michael@0: /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
michael@0:  * vim: set ts=8 sts=4 et sw=4 tw=99:
michael@0:  * This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #ifndef jit_AsmJS_h
michael@0: #define jit_AsmJS_h
michael@0: 
michael@0: #include <stddef.h>
michael@0: 
michael@0: #include "js/TypeDecls.h"
michael@0: #include "vm/ObjectImpl.h"
michael@0: 
michael@0: namespace js {
michael@0: 
michael@0: class ExclusiveContext;
michael@0: namespace frontend {
michael@0:     template <typename ParseHandler> struct Parser;
michael@0:     template <typename ParseHandler> struct ParseContext;
michael@0:     class FullParseHandler;
michael@0:     struct ParseNode;
michael@0: }
michael@0: 
michael@0: typedef frontend::Parser<frontend::FullParseHandler> AsmJSParser;
michael@0: typedef frontend::ParseContext<frontend::FullParseHandler> AsmJSParseContext;
michael@0: 
michael@0: // Takes over parsing of a function starting with "use asm". The return value
michael@0: // indicates whether an error was reported which the caller should propagate.
michael@0: // If no error was reported, the function may still fail to validate as asm.js.
michael@0: // In this case, the parser.tokenStream has been advanced an indeterminate
michael@0: // amount and the entire function should be reparsed from the beginning.
michael@0: extern bool
michael@0: CompileAsmJS(ExclusiveContext *cx, AsmJSParser &parser, frontend::ParseNode *stmtList,
michael@0:              bool *validated);
michael@0: 
michael@0: // The assumed page size; dynamically checked in CompileAsmJS.
michael@0: const size_t AsmJSPageSize = 4096;
michael@0: 
michael@0: // The asm.js spec requires that the ArrayBuffer's byteLength be a multiple of 4096.
michael@0: static const size_t AsmJSAllocationGranularity = 4096;
michael@0: 
michael@0: #ifdef JS_CODEGEN_X64
michael@0: // On x64, the internal ArrayBuffer data array is inflated to 4GiB (only the
michael@0: // byteLength portion of which is accessible) so that out-of-bounds accesses
michael@0: // (made using a uint32 index) are guaranteed to raise a SIGSEGV.
michael@0: static const size_t AsmJSBufferProtectedSize = 4 * 1024ULL * 1024ULL * 1024ULL;
michael@0: 
michael@0: // To avoid dynamically checking bounds on each load/store, asm.js code relies
michael@0: // on the SIGSEGV handler in AsmJSSignalHandlers.cpp. However, this only works
michael@0: // if we can guarantee that *any* out-of-bounds access generates a fault. This
michael@0: // isn't generally true since an out-of-bounds access could land on other
michael@0: // Mozilla data. To overcome this on x64, we reserve an entire 4GB space,
michael@0: // making only the range [0, byteLength) accessible, and use a 32-bit unsigned
michael@0: // index into this space. (x86 and ARM require different tricks.)
michael@0: //
michael@0: // One complication is that we need to put an ObjectElements struct immediately
michael@0: // before the data array (as required by the general JSObject data structure).
michael@0: // Thus, we must stick a page before the elements to hold ObjectElements.
michael@0: //
michael@0: //   |<------------------------------ 4GB + 1 pages --------------------->|
michael@0: //           |<--- sizeof --->|<------------------- 4GB ----------------->|
michael@0: //
michael@0: //   | waste | ObjectElements | data array | inaccessible reserved memory |
michael@0: //                            ^            ^                              ^
michael@0: //                            |            \                             /
michael@0: //                      obj->elements       required to be page boundaries
michael@0: //
michael@0: static const size_t AsmJSMappedSize = AsmJSPageSize + AsmJSBufferProtectedSize;
michael@0: #endif // JS_CODEGEN_X64
michael@0: 
michael@0: #ifdef JS_ION
michael@0: 
michael@0: // Return whether asm.js optimization is inhibitted by the platform or
michael@0: // dynamically disabled:
michael@0: extern bool
michael@0: IsAsmJSCompilationAvailable(JSContext *cx, unsigned argc, JS::Value *vp);
michael@0: 
michael@0: #else // JS_ION
michael@0: 
michael@0: inline bool
michael@0: IsAsmJSCompilationAvailable(JSContext *cx, unsigned argc, Value *vp)
michael@0: {
michael@0:     CallArgs args = CallArgsFromVp(argc, vp);
michael@0:     args.rval().set(BooleanValue(false));
michael@0:     return true;
michael@0: }
michael@0: 
michael@0: #endif // JS_ION
michael@0: 
michael@0: // The Asm.js heap length is constrained by the x64 backend heap access scheme
michael@0: // to be a multiple of the page size which is 4096 bytes, and also constrained
michael@0: // by the limits of ARM backends 'cmp immediate' instruction which supports a
michael@0: // complex range for the immediate argument.
michael@0: //
michael@0: // ARMv7 mode supports the following immediate constants, and the Thumb T2
michael@0: // instruction encoding also supports the subset of immediate constants used.
michael@0: //  abcdefgh 00000000 00000000 00000000
michael@0: //  00abcdef gh000000 00000000 00000000
michael@0: //  0000abcd efgh0000 00000000 00000000
michael@0: //  000000ab cdefgh00 00000000 00000000
michael@0: //  00000000 abcdefgh 00000000 00000000
michael@0: //  00000000 00abcdef gh000000 00000000
michael@0: //  00000000 0000abcd efgh0000 00000000
michael@0: //  ...
michael@0: //
michael@0: // The 4096 page size constraint restricts the length to:
michael@0: //  xxxxxxxx xxxxxxxx xxxx0000 00000000
michael@0: //
michael@0: // Intersecting all the above constraints gives:
michael@0: //  Heap length 0x40000000 to 0xff000000 quanta 0x01000000
michael@0: //  Heap length 0x10000000 to 0x3fc00000 quanta 0x00400000
michael@0: //  Heap length 0x04000000 to 0x0ff00000 quanta 0x00100000
michael@0: //  Heap length 0x01000000 to 0x03fc0000 quanta 0x00040000
michael@0: //  Heap length 0x00400000 to 0x00ff0000 quanta 0x00010000
michael@0: //  Heap length 0x00100000 to 0x003fc000 quanta 0x00004000
michael@0: //  Heap length 0x00001000 to 0x000ff000 quanta 0x00001000
michael@0: //
michael@0: inline uint32_t
michael@0: RoundUpToNextValidAsmJSHeapLength(uint32_t length)
michael@0: {
michael@0:     if (length < 0x00001000u) // Minimum length is the pages size of 4096.
michael@0:         return 0x1000u;
michael@0:     if (length < 0x00100000u) // < 1M quanta 4K
michael@0:         return (length + 0x00000fff) & ~0x00000fff;
michael@0:     if (length < 0x00400000u) // < 4M quanta 16K
michael@0:         return (length + 0x00003fff) & ~0x00003fff;
michael@0:     if (length < 0x01000000u) // < 16M quanta 64K
michael@0:         return (length + 0x0000ffff) & ~0x0000ffff;
michael@0:     if (length < 0x04000000u) // < 64M quanta 256K
michael@0:         return (length + 0x0003ffff) & ~0x0003ffff;
michael@0:     if (length < 0x10000000u) // < 256M quanta 1M
michael@0:         return (length + 0x000fffff) & ~0x000fffff;
michael@0:     if (length < 0x40000000u) // < 1024M quanta 4M
michael@0:         return (length + 0x003fffff) & ~0x003fffff;
michael@0:     // < 4096M quanta 16M.  Note zero is returned if over 0xff000000 but such
michael@0:     // lengths are not currently valid.
michael@0:     JS_ASSERT(length <= 0xff000000);
michael@0:     return (length + 0x00ffffff) & ~0x00ffffff;
michael@0: }
michael@0: 
michael@0: inline bool
michael@0: IsValidAsmJSHeapLength(uint32_t length)
michael@0: {
michael@0:     if (length <  AsmJSAllocationGranularity)
michael@0:         return false;
michael@0:     if (length <= 0x00100000u)
michael@0:         return (length & 0x00000fff) == 0;
michael@0:     if (length <= 0x00400000u)
michael@0:         return (length & 0x00003fff) == 0;
michael@0:     if (length <= 0x01000000u)
michael@0:         return (length & 0x0000ffff) == 0;
michael@0:     if (length <= 0x04000000u)
michael@0:         return (length & 0x0003ffff) == 0;
michael@0:     if (length <= 0x10000000u)
michael@0:         return (length & 0x000fffff) == 0;
michael@0:     if (length <= 0x40000000u)
michael@0:         return (length & 0x003fffff) == 0;
michael@0:     if (length <= 0xff000000u)
michael@0:         return (length & 0x00ffffff) == 0;
michael@0:     return false;
michael@0: }
michael@0: 
michael@0: } // namespace js
michael@0: 
michael@0: #endif // jit_AsmJS_h