diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/s2wasm-main.cpp | 2 | ||||
| -rw-r--r-- | src/s2wasm.h | 59 | ||||
| -rw-r--r-- | src/support/utilities.h | 13 |
3 files changed, 40 insertions, 34 deletions
diff --git a/src/s2wasm-main.cpp b/src/s2wasm-main.cpp index 80284975b..d26ef3f1c 100644 --- a/src/s2wasm-main.cpp +++ b/src/s2wasm-main.cpp @@ -80,7 +80,7 @@ int main(int argc, const char *argv[]) { AllocatingModule wasm; uint64_t globalBase = options.extra.find("global-base") != options.extra.end() ? std::stoull(options.extra["global-base"]) - : 1; + : 0; uint64_t stackAllocation = options.extra.find("stack-allocation") != options.extra.end() ? std::stoull(options.extra["stack-allocation"]) diff --git a/src/s2wasm.h b/src/s2wasm.h index 2938cfae7..19b3db79d 100644 --- a/src/s2wasm.h +++ b/src/s2wasm.h @@ -58,7 +58,6 @@ class S2WasmBuilder { startFunction(startFunction), globalBase(globalBase), nextStatic(globalBase), - minInitialMemory(0), userInitialMemory(userInitialMemory), userMaxMemory(userMaxMemory) { if (userMaxMemory && userMaxMemory < userInitialMemory) { @@ -74,13 +73,15 @@ class S2WasmBuilder { s = input; scan(); s = input; + // Don't allow anything to be allocated at address 0 + if (globalBase == 0) nextStatic = 1; // Place the stack pointer at the bottom of the linear memory, to keep its // address small (and thus with a small encoding). placeStackPointer(stackAllocation); process(); // Place the stack after the user's static data, to keep those addresses // small. - if (stackAllocation) placeStack(stackAllocation); + if (stackAllocation) allocateStatic(stackAllocation, 16, ".stack"); fix(); } @@ -90,7 +91,6 @@ class S2WasmBuilder { size_t globalBase, // where globals can start to be statically allocated, i.e., the data segment nextStatic; // location of next static allocation std::map<Name, int32_t> staticAddresses; // name => address - size_t minInitialMemory; // Minimum initial size (in bytes) of memory. size_t userInitialMemory; // Initial memory size (in bytes) specified by the user. size_t userMaxMemory; // Max memory size (in bytes) specified by the user. //(after linking, this is rounded and set on the wasm object in pages) @@ -420,32 +420,30 @@ class S2WasmBuilder { } } + // Allocate a static variable and return its address in linear memory + size_t allocateStatic(size_t allocSize, size_t alignment, Name name) { + size_t address = alignAddr(nextStatic, alignment); + staticAddresses[name] = address; + nextStatic = address + allocSize; + return address; + } + void placeStackPointer(size_t stackAllocation) { - assert(nextStatic == globalBase); // we are the first allocation - // Allocate space for the stack pointer - staticAddresses["__stack_pointer"] = nextStatic; + assert(nextStatic == globalBase || nextStatic == 1); // we are the first allocation const size_t pointerSize = 4; + // Unconditionally allocate space for the stack pointer. Emscripten + // allocates the stack itself, and initializes the stack pointer itself. + size_t address = allocateStatic(pointerSize, pointerSize, "__stack_pointer"); if (stackAllocation) { - // If we are also allocating the stack, initialize the stack pointer to - // point to one past-the-end of the stack allocation. + // If we are allocating the stack, set up a relocation to initialize the + // stack pointer to point to one past-the-end of the stack allocation. auto* raw = new uint32_t; relocations.emplace_back(raw, ".stack", stackAllocation); assert(wasm.memory.segments.size() == 0); - addressSegments[nextStatic] = wasm.memory.segments.size(); + addressSegments[address] = wasm.memory.segments.size(); wasm.memory.segments.emplace_back( - nextStatic, reinterpret_cast<char*>(raw), pointerSize); - minInitialMemory = nextStatic + pointerSize; + address, reinterpret_cast<char*>(raw), pointerSize); } - nextStatic += pointerSize; - } - - void placeStack(size_t stackAllocation) { - // Allocate space for a user stack. It starts zeroed-out so needs no segment - // Round to a 16-byte aligned address. - nextStatic = (nextStatic + 15) & static_cast<size_t>(-16); - staticAddresses[".stack"] = nextStatic; - nextStatic += stackAllocation; - minInitialMemory = nextStatic; } void process() { @@ -1200,14 +1198,11 @@ class S2WasmBuilder { relocations[r].data = (uint32_t*)&(*raw)[i]; } // assign the address, add to memory - while (nextStatic % align) nextStatic++; - staticAddresses[name] = nextStatic; + size_t address = allocateStatic(size, align, name); if (!zero) { - addressSegments[nextStatic] = wasm.memory.segments.size(); - wasm.memory.segments.emplace_back(nextStatic, (const char*)&(*raw)[0], size); + addressSegments[address] = wasm.memory.segments.size(); + wasm.memory.segments.emplace_back(address, (const char*)&(*raw)[0], size); } - nextStatic += size; - minInitialMemory = nextStatic; } void parseLcomm(Name name, size_t align=1) { @@ -1218,10 +1213,7 @@ class S2WasmBuilder { skipComma(); getInt(); } - while (nextStatic % align) nextStatic++; - staticAddresses[name] = nextStatic; - nextStatic += size; - minInitialMemory = nextStatic; + allocateStatic(size, align, name); } void skipImports() { @@ -1240,9 +1232,10 @@ class S2WasmBuilder { } void fix() { - // Round the memory size up to a page, and update the page-increment versions + // The minimum initial memory size is the amount of static variables we have + // allocated. Round it up to a page, and update the page-increment versions // of initial and max - size_t initialMem = roundUpToPageSize(minInitialMemory); + size_t initialMem = roundUpToPageSize(nextStatic); if (userInitialMemory) { if (initialMem > userInitialMemory) { Fatal() << "Specified initial memory size " << userInitialMemory << diff --git a/src/support/utilities.h b/src/support/utilities.h index 77263a78e..d35b2b34a 100644 --- a/src/support/utilities.h +++ b/src/support/utilities.h @@ -35,6 +35,19 @@ inline Destination bit_cast(const Source& source) { return destination; } +inline bool isPowerOf2(uint32_t v) { + return v && !(v & (v - 1)); +} + +inline size_t alignAddr(size_t address, size_t alignment) { + assert(alignment && isPowerOf2((uint32_t)alignment) && + "Alignment is not a power of two!"); + + assert(address + alignment - 1 >= address); + + return ((address + alignment - 1) & ~(alignment - 1)); +} + } // namespace wasm #endif // wasm_support_utilities_h |