[WebAssembly] Write initial memory in pages not bytes

[dschuff]

include/llvm/Support/Wasm.h

27

i guess we'd probably call this 64k :D

[sbc100]

• fix typo

include/llvm/Support/Wasm.h

 
 namespace llvm {
 namespace wasm {
 
 // Object file magic string.
 const char WasmMagic[] = {'\0', 'a', 's', 'm'};
 // Wasm binary format version
 const uint32_t WasmVersion = 0x1;
+// Wasm uses a 65k page size
+const uint32_t WasmPageSize = 65536;
 
 struct WasmObjectHeader {
   StringRef Magic;
   uint32_t Version;
 };
 
 struct WasmSignature {
   std::vector<int32_t> ParamTypes;

lib/MC/WasmObjectWriter.cpp

void WasmObjectWriter::writeObject(MCAssembler &Asm,
   encodeULEB128(TableElems.size(), getStream()); // initial
 
   endSection(Section);
 
   // === Memory Section ========================================================
   // For now, always emit the memory section, since loads and stores are not
   // valid without it. In the future, we could perhaps be more clever and omit
   // it if there are no loads or stores.
-  startSection(Section, wasm::WASM_SEC_MEMORY);
+  uint32_t NumPages =
+      (DataBytes.size() + wasm::WasmPageSize - 1) / wasm::WasmPageSize;
 
+  startSection(Section, wasm::WASM_SEC_MEMORY);
   encodeULEB128(1, getStream()); // number of memory spaces
 
   encodeULEB128(0, getStream()); // flags
-  encodeULEB128(DataBytes.size(), getStream()); // initial
+  encodeULEB128(NumPages, getStream()); // initial
 
   endSection(Section);
 
   // === Global Section ========================================================
   if (!Globals.empty()) {
     startSection(Section, wasm::WASM_SEC_GLOBAL);
 
     encodeULEB128(Globals.size(), getStream());

test/MC/WebAssembly/sections.ll

 ; CHECK:  Section {
 ; CHECK:    Type: FUNCTION (0x3)
 ; CHECK:  }
 ; CHECK:  Section {
 ; CHECK:    Type: TABLE (0x4)
 ; CHECK:  }
 ; CHECK:  Section {
 ; CHECK:    Type: MEMORY (0x5)
+; CHECK:    Memories [
+; CHECK:      Memory {
+; CHECK:        InitialPages: 1
+; CHECK:      }
+; CHECK:    ]
 ; CHECK:  }
 ; CHECK:  Section {
 ; CHECK:    Type: GLOBAL (0x6)
 ; CHECK:  }
 ; CHECK:  Section {
 ; CHECK:    Type: EXPORT (0x7)
 ; CHECK:  }
 ; CHECK:  Section {

test/tools/llvm-readobj/sections.test

 WASM-NEXT:    Type: TABLE (0x4)
 WASM-NEXT:    Size: 4
 WASM-NEXT:    Offset: 56
 WASM-NEXT:  }
 WASM-NEXT:  Section {
 WASM-NEXT:    Type: MEMORY (0x5)
 WASM-NEXT:    Size: 3
 WASM-NEXT:    Offset: 66
+WASM-NEXT:    Memories [
+WASM-NEXT:      Memory {
+WASM-NEXT:        InitialPages: 0
+WASM-NEXT:      }
+WASM-NEXT:    ]
 WASM-NEXT:  }
 WASM-NEXT:  Section {
 WASM-NEXT:    Type: EXPORT (0x7)
 WASM-NEXT:    Size: 7
 WASM-NEXT:    Offset: 75
 WASM-NEXT:  }
 WASM-NEXT:  Section {
 WASM-NEXT:    Type: ELEM (0x9)

tools/llvm-readobj/WasmDumper.cpp

 void WasmDumper::printSections() {
   ListScope Group(W, "Sections");
   for (const SectionRef &Section : Obj->sections()) {
     const WasmSection &WasmSec = Obj->getWasmSection(Section);
     DictScope SectionD(W, "Section");
     W.printEnum("Type", WasmSec.Type, makeArrayRef(WasmSectionTypes));
     W.printNumber("Size", (uint64_t)WasmSec.Content.size());
     W.printNumber("Offset", WasmSec.Offset);
-    if (WasmSec.Type == wasm::WASM_SEC_CUSTOM) {
+    switch (WasmSec.Type) {
+    case wasm::WASM_SEC_CUSTOM:
       W.printString("Name", WasmSec.Name);
+      break;
+    case wasm::WASM_SEC_MEMORY:
+      ListScope Group(W, "Memories");
+      for (const wasm::WasmLimits &Memory : Obj->memories()) {
+        DictScope Group(W, "Memory");
+        W.printNumber("InitialPages", Memory.Initial);
+        if (Memory.Flags & wasm::WASM_LIMITS_FLAG_HAS_MAX) {
+          W.printNumber("MaxPages", WasmSec.Offset);
+        }
+      }
+      break;
     }
 
     if (opts::SectionRelocations) {
       ListScope D(W, "Relocations");
       for (const RelocationRef &Reloc : Section.relocations())
         printRelocation(Section, Reloc);
     }