_GetInstancePrivate(cx, obj, &pm_class, nullptr);
+    if (p)
+        return p;
+
+    // JS_GetInstancePrivate only sets an exception if its last argument
+    // is nonzero, so we have to do it by hand.
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, 0, JSMSG_INCOMPATIBLE_PROTO,
+                              pm_class.name, fname, JS_GetClass(obj)->name);
+    return nullptr;
+}
+
+namespace JS {
+
+JSObject*
+RegisterPerfMeasurement(JSContext* cx, HandleObject globalArg)
+{
+    static const uint8_t PM_CATTRS = JSPROP_ENUMERATE|JSPROP_READONLY|JSPROP_PERMANENT;
+
+    RootedObject global(cx, globalArg);
+    RootedObject prototype(cx);
+    prototype = JS_InitClass(cx, global, nullptr /* parent */,
+                             &pm_class, pm_construct, 1,
+                             pm_props, pm_fns, 0, 0);
+    if (!prototype)
+        return 0;
+
+    RootedObject ctor(cx);
+    ctor = JS_GetConstructor(cx, prototype);
+    if (!ctor)
+        return 0;
+
+    for (const pm_const* c = pm_consts; c->name; c++) {
+        if (!JS_DefineProperty(cx, ctor, c->name, c->value, PM_CATTRS,
+                               JS_STUBGETTER, JS_STUBSETTER))
+            return 0;
+    }
+
+    if (!JS_FreezeObject(cx, prototype) ||
+        !JS_FreezeObject(cx, ctor)) {
+        return 0;
+    }
+
+    return prototype;
+}
+
+PerfMeasurement*
+ExtractPerfMeasurement(const Value& wrapper)
+{
+    if (wrapper.isPrimitive())
+        return 0;
+
+    // This is what JS_GetInstancePrivate does internally.  We can't
+    // call JS_anything from here, because we don't have a JSContext.
+    JSObject* obj = wrapper.toObjectOrNull();
+    if (obj->getClass() != js::Valueify(&pm_class))
+        return 0;
+
+    return (PerfMeasurement*) obj->as<js::NativeObject>().getPrivate();
+}
+
+} // namespace JS
diff --git a/js/src/perf/jsperf.h b/js/src/perf/jsperf.h
new file mode 100644
index 000000000..b8f2909ad
--- /dev/null
+++ b/js/src/perf/jsperf.h
@@ -0,0 +1,133 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef perf_jsperf_h
+#define perf_jsperf_h
+
+#include "jstypes.h"
+
+#include "js/TypeDecls.h"
+#include "js/Utility.h"
+
+namespace JS {
+
+/*
+ * JS::PerfMeasurement is a generic way to access detailed performance
+ * measurement APIs provided by your operating system.  The details of
+ * exactly how this works and what can be measured are highly
+ * system-specific, but this interface is (one hopes) implementable
+ * on top of all of them.
+ *
+ * To use this API, create a PerfMeasurement object, passing its
+ * constructor a bitmask indicating which events you are interested
+ * in.  Thereafter, Start() zeroes all counters and starts timing;
+ * Stop() stops timing again; and the counters for the events you
+ * requested are available as data values after calling Stop().  The
+ * object may be reused for many measurements.
+ */
+class JS_FRIEND_API(PerfMeasurement)
+{
+  protected:
+    // Implementation-specific data, if any.
+    void* impl;
+
+  public:
+    /*
+     * Events that may be measured.  Taken directly from the list of
+     * "generalized hardware performance event types" in the Linux
+     * perf_event API, plus some of the "software events".
+     */
+    enum EventMask {
+        CPU_CYCLES          = 0x00000001,
+        INSTRUCTIONS        = 0x00000002,
+        CACHE_REFERENCES    = 0x00000004,
+        CACHE_MISSES        = 0x00000008,
+        BRANCH_INSTRUCTIONS = 0x00000010,
+        BRANCH_MISSES       = 0x00000020,
+        BUS_CYCLES          = 0x00000040,
+        PAGE_FAULTS         = 0x00000080,
+        MAJOR_PAGE_FAULTS   = 0x00000100,
+        CONTEXT_SWITCHES    = 0x00000200,
+        CPU_MIGRATIONS      = 0x00000400,
+
+        ALL                 = 0x000007ff,
+        NUM_MEASURABLE_EVENTS  = 11
+    };
+
+    /*
+     * Bitmask of events that will be measured when this object is
+     * active (between Start() and Stop()).  This may differ from the
+     * bitmask passed to the constructor if the platform does not
+     * support measuring all of the requested events.
+     */
+    const EventMask eventsMeasured;
+
+    /*
+     * Counters for each measurable event.
+     * Immediately after one of these objects is created, all of the
+     * counters for enabled events will be zero, and all of the
+     * counters for disabled events will be uint64_t(-1).
+     */
+    uint64_t cpu_cycles;
+    uint64_t instructions;
+    uint64_t cache_references;
+    uint64_t cache_misses;
+    uint64_t branch_instructions;
+    uint64_t branch_misses;
+    uint64_t bus_cycles;
+    uint64_t page_faults;
+    uint64_t major_page_faults;
+    uint64_t context_switches;
+    uint64_t cpu_migrations;
+
+    /*
+     * Prepare to measure the indicated set of events.  If not all of
+     * the requested events can be measured on the current platform,
+     * then the eventsMeasured bitmask will only include the subset of
+     * |toMeasure| corresponding to the events that can be measured.
+     */
+    explicit PerfMeasurement(EventMask toMeasure);
+
+    /* Done with this set of measurements, tear down OS-level state. */
+    ~PerfMeasurement();
+
+    /* Start a measurement cycle. */
+    void start();
+
+    /*
+     * End a measurement cycle, and for each enabled counter, add the
+     * number of measured events of that type to the appropriate
+     * visible variable.
+     */
+    void stop();
+
+    /* Reset all enabled counters to zero. */
+    void reset();
+
+    /*
+     * True if this platform supports measuring _something_, i.e. it's
+     * not using the stub implementation.
+     */
+    static bool canMeasureSomething();
+};
+
+/* Inject a Javascript wrapper around the above C++ class into the
+ * Javascript object passed as an argument (this will normally be a
+ * global object).  The JS-visible API is identical to the C++ API.
+ */
+extern JS_FRIEND_API(JSObject*)
+    RegisterPerfMeasurement(JSContext* cx, JS::HandleObject global);
+
+/*
+ * Given a Value which contains an instance of the aforementioned
+ * wrapper class, extract the C++ object.  Returns nullptr if the
+ * Value is not an instance of the wrapper.
+ */
+extern JS_FRIEND_API(PerfMeasurement*)
+    ExtractPerfMeasurement(const Value& wrapper);
+
+} // namespace JS
+
+#endif /* perf_jsperf_h */
diff --git a/js/src/perf/pm_linux.cpp b/js/src/perf/pm_linux.cpp
new file mode 100644
index 000000000..54ba0c363
--- /dev/null
+++ b/js/src/perf/pm_linux.cpp
@@ -0,0 +1,310 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* This variant of nsIPerfMeasurement uses the perf_event interface
+ * added in Linux 2.6.31.  We key compilation of this file off the
+ * existence of <linux/perf_event.h>.
+ */
+
+#include <errno.h>
+#include <linux/perf_event.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#include "perf/jsperf.h"
+
+using namespace js;
+
+// As of July 2010, this system call has not been added to the
+// C library, so we have to provide our own wrapper function.
+// If this code runs on a kernel that does not implement the
+// system call (2.6.30 or older) nothing unpredictable will
+// happen - it will just always fail and return -1.
+static int
+sys_perf_event_open(struct perf_event_attr* attr, pid_t pid, int cpu,
+                    int group_fd, unsigned long flags)
+{
+    return syscall(__NR_perf_event_open, attr, pid, cpu, group_fd, flags);
+}
+
+namespace {
+
+using JS::PerfMeasurement;
+typedef PerfMeasurement::EventMask EventMask;
+
+// Additional state required by this implementation.
+struct Impl
+{
+    // Each active counter corresponds to an open file descriptor.
+    int f_cpu_cycles;
+    int f_instructions;
+    int f_cache_references;
+    int f_cache_misses;
+    int f_branch_instructions;
+    int f_branch_misses;
+    int f_bus_cycles;
+    int f_page_faults;
+    int f_major_page_faults;
+    int f_context_switches;
+    int f_cpu_migrations;
+
+    // Counter group leader, for Start and Stop.
+    int group_leader;
+
+    // Whether counters are running.
+    bool running;
+
+    Impl();
+    ~Impl();
+
+    EventMask init(EventMask toMeasure);
+    void start();
+    void stop(PerfMeasurement* counters);
+};
+
+// Mapping from our event bitmask to codes passed into the kernel, and
+// to fields in the PerfMeasurement and PerfMeasurement::impl structures.
+static const struct
+{
+    EventMask bit;
+    uint32_t type;
+    uint32_t config;
+    uint64_t PerfMeasurement::* counter;
+    int Impl::* fd;
+} kSlots[PerfMeasurement::NUM_MEASURABLE_EVENTS] = {
+#define HW(mask, constant, fieldname)                                   \
+    { PerfMeasurement::mask, PERF_TYPE_HARDWARE, PERF_COUNT_HW_##constant, \
+      &PerfMeasurement::fieldname, &Impl::f_##fieldname }
+#define SW(mask, constant, fieldname)                                   \
+    { PerfMeasurement::mask, PERF_TYPE_SOFTWARE, PERF_COUNT_SW_##constant, \
+      &PerfMeasurement::fieldname, &Impl::f_##fieldname }
+
+    HW(CPU_CYCLES,          CPU_CYCLES,          cpu_cycles),
+    HW(INSTRUCTIONS,        INSTRUCTIONS,        instructions),
+    HW(CACHE_REFERENCES,    CACHE_REFERENCES,    cache_references),
+    HW(CACHE_MISSES,        CACHE_MISSES,        cache_misses),
+    HW(BRANCH_INSTRUCTIONS, BRANCH_INSTRUCTIONS, branch_instructions),
+    HW(BRANCH_MISSES,       BRANCH_MISSES,       branch_misses),
+    HW(BUS_CYCLES,          BUS_CYCLES,          bus_cycles),
+    SW(PAGE_FAULTS,         PAGE_FAULTS,         page_faults),
+    SW(MAJOR_PAGE_FAULTS,   PAGE_FAULTS_MAJ,     major_page_faults),
+    SW(CONTEXT_SWITCHES,    CONTEXT_SWITCHES,    context_switches),
+    SW(CPU_MIGRATIONS,      CPU_MIGRATIONS,      cpu_migrations),
+
+#undef HW
+#undef SW
+};
+
+Impl::Impl()
+  : f_cpu_cycles(-1),
+    f_instructions(-1),
+    f_cache_references(-1),
+    f_cache_misses(-1),
+    f_branch_instructions(-1),
+    f_branch_misses(-1),
+    f_bus_cycles(-1),
+    f_page_faults(-1),
+    f_major_page_faults(-1),
+    f_context_switches(-1),
+    f_cpu_migrations(-1),
+    group_leader(-1),
+    running(false)
+{
+}
+
+Impl::~Impl()
+{
+    // Close all active counter descriptors.  Take care to do the group
+    // leader last (this may not be necessary, but it's unclear what
+    // happens if you close the group leader out from under a group).
+    for (const auto& slot : kSlots) {
+        int fd = this->*(slot.fd);
+        if (fd != -1 && fd != group_leader)
+            close(fd);
+    }
+
+    if (group_leader != -1)
+        close(group_leader);
+}
+
+EventMask
+Impl::init(EventMask toMeasure)
+{
+    MOZ_ASSERT(group_leader == -1);
+    if (!toMeasure)
+        return EventMask(0);
+
+    EventMask measured = EventMask(0);
+    struct perf_event_attr attr;
+    for (const auto& slot : kSlots) {
+        if (!(toMeasure & slot.bit))
+            continue;
+
+        memset(&attr, 0, sizeof(attr));
+        attr.size = sizeof(attr);
+
+        // Set the type and config fields to indicate the counter we
+        // want to enable.  We want read format 0, and we're not using
+        // sampling, so leave those fields unset.
+        attr.type = slot.type;
+        attr.config = slot.config;
+
+        // If this will be the group leader it should start off
+        // disabled.  Otherwise it should start off enabled (but blocked
+        // on the group leader).
+        if (group_leader == -1)
+            attr.disabled = 1;
+
+        // The rest of the bit fields are really poorly documented.
+        // For instance, I have *no idea* whether we should be setting
+        // the inherit, inherit_stat, or task flags.  I'm pretty sure
+        // we do want to set mmap and comm, and not any of the ones I
+        // haven't mentioned.
+        attr.mmap = 1;
+        attr.comm = 1;
+
+        int fd = sys_perf_event_open(&attr,
+                                     0 /* trace self */,
+                                     -1 /* on any cpu */,
+                                     group_leader,
+                                     0 /* no flags presently defined */);
+        if (fd == -1)
+            continue;
+
+        measured = EventMask(measured | slot.bit);
+        this->*(slot.fd) = fd;
+        if (group_leader == -1)
+            group_leader = fd;
+    }
+    return measured;
+}
+
+void
+Impl::start()
+{
+    if (running || group_leader == -1)
+        return;
+
+    running = true;
+    ioctl(group_leader, PERF_EVENT_IOC_ENABLE, 0);
+}
+
+void
+Impl::stop(PerfMeasurement* counters)
+{
+    // This scratch buffer is to ensure that we have read all the
+    // available data, even if that's more than we expect.
+    unsigned char buf[1024];
+
+    if (!running || group_leader == -1)
+        return;
+
+    ioctl(group_leader, PERF_EVENT_IOC_DISABLE, 0);
+    running = false;
+
+    // read out and reset all the counter values
+    for (const auto& slot : kSlots) {
+        int fd = this->*(slot.fd);
+        if (fd == -1)
+            continue;
+
+        if (read(fd, buf, sizeof(buf)) == sizeof(uint64_t)) {
+            uint64_t cur;
+            memcpy(&cur, buf, sizeof(uint64_t));
+            counters->*(slot.counter) += cur;
+        }
+
+        // Reset the counter regardless of whether the read did what
+        // we expected.
+        ioctl(fd, PERF_EVENT_IOC_RESET, 0);
+    }
+}
+
+} // namespace
+
+
+namespace JS {
+
+#define initCtr(flag) ((eventsMeasured & flag) ? 0 : -1)
+
+PerfMeasurement::PerfMeasurement(PerfMeasurement::EventMask toMeasure)
+  : impl(js_new<Impl>()),
+    eventsMeasured(impl ? static_cast<Impl*>(impl)->init(toMeasure)
+                   : EventMask(0)),
+    cpu_cycles(initCtr(CPU_CYCLES)),
+    instructions(initCtr(INSTRUCTIONS)),
+    cache_references(initCtr(CACHE_REFERENCES)),
+    cache_misses(initCtr(CACHE_MISSES)),
+    branch_instructions(initCtr(BRANCH_INSTRUCTIONS)),
+    branch_misses(initCtr(BRANCH_MISSES)),
+    bus_cycles(initCtr(BUS_CYCLES)),
+    page_faults(initCtr(PAGE_FAULTS)),
+    major_page_faults(initCtr(MAJOR_PAGE_FAULTS)),
+    context_switches(initCtr(CONTEXT_SWITCHES)),
+    cpu_migrations(initCtr(CPU_MIGRATIONS))
+{
+}
+
+#undef initCtr
+
+PerfMeasurement::~PerfMeasurement()
+{
+    js_delete(static_cast<Impl*>(impl));
+}
+
+void
+PerfMeasurement::start()
+{
+    if (impl)
+        static_cast<Impl*>(impl)->start();
+}
+
+void
+PerfMeasurement::stop()
+{
+    if (impl)
+        static_cast<Impl*>(impl)->stop(this);
+}
+
+void
+PerfMeasurement::reset()
+{
+    for (const auto& slot : kSlots) {
+        if (eventsMeasured & slot.bit)
+            this->*(slot.counter) = 0;
+        else
+            this->*(slot.counter) = -1;
+    }
+}
+
+bool
+PerfMeasurement::canMeasureSomething()
+{
+    // Find out if the kernel implements the performance measurement
+    // API.  If it doesn't, syscall(__NR_perf_event_open, ...) is
+    // guaranteed to return -1 and set errno to ENOSYS.
+    //
+    // We set up input parameters that should provoke an EINVAL error
+    // from a kernel that does implement perf_event_open, but we can't
+    // be sure it will (newer kernels might add more event types), so
+    // we have to take care to close any valid fd it might return.
+
+    struct perf_event_attr attr;
+    memset(&attr, 0, sizeof(attr));
+    attr.size = sizeof(attr);
+    attr.type = PERF_TYPE_MAX;
+
+    int fd = sys_perf_event_open(&attr, 0, -1, -1, 0);
+    if (fd >= 0) {
+        close(fd);
+        return true;
+    } else {
+        return errno != ENOSYS;
+    }
+}
+
+} // namespace JS
diff --git a/js/src/perf/pm_stub.cpp b/js/src/perf/pm_stub.cpp
new file mode 100644
index 000000000..bb6910c73
--- /dev/null
+++ b/js/src/perf/pm_stub.cpp
@@ -0,0 +1,63 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "perf/jsperf.h"
+
+namespace JS {
+
+PerfMeasurement::PerfMeasurement(PerfMeasurement::EventMask)
+  : impl(0),
+    eventsMeasured(EventMask(0)),
+    cpu_cycles(-1),
+    instructions(-1),
+    cache_references(-1),
+    cache_misses(-1),
+    branch_instructions(-1),
+    branch_misses(-1),
+    bus_cycles(-1),
+    page_faults(-1),
+    major_page_faults(-1),
+    context_switches(-1),
+    cpu_migrations(-1)
+{
+}
+
+PerfMeasurement::~PerfMeasurement()
+{
+}
+
+void
+PerfMeasurement::start()
+{
+}
+
+void
+PerfMeasurement::stop()
+{
+}
+
+void
+PerfMeasurement::reset()
+{
+    cpu_cycles = -1;
+    instructions = -1;
+    cache_references = -1;
+    cache_misses = -1;
+    branch_instructions = -1;
+    branch_misses = -1;
+    bus_cycles = -1;
+    page_faults = -1;
+    major_page_faults = -1;
+    context_switches = -1;
+    cpu_migrations = -1;
+}
+
+bool
+PerfMeasurement::canMeasureSomething()
+{
+    return false;
+}
+
+} // namespace JS