Add flag to s2wasm to export __growWasmMemory function (#696)

* Add a flag to s2wasm to export grow_memory

Binaryen's wasm.js-post.js calls back in to wasm in order to grow the
linear memory, via a function that asm2wasm exports called
__growWasmMemory.
This changes exposes that method through s2wasm when invoked with a
flag.

* Move AsmConstWalker from wasm-linker to wasm-emscripten

* Add test for memory growth in s2wasm

* Move makeDynCallThunks into wasm-emscripten module

* Move mutation in getTableSegment into a separate method

* Move emscripten metadata generation into wasm-emscripten

Also make AsmConstWalker internal to the wasm-emscripten module, as it's only used for the metadata pass.

1 files changed, 16 insertions, 0 deletions

diff --git a/src/tools/s2wasm.cpp b/src/tools/s2wasm.cpp
index 2ee094af4..8c36a0d58 100644
--- a/src/tools/s2wasm.cpp
+++ b/src/tools/s2wasm.cpp
@@ -22,6 +22,7 @@
 #include "support/command-line.h"
 #include "support/file.h"
 #include "s2wasm.h"
+#include "wasm-emscripten.h"
 #include "wasm-linker.h"
 #include "wasm-printing.h"
 #include "wasm-validator.h"
@@ -32,6 +33,7 @@ using namespace wasm;
 int main(int argc, const char *argv[]) {
   bool ignoreUnknownSymbols = false;
   bool generateEmscriptenGlue = false;
+  bool allowMemoryGrowth = false;
   std::string startFunction;
   std::vector<std::string> archiveLibraries;
   Options options("s2wasm", "Link .s file into .wast");
@@ -73,6 +75,11 @@ int main(int argc, const char *argv[]) {
            [](Options *o, const std::string &argument) {
              o->extra["max-memory"] = argument;
            })
+      .add("--allow-memory-growth", "", "Allow linear memory to grow at runtime",
+           Options::Arguments::Zero,
+           [&allowMemoryGrowth](Options *, const std::string &) {
+             allowMemoryGrowth = true;
+           })
       .add("--emscripten-glue", "-e", "Generate emscripten glue",
            Options::Arguments::Zero,
            [&generateEmscriptenGlue](Options *, const std::string &) {
@@ -98,6 +105,11 @@ int main(int argc, const char *argv[]) {
                       });
   options.parse(argc, argv);
 
+  if (allowMemoryGrowth && !generateEmscriptenGlue) {
+    Fatal() << "Error: adding memory growth code without Emscripten glue. "
+      "This doesn't do anything.\n";
+  }
+
   auto debugFlag = options.debug ? Flags::Debug : Flags::Release;
   auto input(read_file<std::string>(options.extra["infile"], Flags::Text, debugFlag));
 
@@ -138,6 +150,10 @@ int main(int argc, const char *argv[]) {
   std::stringstream meta;
   if (generateEmscriptenGlue) {
     if (options.debug) std::cerr << "Emscripten gluing..." << std::endl;
+    if (allowMemoryGrowth) {
+      emscripten::generateMemoryGrowthFunction(linker.getOutput().wasm);
+    }
+
     // dyncall thunks
     linker.emscriptenGlue(meta);
   }