The Tor Browser: js/src/jit/PcScriptCache.h@6474c204b198

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

     1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-

     2  * vim: set ts=8 sts=4 et sw=4 tw=99:

     3  * This Source Code Form is subject to the terms of the Mozilla Public

     4  * License, v. 2.0. If a copy of the MPL was not distributed with this

     5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

     7 #ifndef jit_PcScriptCache_h

     8 #define jit_PcScriptCache_h

    10 // Defines a fixed-size hash table solely for the purpose of caching jit::GetPcScript().

    11 // One cache is attached to each JSRuntime; it functions as if cleared on GC.

    13 struct JSRuntime;

    15 namespace js {

    16 namespace jit {

    18 struct PcScriptCacheEntry

    19 {

    20     uint8_t *returnAddress; // Key into the hash table.

    21     jsbytecode *pc;         // Cached PC.

    22     JSScript *script;       // Cached script.

    23 };

    25 struct PcScriptCache

    26 {

    27     static const uint32_t Length = 73;

    29     // GC number at the time the cache was filled or created.

    30     // Storing and checking against this number allows us to not bother

    31     // clearing this cache on every GC -- only when actually necessary.

    32     uint64_t gcNumber;

    34     // List of cache entries.

    35     mozilla::Array<PcScriptCacheEntry, Length> entries;

    37     void clear(uint64_t gcNumber) {

    38         for (uint32_t i = 0; i < Length; i++)

    39             entries[i].returnAddress = nullptr;

    40         this->gcNumber = gcNumber;

    41     }

    43     // Get a value from the cache. May perform lazy allocation.

    44     bool get(JSRuntime *rt, uint32_t hash, uint8_t *addr,

    45              JSScript **scriptRes, jsbytecode **pcRes)

    46     {

    47         // If a GC occurred, lazily clear the cache now.

    48         if (gcNumber != rt->gcNumber) {

    49             clear(rt->gcNumber);

    50             return false;

    51         }

    53         if (entries[hash].returnAddress != addr)

    54             return false;

    56         *scriptRes = entries[hash].script;

    57         if (pcRes)

    58             *pcRes = entries[hash].pc;

    60         return true;

    61     }

    63     void add(uint32_t hash, uint8_t *addr, jsbytecode *pc, JSScript *script) {

    64         entries[hash].returnAddress = addr;

    65         entries[hash].pc = pc;

    66         entries[hash].script = script;

    67     }

    69     static uint32_t Hash(uint8_t *addr) {

    70         uint32_t key = (uint32_t)((uintptr_t)addr);

    71         return ((key >> 3) * 2654435761u) % Length;

    72     }

    73 };

    75 } // namespace jit

    76 } // namespace js

    78 #endif /* jit_PcScriptCache_h */

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