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comparison: js/src/jit/AsmJS.h
js/src/jit/AsmJS.h
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| 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/. */ | |
| 6 | |
| 7 #ifndef jit_AsmJS_h | |
| 8 #define jit_AsmJS_h | |
| 9 | |
| 10 #include <stddef.h> | |
| 11 | |
| 12 #include "js/TypeDecls.h" | |
| 13 #include "vm/ObjectImpl.h" | |
| 14 | |
| 15 namespace js { | |
| 16 | |
| 17 class ExclusiveContext; | |
| 18 namespace frontend { | |
| 19 template <typename ParseHandler> struct Parser; | |
| 20 template <typename ParseHandler> struct ParseContext; | |
| 21 class FullParseHandler; | |
| 22 struct ParseNode; | |
| 23 } | |
| 24 | |
| 25 typedef frontend::Parser<frontend::FullParseHandler> AsmJSParser; | |
| 26 typedef frontend::ParseContext<frontend::FullParseHandler> AsmJSParseContext; | |
| 27 | |
| 28 // Takes over parsing of a function starting with "use asm". The return value | |
| 29 // indicates whether an error was reported which the caller should propagate. | |
| 30 // If no error was reported, the function may still fail to validate as asm.js. | |
| 31 // In this case, the parser.tokenStream has been advanced an indeterminate | |
| 32 // amount and the entire function should be reparsed from the beginning. | |
| 33 extern bool | |
| 34 CompileAsmJS(ExclusiveContext *cx, AsmJSParser &parser, frontend::ParseNode *stmtList, | |
| 35 bool *validated); | |
| 36 | |
| 37 // The assumed page size; dynamically checked in CompileAsmJS. | |
| 38 const size_t AsmJSPageSize = 4096; | |
| 39 | |
| 40 // The asm.js spec requires that the ArrayBuffer's byteLength be a multiple of 4096. | |
| 41 static const size_t AsmJSAllocationGranularity = 4096; | |
| 42 | |
| 43 #ifdef JS_CODEGEN_X64 | |
| 44 // On x64, the internal ArrayBuffer data array is inflated to 4GiB (only the | |
| 45 // byteLength portion of which is accessible) so that out-of-bounds accesses | |
| 46 // (made using a uint32 index) are guaranteed to raise a SIGSEGV. | |
| 47 static const size_t AsmJSBufferProtectedSize = 4 * 1024ULL * 1024ULL * 1024ULL; | |
| 48 | |
| 49 // To avoid dynamically checking bounds on each load/store, asm.js code relies | |
| 50 // on the SIGSEGV handler in AsmJSSignalHandlers.cpp. However, this only works | |
| 51 // if we can guarantee that *any* out-of-bounds access generates a fault. This | |
| 52 // isn't generally true since an out-of-bounds access could land on other | |
| 53 // Mozilla data. To overcome this on x64, we reserve an entire 4GB space, | |
| 54 // making only the range [0, byteLength) accessible, and use a 32-bit unsigned | |
| 55 // index into this space. (x86 and ARM require different tricks.) | |
| 56 // | |
| 57 // One complication is that we need to put an ObjectElements struct immediately | |
| 58 // before the data array (as required by the general JSObject data structure). | |
| 59 // Thus, we must stick a page before the elements to hold ObjectElements. | |
| 60 // | |
| 61 // |<------------------------------ 4GB + 1 pages --------------------->| | |
| 62 // |<--- sizeof --->|<------------------- 4GB ----------------->| | |
| 63 // | |
| 64 // | waste | ObjectElements | data array | inaccessible reserved memory | | |
| 65 // ^ ^ ^ | |
| 66 // | \ / | |
| 67 // obj->elements required to be page boundaries | |
| 68 // | |
| 69 static const size_t AsmJSMappedSize = AsmJSPageSize + AsmJSBufferProtectedSize; | |
| 70 #endif // JS_CODEGEN_X64 | |
| 71 | |
| 72 #ifdef JS_ION | |
| 73 | |
| 74 // Return whether asm.js optimization is inhibitted by the platform or | |
| 75 // dynamically disabled: | |
| 76 extern bool | |
| 77 IsAsmJSCompilationAvailable(JSContext *cx, unsigned argc, JS::Value *vp); | |
| 78 | |
| 79 #else // JS_ION | |
| 80 | |
| 81 inline bool | |
| 82 IsAsmJSCompilationAvailable(JSContext *cx, unsigned argc, Value *vp) | |
| 83 { | |
| 84 CallArgs args = CallArgsFromVp(argc, vp); | |
| 85 args.rval().set(BooleanValue(false)); | |
| 86 return true; | |
| 87 } | |
| 88 | |
| 89 #endif // JS_ION | |
| 90 | |
| 91 // The Asm.js heap length is constrained by the x64 backend heap access scheme | |
| 92 // to be a multiple of the page size which is 4096 bytes, and also constrained | |
| 93 // by the limits of ARM backends 'cmp immediate' instruction which supports a | |
| 94 // complex range for the immediate argument. | |
| 95 // | |
| 96 // ARMv7 mode supports the following immediate constants, and the Thumb T2 | |
| 97 // instruction encoding also supports the subset of immediate constants used. | |
| 98 // abcdefgh 00000000 00000000 00000000 | |
| 99 // 00abcdef gh000000 00000000 00000000 | |
| 100 // 0000abcd efgh0000 00000000 00000000 | |
| 101 // 000000ab cdefgh00 00000000 00000000 | |
| 102 // 00000000 abcdefgh 00000000 00000000 | |
| 103 // 00000000 00abcdef gh000000 00000000 | |
| 104 // 00000000 0000abcd efgh0000 00000000 | |
| 105 // ... | |
| 106 // | |
| 107 // The 4096 page size constraint restricts the length to: | |
| 108 // xxxxxxxx xxxxxxxx xxxx0000 00000000 | |
| 109 // | |
| 110 // Intersecting all the above constraints gives: | |
| 111 // Heap length 0x40000000 to 0xff000000 quanta 0x01000000 | |
| 112 // Heap length 0x10000000 to 0x3fc00000 quanta 0x00400000 | |
| 113 // Heap length 0x04000000 to 0x0ff00000 quanta 0x00100000 | |
| 114 // Heap length 0x01000000 to 0x03fc0000 quanta 0x00040000 | |
| 115 // Heap length 0x00400000 to 0x00ff0000 quanta 0x00010000 | |
| 116 // Heap length 0x00100000 to 0x003fc000 quanta 0x00004000 | |
| 117 // Heap length 0x00001000 to 0x000ff000 quanta 0x00001000 | |
| 118 // | |
| 119 inline uint32_t | |
| 120 RoundUpToNextValidAsmJSHeapLength(uint32_t length) | |
| 121 { | |
| 122 if (length < 0x00001000u) // Minimum length is the pages size of 4096. | |
| 123 return 0x1000u; | |
| 124 if (length < 0x00100000u) // < 1M quanta 4K | |
| 125 return (length + 0x00000fff) & ~0x00000fff; | |
| 126 if (length < 0x00400000u) // < 4M quanta 16K | |
| 127 return (length + 0x00003fff) & ~0x00003fff; | |
| 128 if (length < 0x01000000u) // < 16M quanta 64K | |
| 129 return (length + 0x0000ffff) & ~0x0000ffff; | |
| 130 if (length < 0x04000000u) // < 64M quanta 256K | |
| 131 return (length + 0x0003ffff) & ~0x0003ffff; | |
| 132 if (length < 0x10000000u) // < 256M quanta 1M | |
| 133 return (length + 0x000fffff) & ~0x000fffff; | |
| 134 if (length < 0x40000000u) // < 1024M quanta 4M | |
| 135 return (length + 0x003fffff) & ~0x003fffff; | |
| 136 // < 4096M quanta 16M. Note zero is returned if over 0xff000000 but such | |
| 137 // lengths are not currently valid. | |
| 138 JS_ASSERT(length <= 0xff000000); | |
| 139 return (length + 0x00ffffff) & ~0x00ffffff; | |
| 140 } | |
| 141 | |
| 142 inline bool | |
| 143 IsValidAsmJSHeapLength(uint32_t length) | |
| 144 { | |
| 145 if (length < AsmJSAllocationGranularity) | |
| 146 return false; | |
| 147 if (length <= 0x00100000u) | |
| 148 return (length & 0x00000fff) == 0; | |
| 149 if (length <= 0x00400000u) | |
| 150 return (length & 0x00003fff) == 0; | |
| 151 if (length <= 0x01000000u) | |
| 152 return (length & 0x0000ffff) == 0; | |
| 153 if (length <= 0x04000000u) | |
| 154 return (length & 0x0003ffff) == 0; | |
| 155 if (length <= 0x10000000u) | |
| 156 return (length & 0x000fffff) == 0; | |
| 157 if (length <= 0x40000000u) | |
| 158 return (length & 0x003fffff) == 0; | |
| 159 if (length <= 0xff000000u) | |
| 160 return (length & 0x00ffffff) == 0; | |
| 161 return false; | |
| 162 } | |
| 163 | |
| 164 } // namespace js | |
| 165 | |
| 166 #endif // jit_AsmJS_h |
