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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * 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 vm_SPSProfiler_h
+#define vm_SPSProfiler_h
+
+#include "mozilla/DebugOnly.h"
+#include "mozilla/GuardObjects.h"
+
+#include <stddef.h>
+
+#include "jsscript.h"
+
+#include "js/ProfilingStack.h"
+#include "threading/ExclusiveData.h"
+#include "vm/MutexIDs.h"
+
+/*
+ * SPS Profiler integration with the JS Engine
+ * https://developer.mozilla.org/en/Performance/Profiling_with_the_Built-in_Profiler
+ *
+ * The SPS profiler (found in tools/profiler) is an implementation of a profiler
+ * which has the ability to walk the C++ stack as well as use instrumentation to
+ * gather information. When dealing with JS, however, SPS needs integration
+ * with the engine because otherwise it is very difficult to figure out what
+ * javascript is executing.
+ *
+ * The current method of integration with SPS is a form of instrumentation:
+ * every time a JS function is entered, a bit of information is pushed onto a
+ * stack that SPS owns and maintains. This information is then popped at the end
+ * of the JS function. SPS informs the JS engine of this stack at runtime, and
+ * it can by turned on/off dynamically.
+ *
+ * The SPS stack has three parameters: a base pointer, a size, and a maximum
+ * size. The stack is the ProfileEntry stack which will have information written
+ * to it. The size location is a pointer to an integer which represents the
+ * current size of the stack (number of valid frames). This size will be
+ * modified when JS functions are called. The maximum specified is the maximum
+ * capacity of the ProfileEntry stack.
+ *
+ * Throughout execution, the size of the stack recorded in memory may exceed the
+ * maximum. The JS engine will not write any information past the maximum limit,
+ * but it will still maintain the size of the stack. SPS code is aware of this
+ * and iterates the stack accordingly.
+ *
+ * There is some information pushed on the SPS stack for every JS function that
+ * is entered. First is a char* pointer of a description of what function was
+ * entered. Currently this string is of the form "function (file:line)" if
+ * there's a function name, or just "file:line" if there's no function name
+ * available. The other bit of information is the relevant C++ (native) stack
+ * pointer. This stack pointer is what enables the interleaving of the C++ and
+ * the JS stack. Finally, throughout execution of the function, some extra
+ * information may be updated on the ProfileEntry structure.
+ *
+ * = Profile Strings
+ *
+ * The profile strings' allocations and deallocation must be carefully
+ * maintained, and ideally at a very low overhead cost. For this reason, the JS
+ * engine maintains a mapping of all known profile strings. These strings are
+ * keyed in lookup by a JSScript*, but are serialized with a JSFunction*,
+ * JSScript* pair. A JSScript will destroy its corresponding profile string when
+ * the script is finalized.
+ *
+ * For this reason, a char* pointer pushed on the SPS stack is valid only while
+ * it is on the SPS stack. SPS uses sampling to read off information from this
+ * instrumented stack, and it therefore copies the string byte for byte when a
+ * JS function is encountered during sampling.
+ *
+ * = Native Stack Pointer
+ *
+ * The actual value pushed as the native pointer is nullptr for most JS
+ * functions. The reason for this is that there's actually very little
+ * correlation between the JS stack and the C++ stack because many JS functions
+ * all run in the same C++ frame, or can even go backwards in C++ when going
+ * from the JIT back to the interpreter.
+ *
+ * To alleviate this problem, all JS functions push nullptr as their "native
+ * stack pointer" to indicate that it's a JS function call. The function
+ * RunScript(), however, pushes an actual C++ stack pointer onto the SPS stack.
+ * This way when interleaving C++ and JS, if SPS sees a nullptr native stack
+ * pointer on the SPS stack, it looks backwards for the first non-nullptr
+ * pointer and uses that for all subsequent nullptr native stack pointers.
+ *
+ * = Line Numbers
+ *
+ * One goal of sampling is to get both a backtrace of the JS stack, but also
+ * know where within each function on the stack execution currently is. For
+ * this, each ProfileEntry has a 'pc' field to tell where its execution
+ * currently is. This field is updated whenever a call is made to another JS
+ * function, and for the JIT it is also updated whenever the JIT is left.
+ *
+ * This field is in a union with a uint32_t 'line' so that C++ can make use of
+ * the field as well. It was observed that tracking 'line' via PCToLineNumber in
+ * JS was far too expensive, so that is why the pc instead of the translated
+ * line number is stored.
+ *
+ * As an invariant, if the pc is nullptr, then the JIT is currently executing
+ * generated code. Otherwise execution is in another JS function or in C++. With
+ * this in place, only the top entry of the stack can ever have nullptr as its
+ * pc. Additionally with this invariant, it is possible to maintain mappings of
+ * JIT code to pc which can be accessed safely because they will only be
+ * accessed from a signal handler when the JIT code is executing.
+ */
+
+namespace js {
+
+// The `ProfileStringMap` weakly holds its `JSScript*` keys and owns its string
+// values. Entries are removed when the `JSScript` is finalized; see
+// `SPSProfiler::onScriptFinalized`.
+using ProfileStringMap = HashMap<JSScript*,
+                                 UniqueChars,
+                                 DefaultHasher<JSScript*>,
+                                 SystemAllocPolicy>;
+
+class AutoSPSEntry;
+class SPSEntryMarker;
+class SPSBaselineOSRMarker;
+
+class SPSProfiler
+{
+    friend class AutoSPSEntry;
+    friend class SPSEntryMarker;
+    friend class SPSBaselineOSRMarker;
+
+    JSRuntime*           rt;
+    ExclusiveData<ProfileStringMap> strings;
+    ProfileEntry*        stack_;
+    uint32_t*            size_;
+    uint32_t             max_;
+    bool                 slowAssertions;
+    uint32_t             enabled_;
+    void                (*eventMarker_)(const char*);
+
+    UniqueChars allocProfileString(JSScript* script, JSFunction* function);
+    void push(const char* string, void* sp, JSScript* script, jsbytecode* pc, bool copy,
+              ProfileEntry::Category category = ProfileEntry::Category::JS);
+    void pop();
+
+  public:
+    explicit SPSProfiler(JSRuntime* rt);
+
+    bool init();
+
+    uint32_t** addressOfSizePointer() {
+        return &size_;
+    }
+
+    uint32_t* addressOfMaxSize() {
+        return &max_;
+    }
+
+    ProfileEntry** addressOfStack() {
+        return &stack_;
+    }
+
+    uint32_t* sizePointer() { return size_; }
+    uint32_t maxSize() { return max_; }
+    uint32_t size() { MOZ_ASSERT(installed()); return *size_; }
+    ProfileEntry* stack() { return stack_; }
+
+    /* management of whether instrumentation is on or off */
+    bool enabled() { MOZ_ASSERT_IF(enabled_, installed()); return enabled_; }
+    bool installed() { return stack_ != nullptr && size_ != nullptr; }
+    void enable(bool enabled);
+    void enableSlowAssertions(bool enabled) { slowAssertions = enabled; }
+    bool slowAssertionsEnabled() { return slowAssertions; }
+
+    /*
+     * Functions which are the actual instrumentation to track run information
+     *
+     *   - enter: a function has started to execute
+     *   - updatePC: updates the pc information about where a function
+     *               is currently executing
+     *   - exit: this function has ceased execution, and no further
+     *           entries/exits will be made
+     */
+    bool enter(JSContext* cx, JSScript* script, JSFunction* maybeFun);
+    void exit(JSScript* script, JSFunction* maybeFun);
+    void updatePC(JSScript* script, jsbytecode* pc) {
+        if (enabled() && *size_ - 1 < max_) {
+            MOZ_ASSERT(*size_ > 0);
+            MOZ_ASSERT(stack_[*size_ - 1].rawScript() == script);
+            stack_[*size_ - 1].setPC(pc);
+        }
+    }
+
+    /* Enter wasm code */
+    void beginPseudoJS(const char* string, void* sp);
+    void endPseudoJS() { pop(); }
+
+    jsbytecode* ipToPC(JSScript* script, size_t ip) { return nullptr; }
+
+    void setProfilingStack(ProfileEntry* stack, uint32_t* size, uint32_t max);
+    void setEventMarker(void (*fn)(const char*));
+    const char* profileString(JSScript* script, JSFunction* maybeFun);
+    void onScriptFinalized(JSScript* script);
+
+    void markEvent(const char* event);
+
+    /* meant to be used for testing, not recommended to call in normal code */
+    size_t stringsCount();
+    void stringsReset();
+
+    uint32_t* addressOfEnabled() {
+        return &enabled_;
+    }
+
+    void trace(JSTracer* trc);
+    void fixupStringsMapAfterMovingGC();
+#ifdef JSGC_HASH_TABLE_CHECKS
+    void checkStringsMapAfterMovingGC();
+#endif
+};
+
+/*
+ * This class is used to suppress profiler sampling during
+ * critical sections where stack state is not valid.
+ */
+class MOZ_RAII AutoSuppressProfilerSampling
+{
+  public:
+    explicit AutoSuppressProfilerSampling(JSContext* cx MOZ_GUARD_OBJECT_NOTIFIER_PARAM);
+    explicit AutoSuppressProfilerSampling(JSRuntime* rt MOZ_GUARD_OBJECT_NOTIFIER_PARAM);
+
+    ~AutoSuppressProfilerSampling();
+
+  private:
+    JSRuntime* rt_;
+    bool previouslyEnabled_;
+    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
+};
+
+inline size_t
+SPSProfiler::stringsCount()
+{
+    return strings.lock()->count();
+}
+
+inline void
+SPSProfiler::stringsReset()
+{
+    strings.lock()->clear();
+}
+
+/*
+ * This class is used in RunScript() to push the marker onto the sampling stack
+ * that we're about to enter JS function calls. This is the only time in which a
+ * valid stack pointer is pushed to the sampling stack.
+ */
+class MOZ_RAII SPSEntryMarker
+{
+  public:
+    explicit SPSEntryMarker(JSRuntime* rt,
+                            JSScript* script
+                            MOZ_GUARD_OBJECT_NOTIFIER_PARAM);
+    ~SPSEntryMarker();
+
+  private:
+    SPSProfiler* profiler;
+    mozilla::DebugOnly<uint32_t> size_before;
+    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
+};
+
+/*
+ * RAII class to automatically add SPS psuedo frame entries.
+ *
+ * NB: The `label` string must be statically allocated.
+ */
+class MOZ_NONHEAP_CLASS AutoSPSEntry
+{
+  public:
+    explicit AutoSPSEntry(JSRuntime* rt, const char* label,
+                          ProfileEntry::Category category = ProfileEntry::Category::JS
+                          MOZ_GUARD_OBJECT_NOTIFIER_PARAM);
+    ~AutoSPSEntry();
+
+  private:
+    SPSProfiler* profiler_;
+    mozilla::DebugOnly<uint32_t> sizeBefore_;
+    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
+};
+
+/*
+ * This class is used in the interpreter to bound regions where the baseline JIT
+ * being entered via OSR.  It marks the current top pseudostack entry as
+ * OSR-ed
+ */
+class MOZ_RAII SPSBaselineOSRMarker
+{
+  public:
+    explicit SPSBaselineOSRMarker(JSRuntime* rt, bool hasSPSFrame
+                                  MOZ_GUARD_OBJECT_NOTIFIER_PARAM);
+    ~SPSBaselineOSRMarker();
+
+  private:
+    SPSProfiler* profiler;
+    mozilla::DebugOnly<uint32_t> size_before;
+    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
+};
+
+/*
+ * SPS is the profiling backend used by the JS engine to enable time profiling.
+ * More information can be found in vm/SPSProfiler.{h,cpp}. This class manages
+ * the instrumentation portion of the profiling for JIT code.
+ *
+ * The instrumentation tracks entry into functions, leaving those functions via
+ * a function call, reentering the functions from a function call, and exiting
+ * the functions from returning. This class also handles inline frames and
+ * manages the instrumentation which needs to be attached to them as well.
+ *
+ * The basic methods which emit instrumentation are at the end of this class,
+ * and the management functions are all described in the middle.
+ */
+template<class Assembler, class Register>
+class SPSInstrumentation
+{
+    SPSProfiler* profiler_; // Instrumentation location management
+
+  public:
+    /*
+     * Creates instrumentation which writes information out the the specified
+     * profiler's stack and constituent fields.
+     */
+    explicit SPSInstrumentation(SPSProfiler* profiler) : profiler_(profiler) {}
+
+    /* Small proxies around SPSProfiler */
+    bool enabled() { return profiler_ && profiler_->enabled(); }
+    SPSProfiler* profiler() { MOZ_ASSERT(enabled()); return profiler_; }
+    void disable() { profiler_ = nullptr; }
+};
+
+
+/* Get a pointer to the top-most profiling frame, given the exit frame pointer. */
+void* GetTopProfilingJitFrame(uint8_t* exitFramePtr);
+
+} /* namespace js */
+
+#endif /* vm_SPSProfiler_h */