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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 "jslock.h"

 #include "jsscript.h"

 #include "js/ProfilingStack.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 {

 class ProfileEntry;

 typedef HashMap<JSScript*, const char*, DefaultHasher<JSScript*>, SystemAllocPolicy>

         ProfileStringMap;

 class SPSEntryMarker;

 class SPSProfiler

 {

     friend class SPSEntryMarker;

     JSRuntime            *rt;

     ProfileStringMap     strings;

     ProfileEntry         *stack_;

     uint32_t             *size_;

     uint32_t             max_;

     bool                 slowAssertions;

     uint32_t             enabled_;

     PRLock               *lock_;

     void                (*eventMarker_)(const char *);

     const char *allocProfileString(JSScript *script, JSFunction *function);

     void push(const char *string, void *sp, JSScript *script, jsbytecode *pc);

     void pushNoCopy(const char *string, void *sp,

                     JSScript *script, jsbytecode *pc) {

         push(string, reinterpret_cast<void*>(

             reinterpret_cast<uintptr_t>(sp) | ProfileEntry::NoCopyBit),

             script, pc);

     }

     void pop();

   public:

     SPSProfiler(JSRuntime *rt);

     ~SPSProfiler();

     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_; }

     ProfileEntry *stack() { return stack_; }

     /* management of whether instrumentation is on or off */

     bool enabled() { JS_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(JSScript *script, JSFunction *maybeFun);

     void exit(JSScript *script, JSFunction *maybeFun);

     void updatePC(JSScript *script, jsbytecode *pc) {

         if (enabled() && *size_ - 1 < max_) {

             JS_ASSERT(*size_ > 0);

             JS_ASSERT(stack_[*size_ - 1].script() == script);

             stack_[*size_ - 1].setPC(pc);

         }

     }

     /* Enter a C++ function. */

     void enterNative(const char *string, void *sp);

     void exitNative() { 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_;

     }

 };

 /*

  * This class is used to make sure the strings table

  * is only accessed on one thread at a time.

  */

 class AutoSPSLock

 {

   public:

 #ifdef JS_THREADSAFE

     AutoSPSLock(PRLock *lock)

     {

         MOZ_ASSERT(lock, "Parameter should not be null!");

         lock_ = lock;

         PR_Lock(lock);

     }

     ~AutoSPSLock() { PR_Unlock(lock_); }

 #else

     AutoSPSLock(PRLock *) {}

 #endif

   private:

     PRLock *lock_;

 };

 inline size_t

 SPSProfiler::stringsCount()

 {

     AutoSPSLock lock(lock_);

     return strings.count();

 }

 inline void

 SPSProfiler::stringsReset()

 {

     AutoSPSLock lock(lock_);

     strings.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 SPSEntryMarker

 {

   public:

     SPSEntryMarker(JSRuntime *rt

                    MOZ_GUARD_OBJECT_NOTIFIER_PARAM);

     ~SPSEntryMarker();

   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

 {

     /* Because of inline frames, this is a nested structure in a vector */

     struct FrameState {

         JSScript *script; // script for this frame, nullptr if not pushed yet

         jsbytecode *pc;   // pc at which this frame was left for entry into a callee

         bool skipNext;    // should the next call to reenter be skipped?

         int  left;        // number of leave() calls made without a matching reenter()

     };

     SPSProfiler *profiler_; // Instrumentation location management

     Vector<FrameState, 1, SystemAllocPolicy> frames;

     FrameState *frame;

     static void clearFrame(FrameState *frame) {

         frame->script = nullptr;

         frame->pc = nullptr;

         frame->skipNext = false;

         frame->left = 0;

     }

   public:

     /*

      * Creates instrumentation which writes information out the the specified

      * profiler's stack and constituent fields.

      */

     SPSInstrumentation(SPSProfiler *profiler)

       : profiler_(profiler), frame(nullptr)

     {

         enterInlineFrame(nullptr);

     }

     /* Small proxies around SPSProfiler */

     bool enabled() { return profiler_ && profiler_->enabled(); }

     SPSProfiler *profiler() { JS_ASSERT(enabled()); return profiler_; }

     void disable() { profiler_ = nullptr; }

     /* Signals an inline function returned, reverting to the previous state */

     void leaveInlineFrame() {

         if (!enabled())

             return;

         JS_ASSERT(frame->left == 0);

         JS_ASSERT(frame->script != nullptr);

         frames.shrinkBy(1);

         JS_ASSERT(frames.length() > 0);

         frame = &frames[frames.length() - 1];

     }

     /* Saves the current state and assumes a fresh one for the inline function */

     bool enterInlineFrame(jsbytecode *callerPC) {

         if (!enabled())

             return true;

         JS_ASSERT_IF(frames.empty(), callerPC == nullptr);

         JS_ASSERT_IF(frame != nullptr, frame->script != nullptr);

         JS_ASSERT_IF(frame != nullptr, frame->left == 1);

         if (!frames.empty()) {

             JS_ASSERT(frame == &frames[frames.length() - 1]);

             frame->pc = callerPC;

         }

         if (!frames.growBy(1))

             return false;

         frame = &frames[frames.length() - 1];

         clearFrame(frame);

         return true;

     }

     /* Prepares the instrumenter state for generating OOL code, by

      * setting up the frame state to seem as if there are exactly

      * two pushed frames: a frame for the top-level script, and

      * a frame for the OOL code being generated.  Any

      * vm-calls from the OOL code will "leave" the OOL frame and

      * return back to it.

      */

     bool prepareForOOL() {

         if (!enabled())

             return true;

         JS_ASSERT(!frames.empty());

         if (frames.length() >= 2) {

             frames.shrinkBy(frames.length() - 2);

         } else { // frames.length() == 1

             if (!frames.growBy(1))

                 return false;

         }

         frames[0].pc = frames[0].script->code();

         frame = &frames[1];

         clearFrame(frame);

         return true;

     }

     void finishOOL() {

         if (!enabled())

             return;

         JS_ASSERT(!frames.empty());

         frames.shrinkBy(frames.length() - 1);

     }

     /* Number of inline frames currently active (doesn't include original one) */

     unsigned inliningDepth() {

         return frames.length() - 1;

     }

     /*

      * When debugging or with slow assertions, sometimes a C++ method will be

      * invoked to perform the pop operation from the SPS stack. When we leave

      * JIT code, we need to record the current PC, but upon reentering JIT

      * code, no update back to nullptr should happen. This method exists to

      * flag this behavior. The next leave() will emit instrumentation, but the

      * following reenter() will be a no-op.

      */

     void skipNextReenter() {

         /* If we've left the frame, the reenter will be skipped anyway */

         if (!enabled() || frame->left != 0)

             return;

         JS_ASSERT(frame->script);

         JS_ASSERT(!frame->skipNext);

         frame->skipNext = true;

     }

     /*

      * In some cases, a frame needs to be flagged as having been pushed, but no

      * instrumentation should be emitted. This updates internal state to flag

      * that further instrumentation should actually be emitted.

      */

     void setPushed(JSScript *script) {

         if (!enabled())

             return;

         JS_ASSERT(frame->left == 0);

         frame->script = script;

     }

     /*

      * Flags entry into a JS function for the first time. Before this is called,

      * no instrumentation is emitted, but after this instrumentation is emitted.

      */

     bool push(JSScript *script, Assembler &masm, Register scratch, bool inlinedFunction = false) {

         if (!enabled())

             return true;

 #ifdef JS_ION

         if (!inlinedFunction || jit::js_JitOptions.profileInlineFrames) {

 #endif

             const char *string = profiler_->profileString(script, script->functionNonDelazifying());

             if (string == nullptr)

                 return false;

             masm.spsPushFrame(profiler_, string, script, scratch);

 #ifdef JS_ION

         }

 #endif

         setPushed(script);

         return true;

     }

     /*

      * Signifies that C++ performed the push() for this function. C++ always

      * sets the current PC to something non-null, however, so as soon as JIT

      * code is reentered this updates the current pc to nullptr.

      */

     void pushManual(JSScript *script, Assembler &masm, Register scratch,

                     bool inlinedFunction = false)

     {

         if (!enabled())

             return;

 #ifdef JS_ION

         if (!inlinedFunction || jit::js_JitOptions.profileInlineFrames)

 #endif

             masm.spsUpdatePCIdx(profiler_, ProfileEntry::NullPCIndex, scratch);

         setPushed(script);

     }

     /*

      * Signals that the current function is leaving for a function call. This

      * can happen both on JS function calls and also calls to C++. This

      * internally manages how many leave() calls have been seen, and only the

      * first leave() emits instrumentation. Similarly, only the last

      * corresponding reenter() actually emits instrumentation.

      */

     void leave(jsbytecode *pc, Assembler &masm, Register scratch, bool inlinedFunction = false) {

         if (enabled() && frame->script && frame->left++ == 0) {

             jsbytecode *updatePC = pc;

             JSScript *script = frame->script;

 #ifdef JS_ION

             if (!inlinedFunction) {

                 // We may be leaving an inlined frame for entry into a C++

                 // frame.  If profileInlineFrames is turned off, use the top

                 // script's pc offset instead of the innermost script's.

                 if (!jit::js_JitOptions.profileInlineFrames && inliningDepth() > 0) {

                     JS_ASSERT(frames[0].pc);

                     updatePC = frames[0].pc;

                     script = frames[0].script;

                 }

             }

 #endif

 #ifdef JS_ION

             if (!inlinedFunction || jit::js_JitOptions.profileInlineFrames)

 #endif

                 masm.spsUpdatePCIdx(profiler_, script->pcToOffset(updatePC), scratch);

         }

     }

     /*

      * Flags that the leaving of the current function has returned. This tracks

      * state with leave() to only emit instrumentation at proper times.

      */

     void reenter(Assembler &masm, Register scratch, bool inlinedFunction = false) {

         if (!enabled() || !frame->script || frame->left-- != 1)

             return;

         if (frame->skipNext) {

             frame->skipNext = false;

         } else {

 #ifdef JS_ION

              if (!inlinedFunction || jit::js_JitOptions.profileInlineFrames)

 #endif

                  masm.spsUpdatePCIdx(profiler_, ProfileEntry::NullPCIndex, scratch);

         }

     }

     /*

      * Signifies exiting a JS frame, popping the SPS entry. Because there can be

      * multiple return sites of a function, this does not cease instrumentation

      * emission.

      */

     void pop(Assembler &masm, Register scratch, bool inlinedFunction = false) {

         if (enabled()) {

             JS_ASSERT(frame->left == 0);

             JS_ASSERT(frame->script);

 #ifdef JS_ION

             if (!inlinedFunction || jit::js_JitOptions.profileInlineFrames)

 #endif

                 masm.spsPopFrame(profiler_, scratch);

         }

     }

 };

 } /* namespace js */

 #endif /* vm_SPSProfiler_h */