diff options
| -rw-r--r-- | src/s2wasm-main.cpp | 11 | ||||
| -rw-r--r-- | src/s2wasm.h | 34 |
2 files changed, 40 insertions, 5 deletions
diff --git a/src/s2wasm-main.cpp b/src/s2wasm-main.cpp index c3f3d0a2f..e75147b75 100644 --- a/src/s2wasm-main.cpp +++ b/src/s2wasm-main.cpp @@ -46,6 +46,11 @@ int main(int argc, const char *argv[]) { [](Options *o, const std::string &argument) { o->extra["global-base"] = argument; }) + .add("--allocate-stack", "-s", "Size of the user stack in linear memory", + Options::Arguments::One, + [](Options *o, const std::string &argument) { + o->extra["stack-allocation"] = argument; + }) .add_positional("INFILE", Options::Arguments::One, [](Options *o, const std::string &argument) { o->extra["infile"] = argument; @@ -59,9 +64,13 @@ int main(int argc, const char *argv[]) { size_t globalBase = options.extra.find("global-base") != options.extra.end() ? std::stoull(options.extra["global-base"]) : 1; + size_t stackAllocation = + options.extra.find("stack-allocation") != options.extra.end() + ? std::stoull(options.extra["stack-allocation"]) + : 0; if (options.debug) std::cerr << "Global base " << globalBase << '\n'; S2WasmBuilder s2wasm(wasm, input.c_str(), options.debug, globalBase, - ignoreUnknownSymbols); + stackAllocation, ignoreUnknownSymbols); if (options.debug) std::cerr << "Emscripten gluing..." << std::endl; std::stringstream meta; diff --git a/src/s2wasm.h b/src/s2wasm.h index 2a2a36028..1e0a28b43 100644 --- a/src/s2wasm.h +++ b/src/s2wasm.h @@ -42,7 +42,8 @@ class S2WasmBuilder { public: S2WasmBuilder(AllocatingModule& wasm, const char* input, bool debug, - size_t globalBase, bool ignoreUnknownSymbols) + size_t globalBase, size_t stackAllocation, + bool ignoreUnknownSymbols) : wasm(wasm), allocator(wasm.allocator), debug(debug), @@ -52,8 +53,13 @@ class S2WasmBuilder { s = input; scan(); s = input; - prepare(); + // 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); fix(); } @@ -370,10 +376,30 @@ class S2WasmBuilder { } } - void prepare() { + void placeStackPointer(size_t stackAllocation) { assert(nextStatic == globalBase); // we are the first allocation + // Allocate space for the stack pointer staticAddresses["__stack_pointer"] = nextStatic; - nextStatic += 4; + const size_t pointerSize = 4; + if (stackAllocation) { + // If we are also allocating the stack, 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(); + wasm.memory.segments.emplace_back( + nextStatic, reinterpret_cast<char*>(raw), pointerSize); + wasm.memory.initial = nextStatic + pointerSize; + } + nextStatic += pointerSize; + } + + void placeStack(size_t stackAllocation) { + // Allocate space for a user stack. It starts zeroed-out so needs no segment + staticAddresses[".stack"] = nextStatic; + nextStatic += stackAllocation; + wasm.memory.initial = nextStatic; } void process() { |