[WebAssembly] Write initial memory in pages not bytes

Subscribers: jfb, dschuff

Differential Revision: https://reviews.llvm.org/D32660

llvm-svn: 301687

5 files changed, 29 insertions, 3 deletions

diff --git a/llvm/include/llvm/Support/Wasm.h b/llvm/include/llvm/Support/Wasm.h
index 8e6c418c818..b02fcb19e3d 100644
--- a/llvm/include/llvm/Support/Wasm.h
+++ b/llvm/include/llvm/Support/Wasm.h
@@ -24,6 +24,8 @@ namespace wasm {
 const char WasmMagic[] = {'\0', 'a', 's', 'm'};
 // Wasm binary format version
 const uint32_t WasmVersion = 0x1;
+// Wasm uses a 64k page size
+const uint32_t WasmPageSize = 65536;
 
 struct WasmObjectHeader {
   StringRef Magic;
diff --git a/llvm/lib/MC/WasmObjectWriter.cpp b/llvm/lib/MC/WasmObjectWriter.cpp
index 6444046a30d..ae66829741b 100644
--- a/llvm/lib/MC/WasmObjectWriter.cpp
+++ b/llvm/lib/MC/WasmObjectWriter.cpp
@@ -913,12 +913,14 @@ void WasmObjectWriter::writeObject(MCAssembler &Asm,
   // 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);
 
diff --git a/llvm/test/MC/WebAssembly/sections.ll b/llvm/test/MC/WebAssembly/sections.ll
index e7ae2b3beea..85bf0818509 100644
--- a/llvm/test/MC/WebAssembly/sections.ll
+++ b/llvm/test/MC/WebAssembly/sections.ll
@@ -32,6 +32,11 @@ entry:
 ; CHECK:  }
 ; CHECK:  Section {
 ; CHECK:    Type: MEMORY (0x5)
+; CHECK:    Memories [
+; CHECK:      Memory {
+; CHECK:        InitialPages: 1
+; CHECK:      }
+; CHECK:    ]
 ; CHECK:  }
 ; CHECK:  Section {
 ; CHECK:    Type: GLOBAL (0x6)
diff --git a/llvm/test/tools/llvm-readobj/sections.test b/llvm/test/tools/llvm-readobj/sections.test
index 312c47fe4c8..1747ee45d4f 100644
--- a/llvm/test/tools/llvm-readobj/sections.test
+++ b/llvm/test/tools/llvm-readobj/sections.test
@@ -518,6 +518,11 @@ 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)
diff --git a/llvm/tools/llvm-readobj/WasmDumper.cpp b/llvm/tools/llvm-readobj/WasmDumper.cpp
index f07dd07b59f..21614297e46 100644
--- a/llvm/tools/llvm-readobj/WasmDumper.cpp
+++ b/llvm/tools/llvm-readobj/WasmDumper.cpp
@@ -150,8 +150,20 @@ void WasmDumper::printSections() {
     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) {