Add support for the custom-page-sizes proposal (#2502)

This adds support in the binary/text parsers and writers,
the validator and interpreter, and objdump (but not wasm2c).

44 files changed, 602 insertions, 132 deletions

diff --git a/README.md b/README.md
index a6122ee4..d0ae81a3 100644
--- a/README.md
+++ b/README.md
@@ -62,6 +62,7 @@ Wabt has been compiled to JavaScript via emscripten. Some of the functionality i
 | [multi-memory][]      | `--enable-multi-memory`     |   | ✓ | ✓ | ✓ | ✓ | ✓ |
 | [extended-const][]    | `--enable-extended-const`   |   | ✓ | ✓ | ✓ | ✓ | ✓ |
 | [relaxed-simd][]      | `--enable-relaxed-simd`     |   | ✓ | ✓ | ✓ | ✓ |   |
+| [custom-page-sizes][] | `--enable-custom-page-sizes`|   | ✓ | ✓ | ✓ | ✓ |   |
 
 [exception handling]: https://github.com/WebAssembly/exception-handling
 [mutable globals]: https://github.com/WebAssembly/mutable-global
@@ -78,6 +79,7 @@ Wabt has been compiled to JavaScript via emscripten. Some of the functionality i
 [multi-memory]: https://github.com/WebAssembly/multi-memory
 [extended-const]: https://github.com/WebAssembly/extended-const
 [relaxed-simd]: https://github.com/WebAssembly/relaxed-simd
+[custom-page-sizes]: https://github.com/WebAssembly/custom-page-sizes
 
 ## Cloning
 
diff --git a/include/wabt/binary-reader-logging.h b/include/wabt/binary-reader-logging.h
index fee211f9..fd166011 100644
--- a/include/wabt/binary-reader-logging.h
+++ b/include/wabt/binary-reader-logging.h
@@ -74,7 +74,8 @@ class BinaryReaderLogging : public BinaryReaderDelegate {
                         std::string_view module_name,
                         std::string_view field_name,
                         Index memory_index,
-                        const Limits* page_limits) override;
+                        const Limits* page_limits,
+                        uint32_t page_size) override;
   Result OnImportGlobal(Index import_index,
                         std::string_view module_name,
                         std::string_view field_name,
@@ -102,7 +103,9 @@ class BinaryReaderLogging : public BinaryReaderDelegate {
 
   Result BeginMemorySection(Offset size) override;
   Result OnMemoryCount(Index count) override;
-  Result OnMemory(Index index, const Limits* limits) override;
+  Result OnMemory(Index index,
+                  const Limits* limits,
+                  uint32_t page_size) override;
   Result EndMemorySection() override;
 
   Result BeginGlobalSection(Offset size) override;
diff --git a/include/wabt/binary-reader-nop.h b/include/wabt/binary-reader-nop.h
index c7ec78b1..85906062 100644
--- a/include/wabt/binary-reader-nop.h
+++ b/include/wabt/binary-reader-nop.h
@@ -89,7 +89,8 @@ class BinaryReaderNop : public BinaryReaderDelegate {
                         std::string_view module_name,
                         std::string_view field_name,
                         Index memory_index,
-                        const Limits* page_limits) override {
+                        const Limits* page_limits,
+                        uint32_t page_size) override {
     return Result::Ok;
   }
   Result OnImportGlobal(Index import_index,
@@ -130,7 +131,9 @@ class BinaryReaderNop : public BinaryReaderDelegate {
   /* Memory section */
   Result BeginMemorySection(Offset size) override { return Result::Ok; }
   Result OnMemoryCount(Index count) override { return Result::Ok; }
-  Result OnMemory(Index index, const Limits* limits) override {
+  Result OnMemory(Index index,
+                  const Limits* limits,
+                  uint32_t page_size) override {
     return Result::Ok;
   }
   Result EndMemorySection() override { return Result::Ok; }
diff --git a/include/wabt/binary-reader.h b/include/wabt/binary-reader.h
index 3d48f574..90161264 100644
--- a/include/wabt/binary-reader.h
+++ b/include/wabt/binary-reader.h
@@ -125,7 +125,8 @@ class BinaryReaderDelegate {
                                 std::string_view module_name,
                                 std::string_view field_name,
                                 Index memory_index,
-                                const Limits* page_limits) = 0;
+                                const Limits* page_limits,
+                                uint32_t page_size) = 0;
   virtual Result OnImportGlobal(Index import_index,
                                 std::string_view module_name,
                                 std::string_view field_name,
@@ -156,7 +157,9 @@ class BinaryReaderDelegate {
   /* Memory section */
   virtual Result BeginMemorySection(Offset size) = 0;
   virtual Result OnMemoryCount(Index count) = 0;
-  virtual Result OnMemory(Index index, const Limits* limits) = 0;
+  virtual Result OnMemory(Index index,
+                          const Limits* limits,
+                          uint32_t page_size) = 0;
   virtual Result EndMemorySection() = 0;
 
   /* Global section */
diff --git a/include/wabt/binary.h b/include/wabt/binary.h
index ecf11a79..98575f96 100644
--- a/include/wabt/binary.h
+++ b/include/wabt/binary.h
@@ -24,7 +24,12 @@
 #define WABT_BINARY_LIMITS_HAS_MAX_FLAG 0x1
 #define WABT_BINARY_LIMITS_IS_SHARED_FLAG 0x2
 #define WABT_BINARY_LIMITS_IS_64_FLAG 0x4
-#define WABT_BINARY_LIMITS_ALL_FLAGS                                     \
+#define WABT_BINARY_LIMITS_HAS_CUSTOM_PAGE_SIZE_FLAG 0x8
+#define WABT_BINARY_LIMITS_ALL_MEMORY_FLAGS                              \
+  (WABT_BINARY_LIMITS_HAS_MAX_FLAG | WABT_BINARY_LIMITS_IS_SHARED_FLAG | \
+   WABT_BINARY_LIMITS_IS_64_FLAG |                                       \
+   WABT_BINARY_LIMITS_HAS_CUSTOM_PAGE_SIZE_FLAG)
+#define WABT_BINARY_LIMITS_ALL_TABLE_FLAGS                               \
   (WABT_BINARY_LIMITS_HAS_MAX_FLAG | WABT_BINARY_LIMITS_IS_SHARED_FLAG | \
    WABT_BINARY_LIMITS_IS_64_FLAG)
 
diff --git a/include/wabt/common.h b/include/wabt/common.h
index 12b2eb09..6962f06d 100644
--- a/include/wabt/common.h
+++ b/include/wabt/common.h
@@ -44,14 +44,18 @@
 #define WABT_USE(x) static_cast<void>(x)
 
 // 64k
-#define WABT_PAGE_SIZE 0x10000
-// # of pages that fit in 32-bit address space
-#define WABT_MAX_PAGES32 0x10000
-// # of pages that fit in 64-bit address space
-#define WABT_MAX_PAGES64 0x1000000000000
-#define WABT_BYTES_TO_PAGES(x) ((x) >> 16)
-#define WABT_ALIGN_UP_TO_PAGE(x) \
-  (((x) + WABT_PAGE_SIZE - 1) & ~(WABT_PAGE_SIZE - 1))
+#define WABT_DEFAULT_PAGE_SIZE 0x10000
+
+inline uint64_t WABT_BYTES_TO_MIN_PAGES(uint64_t num_bytes,
+                                        uint32_t page_size) {
+  if ((page_size == 0) ||
+      (page_size & (page_size - 1))) {  // malformed page sizes
+    WABT_UNREACHABLE;
+    return 0;
+  }
+  uint64_t num_pages = num_bytes / page_size;
+  return (page_size * num_pages == num_bytes) ? num_pages : num_pages + 1;
+}
 
 #define WABT_ENUM_COUNT(name) \
   (static_cast<int>(name::Last) - static_cast<int>(name::First) + 1)
diff --git a/include/wabt/feature.def b/include/wabt/feature.def
index 00a4e7f2..ac96377b 100644
--- a/include/wabt/feature.def
+++ b/include/wabt/feature.def
@@ -40,3 +40,4 @@ WABT_FEATURE(memory64,            "memory64",                false,   "64-bit me
 WABT_FEATURE(multi_memory,        "multi-memory",            false,   "Multi-memory")
 WABT_FEATURE(extended_const,      "extended-const",          false,   "Extended constant expressions")
 WABT_FEATURE(relaxed_simd,        "relaxed-simd",            false,   "Relaxed SIMD")
+WABT_FEATURE(custom_page_sizes,   "custom-page-sizes",       false,   "Custom page sizes")
diff --git a/include/wabt/interp/interp-inl.h b/include/wabt/interp/interp-inl.h
index 1f3402c6..a9ac4a34 100644
--- a/include/wabt/interp/interp-inl.h
+++ b/include/wabt/interp/interp-inl.h
@@ -64,11 +64,12 @@ inline bool MemoryType::classof(const ExternType* type) {
   return type->kind == skind;
 }
 
-inline MemoryType::MemoryType(Limits limits)
-    : ExternType(ExternKind::Memory), limits(limits) {
+inline MemoryType::MemoryType(Limits limits, uint32_t page_size)
+    : ExternType(ExternKind::Memory), limits(limits), page_size(page_size) {
   // Always set max.
   if (!limits.has_max) {
-    this->limits.max = limits.is_64 ? WABT_MAX_PAGES64 : WABT_MAX_PAGES32;
+    this->limits.max = WABT_BYTES_TO_MIN_PAGES(
+        (limits.is_64 ? UINT64_MAX : UINT32_MAX), page_size);
   }
 }
 
diff --git a/include/wabt/interp/interp.h b/include/wabt/interp/interp.h
index 069bedaa..821a5391 100644
--- a/include/wabt/interp/interp.h
+++ b/include/wabt/interp/interp.h
@@ -206,7 +206,7 @@ struct MemoryType : ExternType {
   static const ExternKind skind = ExternKind::Memory;
   static bool classof(const ExternType* type);
 
-  explicit MemoryType(Limits);
+  explicit MemoryType(Limits, uint32_t);
 
   std::unique_ptr<ExternType> Clone() const override;
 
@@ -215,6 +215,7 @@ struct MemoryType : ExternType {
                       std::string* out_msg);
 
   Limits limits;
+  uint32_t page_size;
 };
 
 struct GlobalType : ExternType {
diff --git a/include/wabt/ir.h b/include/wabt/ir.h
index 80e1c2a8..e300b66c 100644
--- a/include/wabt/ir.h
+++ b/include/wabt/ir.h
@@ -947,6 +947,7 @@ struct Memory {
 
   std::string name;
   Limits page_limits;
+  uint32_t page_size;
 };
 
 struct DataSegment {
diff --git a/include/wabt/shared-validator.h b/include/wabt/shared-validator.h
index 32add012..df02b594 100644
--- a/include/wabt/shared-validator.h
+++ b/include/wabt/shared-validator.h
@@ -75,7 +75,7 @@ class SharedValidator {
 
   Result OnFunction(const Location&, Var sig_var);
   Result OnTable(const Location&, Type elem_type, const Limits&);
-  Result OnMemory(const Location&, const Limits&);
+  Result OnMemory(const Location&, const Limits&, uint32_t page_size);
   Result OnGlobalImport(const Location&, Type type, bool mutable_);
   Result OnGlobal(const Location&, Type type, bool mutable_);
   Result OnTag(const Location&, Var sig_var);
diff --git a/include/wabt/token.def b/include/wabt/token.def
index 1fd3d0e5..53d1fabb 100644
--- a/include/wabt/token.def
+++ b/include/wabt/token.def
@@ -57,6 +57,7 @@ WABT_TOKEN(NanArithmetic, "nan:arithmetic")
 WABT_TOKEN(NanCanonical, "nan:canonical")
 WABT_TOKEN(Offset, "offset")
 WABT_TOKEN(Output, "output")
+WABT_TOKEN(PageSize, "pagesize")
 WABT_TOKEN(Param, "param")
 WABT_TOKEN(Ref, "ref")
 WABT_TOKEN(Quote, "quote")
diff --git a/include/wabt/wast-parser.h b/include/wabt/wast-parser.h
index 36447c58..8ba71e47 100644
--- a/include/wabt/wast-parser.h
+++ b/include/wabt/wast-parser.h
@@ -147,6 +147,7 @@ class WastParser {
   Result ParseMemidx(Location loc, Var* memidx);
   Result ParseLimitsIndex(Limits*);
   Result ParseLimits(Limits*);
+  Result ParsePageSize(uint32_t*);
   Result ParseNat(uint64_t*, bool is_64);
 
   Result ParseModuleFieldList(Module*);
diff --git a/src/binary-reader-ir.cc b/src/binary-reader-ir.cc
index 2ab3b098..04b2e90b 100644
--- a/src/binary-reader-ir.cc
+++ b/src/binary-reader-ir.cc
@@ -126,7 +126,8 @@ class BinaryReaderIR : public BinaryReaderNop {
                         std::string_view module_name,
                         std::string_view field_name,
                         Index memory_index,
-                        const Limits* page_limits) override;
+                        const Limits* page_limits,
+                        uint32_t page_size) override;
   Result OnImportGlobal(Index import_index,
                         std::string_view module_name,
                         std::string_view field_name,
@@ -148,7 +149,9 @@ class BinaryReaderIR : public BinaryReaderNop {
                  const Limits* elem_limits) override;
 
   Result OnMemoryCount(Index count) override;
-  Result OnMemory(Index index, const Limits* limits) override;
+  Result OnMemory(Index index,
+                  const Limits* limits,
+                  uint32_t page_size) override;
 
   Result OnGlobalCount(Index count) override;
   Result BeginGlobal(Index index, Type type, bool mutable_) override;
@@ -620,11 +623,13 @@ Result BinaryReaderIR::OnImportMemory(Index import_index,
                                       std::string_view module_name,
                                       std::string_view field_name,
                                       Index memory_index,
-                                      const Limits* page_limits) {
+                                      const Limits* page_limits,
+                                      uint32_t page_size) {
   auto import = std::make_unique<MemoryImport>();
   import->module_name = module_name;
   import->field_name = field_name;
   import->memory.page_limits = *page_limits;
+  import->memory.page_size = page_size;
   if (import->memory.page_limits.is_shared) {
     module_->features_used.threads = true;
   }
@@ -707,10 +712,13 @@ Result BinaryReaderIR::OnMemoryCount(Index count) {
   return Result::Ok;
 }
 
-Result BinaryReaderIR::OnMemory(Index index, const Limits* page_limits) {
+Result BinaryReaderIR::OnMemory(Index index,
+                                const Limits* page_limits,
+                                uint32_t page_size) {
   auto field = std::make_unique<MemoryModuleField>(GetLocation());
   Memory& memory = field->memory;
   memory.page_limits = *page_limits;
+  memory.page_size = page_size;
   if (memory.page_limits.is_shared) {
     module_->features_used.threads = true;
   }
diff --git a/src/binary-reader-logging.cc b/src/binary-reader-logging.cc
index ea427391..0c3fcda6 100644
--- a/src/binary-reader-logging.cc
+++ b/src/binary-reader-logging.cc
@@ -217,14 +217,15 @@ Result BinaryReaderLogging::OnImportMemory(Index import_index,
                                            std::string_view module_name,
                                            std::string_view field_name,
                                            Index memory_index,
-                                           const Limits* page_limits) {
+                                           const Limits* page_limits,
+                                           uint32_t page_size) {
   char buf[100];
   SPrintLimits(buf, sizeof(buf), page_limits);
   LOGF("OnImportMemory(import_index: %" PRIindex ", memory_index: %" PRIindex
        ", %s)\n",
        import_index, memory_index, buf);
   return reader_->OnImportMemory(import_index, module_name, field_name,
-                                 memory_index, page_limits);
+                                 memory_index, page_limits, page_size);
 }
 
 Result BinaryReaderLogging::OnImportGlobal(Index import_index,
@@ -264,11 +265,13 @@ Result BinaryReaderLogging::OnTable(Index index,
   return reader_->OnTable(index, elem_type, elem_limits);
 }
 
-Result BinaryReaderLogging::OnMemory(Index index, const Limits* page_limits) {
+Result BinaryReaderLogging::OnMemory(Index index,
+                                     const Limits* page_limits,
+                                     uint32_t page_size) {
   char buf[100];
   SPrintLimits(buf, sizeof(buf), page_limits);
   LOGF("OnMemory(index: %" PRIindex ", %s)\n", index, buf);
-  return reader_->OnMemory(index, page_limits);
+  return reader_->OnMemory(index, page_limits, page_size);
 }
 
 Result BinaryReaderLogging::BeginGlobal(Index index, Type type, bool mutable_) {
diff --git a/src/binary-reader-objdump.cc b/src/binary-reader-objdump.cc
index ff9afbc6..52e6d27a 100644
--- a/src/binary-reader-objdump.cc
+++ b/src/binary-reader-objdump.cc
@@ -1059,7 +1059,8 @@ class BinaryReaderObjdump : public BinaryReaderObjdumpBase {
                         std::string_view module_name,
                         std::string_view field_name,
                         Index memory_index,
-                        const Limits* page_limits) override;
+                        const Limits* page_limits,
+                        uint32_t page_size) override;
   Result OnImportGlobal(Index import_index,
                         std::string_view module_name,
                         std::string_view field_name,
@@ -1081,7 +1082,9 @@ class BinaryReaderObjdump : public BinaryReaderObjdumpBase {
                  const Limits* elem_limits) override;
 
   Result OnMemoryCount(Index count) override;
-  Result OnMemory(Index index, const Limits* limits) override;
+  Result OnMemory(Index index,
+                  const Limits* limits,
+                  uint32_t page_size) override;
 
   Result OnGlobalCount(Index count) override;
   Result BeginGlobal(Index index, Type type, bool mutable_) override;
@@ -1563,7 +1566,8 @@ Result BinaryReaderObjdump::OnImportMemory(Index import_index,
                                            std::string_view module_name,
                                            std::string_view field_name,
                                            Index memory_index,
-                                           const Limits* page_limits) {
+                                           const Limits* page_limits,
+                                           uint32_t page_size) {
   PrintDetails(" - memory[%" PRIindex "] pages: initial=%" PRId64, memory_index,
                page_limits->initial);
   if (page_limits->has_max) {
@@ -1575,6 +1579,9 @@ Result BinaryReaderObjdump::OnImportMemory(Index import_index,
   if (page_limits->is_64) {
     PrintDetails(" i64");
   }
+  if (page_size != WABT_DEFAULT_PAGE_SIZE) {
+    PrintDetails(" (pagesize %u)", page_size);
+  }
   PrintDetails(" <- " PRIstringview "." PRIstringview "\n",
                WABT_PRINTF_STRING_VIEW_ARG(module_name),
                WABT_PRINTF_STRING_VIEW_ARG(field_name));
@@ -1615,7 +1622,9 @@ Result BinaryReaderObjdump::OnMemoryCount(Index count) {
   return OnCount(count);
 }
 
-Result BinaryReaderObjdump::OnMemory(Index index, const Limits* page_limits) {
+Result BinaryReaderObjdump::OnMemory(Index index,
+                                     const Limits* page_limits,
+                                     uint32_t page_size) {
   PrintDetails(" - memory[%" PRIindex "] pages: initial=%" PRId64, index,
                page_limits->initial);
   if (page_limits->has_max) {
@@ -1627,6 +1636,9 @@ Result BinaryReaderObjdump::OnMemory(Index index, const Limits* page_limits) {
   if (page_limits->is_64) {
     PrintDetails(" i64");
   }
+  if (page_size != WABT_DEFAULT_PAGE_SIZE) {
+    PrintDetails(" (pagesize %u)", page_size);
+  }
   PrintDetails("\n");
   return Result::Ok;
 }
diff --git a/src/binary-reader.cc b/src/binary-reader.cc
index 33801a7d..18b57e05 100644
--- a/src/binary-reader.cc
+++ b/src/binary-reader.cc
@@ -146,7 +146,8 @@ class BinaryReader {
 
   [[nodiscard]] Result ReadInitExpr(Index index);
   [[nodiscard]] Result ReadTable(Type* out_elem_type, Limits* out_elem_limits);
-  [[nodiscard]] Result ReadMemory(Limits* out_page_limits);
+  [[nodiscard]] Result ReadMemory(Limits* out_page_limits,
+                                  uint32_t* out_page_size);
   [[nodiscard]] Result ReadGlobalHeader(Type* out_type, bool* out_mutable);
   [[nodiscard]] Result ReadTagType(Index* out_sig_index);
   [[nodiscard]] Result ReadAddress(Address* out_value,
@@ -600,7 +601,7 @@ Result BinaryReader::ReadTable(Type* out_elem_type, Limits* out_elem_limits) {
   bool has_max = flags & WABT_BINARY_LIMITS_HAS_MAX_FLAG;
   bool is_shared = flags & WABT_BINARY_LIMITS_IS_SHARED_FLAG;
   bool is_64 = flags & WABT_BINARY_LIMITS_IS_64_FLAG;
-  const uint8_t unknown_flags = flags & ~WABT_BINARY_LIMITS_ALL_FLAGS;
+  const uint8_t unknown_flags = flags & ~WABT_BINARY_LIMITS_ALL_TABLE_FLAGS;
   ERROR_IF(is_shared, "tables may not be shared");
   ERROR_IF(is_64 && !options_.features.memory64_enabled(),
            "memory64 not allowed");
@@ -617,7 +618,8 @@ Result BinaryReader::ReadTable(Type* out_elem_type, Limits* out_elem_limits) {
   return Result::Ok;
 }
 
-Result BinaryReader::ReadMemory(Limits* out_page_limits) {
+Result BinaryReader::ReadMemory(Limits* out_page_limits,
+                                uint32_t* out_page_size) {
   uint8_t flags;
   uint64_t initial;
   uint64_t max = 0;
@@ -625,12 +627,17 @@ Result BinaryReader::ReadMemory(Limits* out_page_limits) {
   bool has_max = flags & WABT_BINARY_LIMITS_HAS_MAX_FLAG;
   bool is_shared = flags & WABT_BINARY_LIMITS_IS_SHARED_FLAG;
   bool is_64 = flags & WABT_BINARY_LIMITS_IS_64_FLAG;
-  const uint8_t unknown_flags = flags & ~WABT_BINARY_LIMITS_ALL_FLAGS;
+  bool has_custom_page_size =
+      flags & WABT_BINARY_LIMITS_HAS_CUSTOM_PAGE_SIZE_FLAG;
+  const uint8_t unknown_flags = flags & ~WABT_BINARY_LIMITS_ALL_MEMORY_FLAGS;
   ERROR_UNLESS(unknown_flags == 0, "malformed memory limits flag: %d", flags);
   ERROR_IF(is_shared && !options_.features.threads_enabled(),
            "memory may not be shared: threads not allowed");
   ERROR_IF(is_64 && !options_.features.memory64_enabled(),
            "memory64 not allowed");
+  ERROR_IF(
+      has_custom_page_size && !options_.features.custom_page_sizes_enabled(),
+      "custom page sizes not allowed");
   if (options_.features.memory64_enabled()) {
     CHECK_RESULT(ReadU64Leb128(&initial, "memory initial page count"));
     if (has_max) {
@@ -646,6 +653,14 @@ Result BinaryReader::ReadMemory(Limits* out_page_limits) {
       max = max32;
     }
   }
+  if (has_custom_page_size) {
+    uint32_t page_size_log2;
+    CHECK_RESULT(ReadU32Leb128(&page_size_log2, "memory page size"));
+    ERROR_IF(page_size_log2 > 16, "malformed memory page size");
+    *out_page_size = 1 << page_size_log2;
+  } else {
+    *out_page_size = WABT_DEFAULT_PAGE_SIZE;
+  }
 
   out_page_limits->has_max = has_max;
   out_page_limits->is_shared = is_shared;
@@ -2586,9 +2601,10 @@ Result BinaryReader::ReadImportSection(Offset section_size) {
 
       case ExternalKind::Memory: {
         Limits page_limits;
-        CHECK_RESULT(ReadMemory(&page_limits));
+        uint32_t page_size;
+        CHECK_RESULT(ReadMemory(&page_limits, &page_size));
         CALLBACK(OnImportMemory, i, module_name, field_name,
-                 num_memory_imports_, &page_limits);
+                 num_memory_imports_, &page_limits, page_size);
         num_memory_imports_++;
         break;
       }
@@ -2663,8 +2679,9 @@ Result BinaryReader::ReadMemorySection(Offset section_size) {
   for (Index i = 0; i < num_memories; ++i) {
     Index memory_index = num_memory_imports_ + i;
     Limits page_limits;
-    CHECK_RESULT(ReadMemory(&page_limits));
-    CALLBACK(OnMemory, memory_index, &page_limits);
+    uint32_t page_size;
+    CHECK_RESULT(ReadMemory(&page_limits, &page_size));
+    CALLBACK(OnMemory, memory_index, &page_limits, page_size);
   }
   CALLBACK0(EndMemorySection);
   return Result::Ok;
diff --git a/src/binary-writer.cc b/src/binary-writer.cc
index a94eb147..60863d62 100644
--- a/src/binary-writer.cc
+++ b/src/binary-writer.cc
@@ -64,11 +64,18 @@ void WriteType(Stream* stream, Type type, const char* desc) {
   }
 }
 
-void WriteLimits(Stream* stream, const Limits* limits) {
+void WriteLimitsFlags(Stream* stream, uint32_t flags) {
+  WriteU32Leb128(stream, flags, "limits: flags");
+}
+
+uint32_t ComputeLimitsFlags(const Limits* limits) {
   uint32_t flags = limits->has_max ? WABT_BINARY_LIMITS_HAS_MAX_FLAG : 0;
   flags |= limits->is_shared ? WABT_BINARY_LIMITS_IS_SHARED_FLAG : 0;
   flags |= limits->is_64 ? WABT_BINARY_LIMITS_IS_64_FLAG : 0;
-  WriteU32Leb128(stream, flags, "limits: flags");
+  return flags;
+}
+
+void WriteLimitsData(Stream* stream, const Limits* limits) {
   if (limits->is_64) {
     WriteU64Leb128(stream, limits->initial, "limits: initial");
     if (limits->has_max) {
@@ -1157,11 +1164,19 @@ void BinaryWriter::WriteFunc(const Func* func) {
 
 void BinaryWriter::WriteTable(const Table* table) {
   WriteType(stream_, table->elem_type);
-  WriteLimits(stream_, &table->elem_limits);
+  WriteLimitsFlags(stream_, ComputeLimitsFlags(&table->elem_limits));
+  WriteLimitsData(stream_, &table->elem_limits);
 }
 
 void BinaryWriter::WriteMemory(const Memory* memory) {
-  WriteLimits(stream_, &memory->page_limits);
+  uint32_t flags = ComputeLimitsFlags(&memory->page_limits);
+  const bool custom_page_size = memory->page_size != WABT_DEFAULT_PAGE_SIZE;
+  flags |= custom_page_size ? WABT_BINARY_LIMITS_HAS_CUSTOM_PAGE_SIZE_FLAG : 0;
+  WriteLimitsFlags(stream_, flags);
+  WriteLimitsData(stream_, &memory->page_limits);
+  if (custom_page_size) {
+    WriteU32Leb128(stream_, log2_u32(memory->page_size), "memory page size");
+  }
 }
 
 void BinaryWriter::WriteGlobalHeader(const Global* global) {
diff --git a/src/interp/binary-reader-interp.cc b/src/interp/binary-reader-interp.cc
index dc7ec410..1d3daf8e 100644
--- a/src/interp/binary-reader-interp.cc
+++ b/src/interp/binary-reader-interp.cc
@@ -105,7 +105,8 @@ class BinaryReaderInterp : public BinaryReaderNop {
                         std::string_view module_name,
                         std::string_view field_name,
                         Index memory_index,
-                        const Limits* page_limits) override;
+                        const Limits* page_limits,
+                        uint32_t page_size) override;
   Result OnImportGlobal(Index import_index,
                         std::string_view module_name,
                         std::string_view field_name,
@@ -127,7 +128,9 @@ class BinaryReaderInterp : public BinaryReaderNop {
                  const Limits* elem_limits) override;
 
   Result OnMemoryCount(Index count) override;
-  Result OnMemory(Index index, const Limits* limits) override;
+  Result OnMemory(Index index,
+                  const Limits* limits,
+                  uint32_t page_size) override;
 
   Result OnGlobalCount(Index count) override;
   Result BeginGlobal(Index index, Type type, bool mutable_) override;
@@ -537,9 +540,10 @@ Result BinaryReaderInterp::OnImportMemory(Index import_index,
                                           std::string_view module_name,
                                           std::string_view field_name,
                                           Index memory_index,
-                                          const Limits* page_limits) {
-  CHECK_RESULT(validator_.OnMemory(GetLocation(), *page_limits));
-  MemoryType memory_type{*page_limits};
+                                          const Limits* page_limits,
+                                          uint32_t page_size) {
+  CHECK_RESULT(validator_.OnMemory(GetLocation(), *page_limits, page_size));
+  MemoryType memory_type{*page_limits, page_size};
   module_.imports.push_back(ImportDesc{ImportType(
       std::string(module_name), std::string(field_name), memory_type.Clone())});
   memory_types_.push_back(memory_type);
@@ -608,9 +612,11 @@ Result BinaryReaderInterp::OnMemoryCount(Index count) {
   return Result::Ok;
 }
 
-Result BinaryReaderInterp::OnMemory(Index index, const Limits* limits) {
-  CHECK_RESULT(validator_.OnMemory(GetLocation(), *limits));
-  MemoryType memory_type{*limits};
+Result BinaryReaderInterp::OnMemory(Index index,
+                                    const Limits* limits,
+                                    uint32_t page_size) {
+  CHECK_RESULT(validator_.OnMemory(GetLocation(), *limits, page_size));
+  MemoryType memory_type{*limits, page_size};
   module_.memories.push_back(MemoryDesc{memory_type});
   memory_types_.push_back(memory_type);
   return Result::Ok;
diff --git a/src/interp/interp-wasm-c-api.cc b/src/interp/interp-wasm-c-api.cc
index cfa8a897..bb4598a4 100644
--- a/src/interp/interp-wasm-c-api.cc
+++ b/src/interp/interp-wasm-c-api.cc
@@ -160,7 +160,10 @@ struct wasm_tabletype_t : wasm_externtype_t {
 
 struct wasm_memorytype_t : wasm_externtype_t {
   wasm_memorytype_t(const wasm_limits_t* limits)
-      : wasm_externtype_t{std::make_unique<MemoryType>(ToWabtLimits(*limits))},
+      : wasm_externtype_t{std::make_unique<MemoryType>(
+            ToWabtLimits(*limits),
+            WABT_DEFAULT_PAGE_SIZE)},  // wasm-c-api doesn't support
+                                       // custom-page-sizes yet
         limits{*limits} {}
 
   wasm_memorytype_t(MemoryType mt)
diff --git a/src/interp/interp.cc b/src/interp/interp.cc
index a3dd9b4a..f93fa5a6 100644
--- a/src/interp/interp.cc
+++ b/src/interp/interp.cc
@@ -136,6 +136,12 @@ std::unique_ptr<ExternType> MemoryType::Clone() const {
 Result Match(const MemoryType& expected,
              const MemoryType& actual,
              std::string* out_msg) {
+  if (expected.page_size != actual.page_size) {
+    *out_msg = StringPrintf(
+        "page_size mismatch in imported memory, expected %u but got %u.",
+        expected.page_size, actual.page_size);
+    return Result::Error;
+  }
   return Match(expected.limits, actual.limits, out_msg);
 }
 
@@ -576,7 +582,7 @@ Result Table::Copy(Store& store,
 //// Memory ////
 Memory::Memory(class Store&, MemoryType type)
     : Extern(skind), type_(type), pages_(type.limits.initial) {
-  data_.resize(pages_ * WABT_PAGE_SIZE);
+  data_.resize(pages_ * type_.page_size);
 }
 
 void Memory::Mark(class Store&) {}
@@ -597,7 +603,7 @@ Result Memory::Grow(u64 count) {
     auto old_size = data_.size();
 #endif
     pages_ = new_pages;
-    data_.resize(new_pages * WABT_PAGE_SIZE);
+    data_.resize(new_pages * type_.page_size);
 #if WABT_BIG_ENDIAN
     std::move_backward(data_.begin(), data_.begin() + old_size, data_.end());
     std::fill(data_.begin(), data_.end() - old_size, 0);
diff --git a/src/lexer-keywords.txt b/src/lexer-keywords.txt
index e4fd37d3..1c72983b 100644
--- a/src/lexer-keywords.txt
+++ b/src/lexer-keywords.txt
@@ -556,6 +556,7 @@ nan:canonical, TokenType::NanCanonical
 nop, TokenType::Nop, Opcode::Nop
 offset, TokenType::Offset
 output, TokenType::Output
+pagesize, TokenType::PageSize
 param, TokenType::Param
 ref, TokenType::Ref
 quote, TokenType::Quote
diff --git a/src/prebuilt/lexer-keywords.cc b/src/prebuilt/lexer-keywords.cc
index 32b6951a..f04fc537 100644
--- a/src/prebuilt/lexer-keywords.cc
+++ b/src/prebuilt/lexer-keywords.cc
@@ -158,7 +158,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 {
   enum
     {
-      TOTAL_KEYWORDS = 596,
+      TOTAL_KEYWORDS = 597,
       MIN_WORD_LENGTH = 2,
       MAX_WORD_LENGTH = 35,
       MIN_HASH_VALUE = 15,
@@ -224,7 +224,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
       {"f32x4.lt", TokenType::Compare, Opcode::F32X4Lt},
 #line 340 "src/lexer-keywords.txt"
       {"i32x4.lt_u", TokenType::Compare, Opcode::I32X4LtU},
-#line 567 "src/lexer-keywords.txt"
+#line 568 "src/lexer-keywords.txt"
       {"result", TokenType::Result},
 #line 329 "src/lexer-keywords.txt"
       {"i32x4.gt_s", TokenType::Compare, Opcode::I32X4GtS},
@@ -258,10 +258,10 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
       {""},
 #line 107 "src/lexer-keywords.txt"
       {"f32x4.ne", TokenType::Compare, Opcode::F32X4Ne},
-#line 565 "src/lexer-keywords.txt"
+#line 566 "src/lexer-keywords.txt"
       {"ref.null", TokenType::RefNull, Opcode::RefNull},
       {""},
-#line 583 "src/lexer-keywords.txt"
+#line 584 "src/lexer-keywords.txt"
       {"table", TokenType::Table},
 #line 347 "src/lexer-keywords.txt"
       {"i32x4.neg", TokenType::Unary, Opcode::I32X4Neg},
@@ -281,15 +281,15 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
       {""}, {""}, {""}, {""},
 #line 105 "src/lexer-keywords.txt"
       {"f32x4.nearest", TokenType::Unary, Opcode::F32X4Nearest},
-#line 571 "src/lexer-keywords.txt"
+#line 572 "src/lexer-keywords.txt"
       {"return", TokenType::Return, Opcode::Return},
 #line 91 "src/lexer-keywords.txt"
       {"f32x4.ceil", TokenType::Unary, Opcode::F32X4Ceil},
       {""}, {""}, {""},
-#line 578 "src/lexer-keywords.txt"
+#line 579 "src/lexer-keywords.txt"
       {"table.get", TokenType::TableGet, Opcode::TableGet},
       {""},
-#line 581 "src/lexer-keywords.txt"
+#line 582 "src/lexer-keywords.txt"
       {"table.set", TokenType::TableSet, Opcode::TableSet},
       {""},
 #line 141 "src/lexer-keywords.txt"
@@ -297,7 +297,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 80 "src/lexer-keywords.txt"
       {"f32.nearest", TokenType::Unary, Opcode::F32Nearest},
       {""},
-#line 575 "src/lexer-keywords.txt"
+#line 576 "src/lexer-keywords.txt"
       {"struct", Type::Struct, TokenType::Struct},
 #line 147 "src/lexer-keywords.txt"
       {"f64.store", TokenType::Store, Opcode::F64Store},
@@ -348,7 +348,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 346 "src/lexer-keywords.txt"
       {"i32x4.mul", TokenType::Binary, Opcode::I32X4Mul},
       {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""},
-#line 562 "src/lexer-keywords.txt"
+#line 563 "src/lexer-keywords.txt"
       {"ref.extern", TokenType::RefExtern},
       {""}, {""},
 #line 451 "src/lexer-keywords.txt"
@@ -410,7 +410,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 349 "src/lexer-keywords.txt"
       {"i32x4.relaxed_laneselect", TokenType::Ternary, Opcode::I32X4RelaxedLaneSelect},
       {""}, {""}, {""}, {""},
-#line 572 "src/lexer-keywords.txt"
+#line 573 "src/lexer-keywords.txt"
       {"select", TokenType::Select, Opcode::Select},
       {""},
 #line 373 "src/lexer-keywords.txt"
@@ -519,7 +519,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
       {"i64.trunc_f32_s", TokenType::Convert, Opcode::I64TruncF32S},
 #line 310 "src/lexer-keywords.txt"
       {"i32.trunc_f32_s", TokenType::Convert, Opcode::I32TruncF32S},
-#line 566 "src/lexer-keywords.txt"
+#line 567 "src/lexer-keywords.txt"
       {"register", TokenType::Register},
       {""},
 #line 429 "src/lexer-keywords.txt"
@@ -536,7 +536,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 61 "src/lexer-keywords.txt"
       {"f32.ceil", TokenType::Unary, Opcode::F32Ceil},
       {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""},
-#line 582 "src/lexer-keywords.txt"
+#line 583 "src/lexer-keywords.txt"
       {"table.size", TokenType::TableSize, Opcode::TableSize},
 #line 409 "src/lexer-keywords.txt"
       {"i64.atomic.store", TokenType::AtomicStore, Opcode::I64AtomicStore},
@@ -547,7 +547,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 265 "src/lexer-keywords.txt"
       {"i32.atomic.rmw.or", TokenType::AtomicRmw, Opcode::I32AtomicRmwOr},
       {""}, {""}, {""}, {""}, {""},
-#line 570 "src/lexer-keywords.txt"
+#line 571 "src/lexer-keywords.txt"
       {"return_call", TokenType::ReturnCall, Opcode::ReturnCall},
       {""}, {""}, {""}, {""}, {""}, {""},
 #line 389 "src/lexer-keywords.txt"
@@ -583,9 +583,9 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 88 "src/lexer-keywords.txt"
       {"f32", Type::F32},
       {""},
-#line 580 "src/lexer-keywords.txt"
+#line 581 "src/lexer-keywords.txt"
       {"table.init", TokenType::TableInit, Opcode::TableInit},
-#line 586 "src/lexer-keywords.txt"
+#line 587 "src/lexer-keywords.txt"
       {"try", TokenType::Try, Opcode::Try},
       {""}, {""},
 #line 318 "src/lexer-keywords.txt"
@@ -730,7 +730,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
       {""}, {""},
 #line 353 "src/lexer-keywords.txt"
       {"i32x4.shr_u", TokenType::Binary, Opcode::I32X4ShrU},
-#line 564 "src/lexer-keywords.txt"
+#line 565 "src/lexer-keywords.txt"
       {"ref.is_null", TokenType::RefIsNull, Opcode::RefIsNull},
 #line 352 "src/lexer-keywords.txt"
       {"i32x4.shr_s", TokenType::Binary, Opcode::I32X4ShrS},
@@ -756,10 +756,10 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 467 "src/lexer-keywords.txt"
       {"i64x2.mul", TokenType::Binary, Opcode::I64X2Mul},
       {""}, {""}, {""}, {""}, {""}, {""},
-#line 561 "src/lexer-keywords.txt"
+#line 562 "src/lexer-keywords.txt"
       {"quote", TokenType::Quote},
       {""}, {""}, {""}, {""},
-#line 600 "src/lexer-keywords.txt"
+#line 601 "src/lexer-keywords.txt"
       {"v128", Type::V128},
       {""},
 #line 536 "src/lexer-keywords.txt"
@@ -832,7 +832,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
       {"i32x4.relaxed_trunc_f32x4_s", TokenType::Unary, Opcode::I32X4RelaxedTruncF32X4S},
 #line 420 "src/lexer-keywords.txt"
       {"i64.extend_i32_s", TokenType::Convert, Opcode::I64ExtendI32S},
-#line 595 "src/lexer-keywords.txt"
+#line 596 "src/lexer-keywords.txt"
       {"v128.or", TokenType::Binary, Opcode::V128Or},
       {""},
 #line 555 "src/lexer-keywords.txt"
@@ -855,7 +855,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
       {""},
 #line 171 "src/lexer-keywords.txt"
       {"f64x2.relaxed_max", TokenType::Binary, Opcode::F64X2RelaxedMax},
-#line 599 "src/lexer-keywords.txt"
+#line 600 "src/lexer-keywords.txt"
       {"v128.store", TokenType::Store, Opcode::V128Store},
       {""},
 #line 395 "src/lexer-keywords.txt"
@@ -867,7 +867,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
       {""},
 #line 203 "src/lexer-keywords.txt"
       {"i16x8.ge_u", TokenType::Compare, Opcode::I16X8GeU},
-#line 601 "src/lexer-keywords.txt"
+#line 602 "src/lexer-keywords.txt"
       {"v128.xor", TokenType::Binary, Opcode::V128Xor},
 #line 207 "src/lexer-keywords.txt"
       {"i16x8.le_u", TokenType::Compare, Opcode::I16X8LeU},
@@ -895,24 +895,24 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 523 "src/lexer-keywords.txt"
       {"i8x16.relaxed_laneselect", TokenType::Ternary, Opcode::I8X16RelaxedLaneSelect},
       {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""},
-#line 587 "src/lexer-keywords.txt"
+#line 588 "src/lexer-keywords.txt"
       {"type", TokenType::Type},
 #line 404 "src/lexer-keywords.txt"
       {"i64.atomic.rmw.xchg", TokenType::AtomicRmw, Opcode::I64AtomicRmwXchg},
 #line 267 "src/lexer-keywords.txt"
       {"i32.atomic.rmw.xchg", TokenType::AtomicRmw, Opcode::I32AtomicRmwXchg},
       {""},
-#line 594 "src/lexer-keywords.txt"
+#line 595 "src/lexer-keywords.txt"
       {"v128.not", TokenType::Unary, Opcode::V128Not},
       {""}, {""},
-#line 613 "src/lexer-keywords.txt"
+#line 614 "src/lexer-keywords.txt"
       {"v128.store64_lane", TokenType::SimdStoreLane, Opcode::V128Store64Lane},
 #line 219 "src/lexer-keywords.txt"
       {"i16x8.neg", TokenType::Unary, Opcode::I16X8Neg},
       {""},
 #line 221 "src/lexer-keywords.txt"
       {"i16x8.ne", TokenType::Compare, Opcode::I16X8Ne},
-#line 606 "src/lexer-keywords.txt"
+#line 607 "src/lexer-keywords.txt"
       {"v128.load8_lane", TokenType::SimdLoadLane, Opcode::V128Load8Lane},
 #line 466 "src/lexer-keywords.txt"
       {"v128.load32x2_u", TokenType::Load, Opcode::V128Load32X2U},
@@ -934,9 +934,9 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 535 "src/lexer-keywords.txt"
       {"input", TokenType::Input},
       {""}, {""},
-#line 593 "src/lexer-keywords.txt"
+#line 594 "src/lexer-keywords.txt"
       {"v128.load", TokenType::Load, Opcode::V128Load},
-#line 605 "src/lexer-keywords.txt"
+#line 606 "src/lexer-keywords.txt"
       {"v128.load8_splat", TokenType::Load, Opcode::V128Load8Splat},
       {""},
 #line 534 "src/lexer-keywords.txt"
@@ -956,7 +956,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
       {""}, {""},
 #line 116 "src/lexer-keywords.txt"
       {"f32x4.sqrt", TokenType::Unary, Opcode::F32X4Sqrt},
-#line 569 "src/lexer-keywords.txt"
+#line 570 "src/lexer-keywords.txt"
       {"return_call_indirect", TokenType::ReturnCallIndirect, Opcode::ReturnCallIndirect},
       {""}, {""}, {""}, {""}, {""}, {""},
 #line 397 "src/lexer-keywords.txt"
@@ -972,7 +972,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 108 "src/lexer-keywords.txt"
       {"f32x4.pmax", TokenType::Binary, Opcode::F32X4PMax},
       {""}, {""}, {""}, {""},
-#line 592 "src/lexer-keywords.txt"
+#line 593 "src/lexer-keywords.txt"
       {"v128.const", TokenType::Const, Opcode::V128Const},
 #line 173 "src/lexer-keywords.txt"
       {"f64x2.relaxed_nmadd", TokenType::Ternary, Opcode::F64X2RelaxedNmadd},
@@ -980,11 +980,11 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 525 "src/lexer-keywords.txt"
       {"i8x16.shl", TokenType::Binary, Opcode::I8X16Shl},
       {""},
-#line 590 "src/lexer-keywords.txt"
+#line 591 "src/lexer-keywords.txt"
       {"v128.and", TokenType::Binary, Opcode::V128And},
 #line 533 "src/lexer-keywords.txt"
       {"if", TokenType::If, Opcode::If},
-#line 560 "src/lexer-keywords.txt"
+#line 561 "src/lexer-keywords.txt"
       {"ref", TokenType::Ref},
       {""}, {""}, {""},
 #line 551 "src/lexer-keywords.txt"
@@ -995,7 +995,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 216 "src/lexer-keywords.txt"
       {"i16x8.mul", TokenType::Binary, Opcode::I16X8Mul},
       {""}, {""}, {""}, {""},
-#line 589 "src/lexer-keywords.txt"
+#line 590 "src/lexer-keywords.txt"
       {"v128.andnot", TokenType::Binary, Opcode::V128Andnot},
 #line 51 "src/lexer-keywords.txt"
       {"else", TokenType::Else, Opcode::Else},
@@ -1013,10 +1013,10 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 224 "src/lexer-keywords.txt"
       {"i16x8.replace_lane", TokenType::SimdLaneOp, Opcode::I16X8ReplaceLane},
       {""}, {""}, {""}, {""}, {""}, {""},
-#line 584 "src/lexer-keywords.txt"
+#line 585 "src/lexer-keywords.txt"
       {"then", TokenType::Then},
       {""},
-#line 611 "src/lexer-keywords.txt"
+#line 612 "src/lexer-keywords.txt"
       {"v128.store16_lane", TokenType::SimdStoreLane, Opcode::V128Store16Lane},
       {""}, {""}, {""}, {""},
 #line 163 "src/lexer-keywords.txt"
@@ -1087,7 +1087,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 230 "src/lexer-keywords.txt"
       {"i16x8.sub_sat_u", TokenType::Binary, Opcode::I16X8SubSatU},
       {""},
-#line 576 "src/lexer-keywords.txt"
+#line 577 "src/lexer-keywords.txt"
       {"table.copy", TokenType::TableCopy, Opcode::TableCopy},
       {""},
 #line 229 "src/lexer-keywords.txt"
@@ -1096,7 +1096,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 522 "src/lexer-keywords.txt"
       {"i8x16.relaxed_swizzle", TokenType::Binary, Opcode::I8X16RelaxedSwizzle},
       {""}, {""},
-#line 603 "src/lexer-keywords.txt"
+#line 604 "src/lexer-keywords.txt"
       {"v128.load32_splat", TokenType::Load, Opcode::V128Load32Splat},
       {""}, {""}, {""}, {""}, {""},
 #line 486 "src/lexer-keywords.txt"
@@ -1104,13 +1104,13 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
       {""},
 #line 485 "src/lexer-keywords.txt"
       {"i64x2.shr_s", TokenType::Binary, Opcode::I64X2ShrS},
-#line 610 "src/lexer-keywords.txt"
+#line 611 "src/lexer-keywords.txt"
       {"v128.store8_lane", TokenType::SimdStoreLane, Opcode::V128Store8Lane},
       {""},
 #line 183 "src/lexer-keywords.txt"
       {"field", TokenType::Field},
       {""},
-#line 608 "src/lexer-keywords.txt"
+#line 609 "src/lexer-keywords.txt"
       {"v128.load32_lane", TokenType::SimdLoadLane, Opcode::V128Load32Lane},
       {""}, {""},
 #line 21 "src/lexer-keywords.txt"
@@ -1122,7 +1122,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
       {"f64.floor", TokenType::Unary, Opcode::F64Floor},
 #line 71 "src/lexer-keywords.txt"
       {"f32.floor", TokenType::Unary, Opcode::F32Floor},
-#line 559 "src/lexer-keywords.txt"
+#line 560 "src/lexer-keywords.txt"
       {"param", TokenType::Param},
       {""},
 #line 549 "src/lexer-keywords.txt"
@@ -1131,19 +1131,19 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 117 "src/lexer-keywords.txt"
       {"f32x4.sub", TokenType::Binary, Opcode::F32X4Sub},
       {""}, {""}, {""}, {""},
-#line 597 "src/lexer-keywords.txt"
+#line 598 "src/lexer-keywords.txt"
       {"v128.load32_zero", TokenType::Load, Opcode::V128Load32Zero},
 #line 355 "src/lexer-keywords.txt"
       {"i32x4.sub", TokenType::Binary, Opcode::I32X4Sub},
       {""}, {""}, {""},
-#line 563 "src/lexer-keywords.txt"
+#line 564 "src/lexer-keywords.txt"
       {"ref.func", TokenType::RefFunc, Opcode::RefFunc},
       {""},
 #line 121 "src/lexer-keywords.txt"
       {"f64.abs", TokenType::Unary, Opcode::F64Abs},
 #line 59 "src/lexer-keywords.txt"
       {"f32.abs", TokenType::Unary, Opcode::F32Abs},
-#line 574 "src/lexer-keywords.txt"
+#line 575 "src/lexer-keywords.txt"
       {"start", TokenType::Start},
 #line 449 "src/lexer-keywords.txt"
       {"i64.store16", TokenType::Store, Opcode::I64Store16},
@@ -1161,7 +1161,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 526 "src/lexer-keywords.txt"
       {"i8x16.shr_s", TokenType::Binary, Opcode::I8X16ShrS},
       {""}, {""}, {""},
-#line 596 "src/lexer-keywords.txt"
+#line 597 "src/lexer-keywords.txt"
       {"v128.any_true", TokenType::Unary, Opcode::V128AnyTrue},
       {""}, {""}, {""}, {""}, {""}, {""},
 #line 193 "src/lexer-keywords.txt"
@@ -1182,7 +1182,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
       {"i16x8.max_s", TokenType::Binary, Opcode::I16X8MaxS},
       {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""},
       {""}, {""}, {""}, {""},
-#line 604 "src/lexer-keywords.txt"
+#line 605 "src/lexer-keywords.txt"
       {"v128.load64_splat", TokenType::Load, Opcode::V128Load64Splat},
       {""}, {""}, {""},
 #line 375 "src/lexer-keywords.txt"
@@ -1190,7 +1190,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 34 "src/lexer-keywords.txt"
       {"br_table", TokenType::BrTable, Opcode::BrTable},
       {""}, {""}, {""}, {""}, {""}, {""}, {""},
-#line 609 "src/lexer-keywords.txt"
+#line 610 "src/lexer-keywords.txt"
       {"v128.load64_lane", TokenType::SimdLoadLane, Opcode::V128Load64Lane},
 #line 94 "src/lexer-keywords.txt"
       {"f32x4.div", TokenType::Binary, Opcode::F32X4Div},
@@ -1217,10 +1217,10 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 528 "src/lexer-keywords.txt"
       {"i8x16.splat", TokenType::Unary, Opcode::I8X16Splat},
       {""}, {""},
-#line 598 "src/lexer-keywords.txt"
+#line 599 "src/lexer-keywords.txt"
       {"v128.load64_zero", TokenType::Load, Opcode::V128Load64Zero},
       {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""},
-#line 585 "src/lexer-keywords.txt"
+#line 586 "src/lexer-keywords.txt"
       {"throw", TokenType::Throw, Opcode::Throw},
       {""},
 #line 68 "src/lexer-keywords.txt"
@@ -1234,15 +1234,15 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 47 "src/lexer-keywords.txt"
       {"drop", TokenType::Drop, Opcode::Drop},
       {""}, {""}, {""},
-#line 612 "src/lexer-keywords.txt"
+#line 613 "src/lexer-keywords.txt"
       {"v128.store32_lane", TokenType::SimdStoreLane, Opcode::V128Store32Lane},
       {""}, {""}, {""}, {""}, {""},
-#line 573 "src/lexer-keywords.txt"
+#line 574 "src/lexer-keywords.txt"
       {"shared", TokenType::Shared},
-#line 615 "src/lexer-keywords.txt"
+#line 616 "src/lexer-keywords.txt"
       {"i8x16.swizzle", TokenType::Binary, Opcode::I8X16Swizzle},
       {""}, {""}, {""}, {""},
-#line 577 "src/lexer-keywords.txt"
+#line 578 "src/lexer-keywords.txt"
       {"table.fill", TokenType::TableFill, Opcode::TableFill},
       {""}, {""}, {""}, {""}, {""}, {""},
 #line 394 "src/lexer-keywords.txt"
@@ -1252,7 +1252,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 119 "src/lexer-keywords.txt"
       {"f32x4.demote_f64x2_zero", TokenType::Unary, Opcode::F32X4DemoteF64X2Zero},
       {""}, {""}, {""},
-#line 588 "src/lexer-keywords.txt"
+#line 589 "src/lexer-keywords.txt"
       {"unreachable", TokenType::Unreachable, Opcode::Unreachable},
       {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""},
       {""}, {""}, {""}, {""}, {""},
@@ -1286,10 +1286,10 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 251 "src/lexer-keywords.txt"
       {"i32.atomic.rmw16.or_u", TokenType::AtomicRmw, Opcode::I32AtomicRmw16OrU},
       {""}, {""}, {""}, {""}, {""}, {""},
-#line 568 "src/lexer-keywords.txt"
+#line 569 "src/lexer-keywords.txt"
       {"rethrow", TokenType::Rethrow, Opcode::Rethrow},
       {""}, {""}, {""},
-#line 579 "src/lexer-keywords.txt"
+#line 580 "src/lexer-keywords.txt"
       {"table.grow", TokenType::TableGrow, Opcode::TableGrow},
 #line 345 "src/lexer-keywords.txt"
       {"i32x4.dot_i16x8_s", TokenType::Binary, Opcode::I32X4DotI16X8S},
@@ -1375,8 +1375,10 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 297 "src/lexer-keywords.txt"
       {"i32.popcnt", TokenType::Unary, Opcode::I32Popcnt},
       {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""},
-      {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""},
-      {""}, {""},
+      {""}, {""}, {""}, {""},
+#line 559 "src/lexer-keywords.txt"
+      {"pagesize", TokenType::PageSize},
+      {""}, {""}, {""}, {""}, {""}, {""},
 #line 556 "src/lexer-keywords.txt"
       {"nop", TokenType::Nop, Opcode::Nop},
       {""}, {""},
@@ -1520,7 +1522,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 479 "src/lexer-keywords.txt"
       {"i64x2.extend_high_i32x4_s", TokenType::Unary, Opcode::I64X2ExtendHighI32X4S},
       {""},
-#line 614 "src/lexer-keywords.txt"
+#line 615 "src/lexer-keywords.txt"
       {"i8x16.shuffle", TokenType::SimdShuffleOp, Opcode::I8X16Shuffle},
 #line 380 "src/lexer-keywords.txt"
       {"i64.atomic.rmw16.cmpxchg_u", TokenType::AtomicRmwCmpxchg, Opcode::I64AtomicRmw16CmpxchgU},
@@ -1567,7 +1569,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 184 "src/lexer-keywords.txt"
       {"funcref", Type::FuncRef},
       {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""},
-#line 602 "src/lexer-keywords.txt"
+#line 603 "src/lexer-keywords.txt"
       {"v128.load16_splat", TokenType::Load, Opcode::V128Load16Splat},
       {""}, {""}, {""}, {""}, {""},
 #line 368 "src/lexer-keywords.txt"
@@ -1576,7 +1578,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 367 "src/lexer-keywords.txt"
       {"i32x4.extend_low_i16x8_s", TokenType::Unary, Opcode::I32X4ExtendLowI16X8S},
       {""}, {""}, {""}, {""},
-#line 607 "src/lexer-keywords.txt"
+#line 608 "src/lexer-keywords.txt"
       {"v128.load16_lane", TokenType::SimdLoadLane, Opcode::V128Load16Lane},
       {""}, {""}, {""}, {""}, {""}, {""},
 #line 50 "src/lexer-keywords.txt"
@@ -1617,7 +1619,7 @@ Perfect_Hash::InWordSet (const char *str, size_t len)
 #line 27 "src/lexer-keywords.txt"
       {"assert_trap", TokenType::AssertTrap},
       {""}, {""}, {""}, {""},
-#line 591 "src/lexer-keywords.txt"
+#line 592 "src/lexer-keywords.txt"
       {"v128.bitselect", TokenType::Ternary, Opcode::V128BitSelect},
       {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""},
       {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""}, {""},
diff --git a/src/shared-validator.cc b/src/shared-validator.cc
index 914b5346..6492cbeb 100644
--- a/src/shared-validator.cc
+++ b/src/shared-validator.cc
@@ -134,13 +134,25 @@ Result SharedValidator::OnTable(const Location& loc,
   return result;
 }
 
-Result SharedValidator::OnMemory(const Location& loc, const Limits& limits) {
+Result SharedValidator::OnMemory(const Location& loc,
+                                 const Limits& limits,
+                                 uint32_t page_size) {
   Result result = Result::Ok;
   if (memories_.size() > 0 && !options_.features.multi_memory_enabled()) {
     result |= PrintError(loc, "only one memory block allowed");
   }
-  result |= CheckLimits(
-      loc, limits, limits.is_64 ? WABT_MAX_PAGES64 : WABT_MAX_PAGES32, "pages");
+
+  if (page_size != WABT_DEFAULT_PAGE_SIZE) {
+    if (!options_.features.custom_page_sizes_enabled()) {
+      result |= PrintError(loc, "only default page size (64 KiB) is allowed");
+    } else if (page_size != 1) {
+      result |= PrintError(loc, "only page sizes of 1 B or 64 KiB are allowed");
+    }
+  }
+
+  uint64_t absolute_max = WABT_BYTES_TO_MIN_PAGES(
+      (limits.is_64 ? UINT64_MAX : UINT32_MAX), page_size);
+  result |= CheckLimits(loc, limits, absolute_max, "pages");
 
   if (limits.is_shared) {
     if (!options_.features.threads_enabled()) {
diff --git a/src/test-interp.cc b/src/test-interp.cc
index 614eed33..9346b7b1 100644
--- a/src/test-interp.cc
+++ b/src/test-interp.cc
@@ -491,7 +491,8 @@ TEST_F(InterpTest, Rot13) {
 
   std::string string_data = "Hello, WebAssembly!";
 
-  auto memory = Memory::New(store_, MemoryType{Limits{1}});
+  auto memory =
+      Memory::New(store_, MemoryType{Limits{1}, WABT_DEFAULT_PAGE_SIZE});
 
   auto fill_buf = [&](Thread& thread, const Values& params, Values& results,
                       Trap::Ptr* out_trap) -> Result {
@@ -659,7 +660,7 @@ TEST_F(InterpGCTest, Collect_InstanceImport) {
                          [](Thread& thread, const Values&, Values&,
                             Trap::Ptr*) -> Result { return Result::Ok; });
   auto t = Table::New(store_, TableType{ValueType::FuncRef, Limits{0}});
-  auto m = Memory::New(store_, MemoryType{Limits{0}});
+  auto m = Memory::New(store_, MemoryType{Limits{0}, WABT_DEFAULT_PAGE_SIZE});
   auto g = Global::New(store_, GlobalType{ValueType::I32, Mutability::Const},
                        Value::Make(5));
 
diff --git a/src/tools/spectest-interp.cc b/src/tools/spectest-interp.cc
index 2dd4202b..d859f148 100644
--- a/src/tools/spectest-interp.cc
+++ b/src/tools/spectest-interp.cc
@@ -1313,7 +1313,8 @@ CommandRunner::CommandRunner() : store_(s_features) {
   spectest["table64"] = interp::Table::New(
       store_, TableType{ValueType::FuncRef, Limits{10, 20, false, true}});
 
-  spectest["memory"] = interp::Memory::New(store_, MemoryType{Limits{1, 2}});
+  spectest["memory"] = interp::Memory::New(
+      store_, MemoryType{Limits{1, 2}, WABT_DEFAULT_PAGE_SIZE});
 
   spectest["global_i32"] =
       interp::Global::New(store_, GlobalType{ValueType::I32, Mutability::Const},
diff --git a/src/validator.cc b/src/validator.cc
index 980618c8..71c78411 100644
--- a/src/validator.cc
+++ b/src/validator.cc
@@ -732,7 +732,8 @@ Result Validator::CheckModule() {
 
         case ExternalKind::Memory: {
           auto&& memory = cast<MemoryImport>(f->import.get())->memory;
-          result_ |= validator_.OnMemory(field.loc, memory.page_limits);
+          result_ |= validator_.OnMemory(field.loc, memory.page_limits,
+                                         memory.page_size);
           break;
         }
 
@@ -772,7 +773,8 @@ Result Validator::CheckModule() {
   // Memory section.
   for (const ModuleField& field : module->fields) {
     if (auto* f = dyn_cast<MemoryModuleField>(&field)) {
-      result_ |= validator_.OnMemory(field.loc, f->memory.page_limits);
+      result_ |= validator_.OnMemory(field.loc, f->memory.page_limits,
+                                     f->memory.page_size);
     }
   }
 
diff --git a/src/wast-parser.cc b/src/wast-parser.cc
index eb67dceb..e3606b7c 100644
--- a/src/wast-parser.cc
+++ b/src/wast-parser.cc
@@ -1146,6 +1146,37 @@ Result WastParser::ParseLimits(Limits* out_limits) {
   return Result::Ok;
 }
 
+Result WastParser::ParsePageSize(uint32_t* out_page_size) {
+  WABT_TRACE(ParsePageSize);
+
+  Result result = Result::Ok;
+
+  if (PeekMatchLpar(TokenType::PageSize)) {
+    if (!options_->features.custom_page_sizes_enabled()) {
+      Error(GetLocation(), "Specifying memory page size is not allowed");
+      return Result::Error;
+    }
+    EXPECT(Lpar);
+    EXPECT(PageSize);
+    auto token = GetToken();
+    if (!token.HasLiteral()) {
+      Error(GetLocation(), "malformed custom page size");
+      return Result::Error;
+    }
+    auto sv = token.literal().text;
+    result |= ParseInt32(sv, out_page_size, ParseIntType::UnsignedOnly);
+    if (*out_page_size > UINT32_MAX || *out_page_size <= 0 ||
+        (*out_page_size & (*out_page_size - 1))) {
+      Error(GetLocation(), "malformed custom page size");
+      return Result::Error;
+    }
+    Consume();
+    EXPECT(Rpar);
+  }
+
+  return result;
+}
+
 Result WastParser::ParseNat(uint64_t* out_nat, bool is_64) {
   WABT_TRACE(ParseNat);
   if (!PeekMatch(TokenType::Nat)) {
@@ -1674,8 +1705,10 @@ Result WastParser::ParseImportModuleField(Module* module) {
       Consume();
       ParseBindVarOpt(&name);
       auto import = std::make_unique<MemoryImport>(name);
+      import->memory.page_size = WABT_DEFAULT_PAGE_SIZE;
       CHECK_RESULT(ParseLimitsIndex(&import->memory.page_limits));
       CHECK_RESULT(ParseLimits(&import->memory.page_limits));
+      CHECK_RESULT(ParsePageSize(&import->memory.page_size));
       EXPECT(Rpar);
       field = std::make_unique<ImportModuleField>(std::move(import), loc);
       break;
@@ -1728,15 +1761,26 @@ Result WastParser::ParseMemoryModuleField(Module* module) {
   if (PeekMatchLpar(TokenType::Import)) {
     CheckImportOrdering(module);
     auto import = std::make_unique<MemoryImport>(name);
+    import->memory.page_size = WABT_DEFAULT_PAGE_SIZE;
     CHECK_RESULT(ParseInlineImport(import.get()));
     CHECK_RESULT(ParseLimitsIndex(&import->memory.page_limits));
     CHECK_RESULT(ParseLimits(&import->memory.page_limits));
+    CHECK_RESULT(ParsePageSize(&import->memory.page_size));
     auto field =
         std::make_unique<ImportModuleField>(std::move(import), GetLocation());
     module->AppendField(std::move(field));
   } else {
     auto field = std::make_unique<MemoryModuleField>(loc, name);
+    field->memory.page_size = WABT_DEFAULT_PAGE_SIZE;
     CHECK_RESULT(ParseLimitsIndex(&field->memory.page_limits));
+    if (PeekMatchLpar(TokenType::PageSize)) {
+      // this is the data abbreviation (no limits)
+      CHECK_RESULT(ParsePageSize(&field->memory.page_size));
+      if (!PeekMatchLpar(TokenType::Data)) {
+        ConsumeIfLpar();
+        return ErrorExpected({"inline data segment"});
+      }
+    }
     if (MatchLpar(TokenType::Data)) {
       auto data_segment_field = std::make_unique<DataSegmentModuleField>(loc);
       DataSegment& data_segment = data_segment_field->data_segment;
@@ -1747,16 +1791,17 @@ Result WastParser::ParseMemoryModuleField(Module* module) {
       ParseTextListOpt(&data_segment.data);
       EXPECT(Rpar);
 
-      uint32_t byte_size = WABT_ALIGN_UP_TO_PAGE(data_segment.data.size());
-      uint32_t page_size = WABT_BYTES_TO_PAGES(byte_size);
-      field->memory.page_limits.initial = page_size;
-      field->memory.page_limits.max = page_size;
+      uint32_t num_pages = WABT_BYTES_TO_MIN_PAGES(data_segment.data.size(),
+                                                   field->memory.page_size);
+      field->memory.page_limits.initial = num_pages;
+      field->memory.page_limits.max = num_pages;
       field->memory.page_limits.has_max = true;
 
       module->AppendField(std::move(field));
       module->AppendField(std::move(data_segment_field));
     } else {
       CHECK_RESULT(ParseLimits(&field->memory.page_limits));
+      CHECK_RESULT(ParsePageSize(&field->memory.page_size));
       module->AppendField(std::move(field));
     }
   }
diff --git a/src/wat-writer.cc b/src/wat-writer.cc
index b458eca1..a013717a 100644
--- a/src/wat-writer.cc
+++ b/src/wat-writer.cc
@@ -1496,6 +1496,11 @@ void WatWriter::WriteMemory(const Memory& memory) {
   WriteInlineExports(ExternalKind::Memory, memory_index_);
   WriteInlineImport(ExternalKind::Memory, memory_index_);
   WriteLimits(memory.page_limits);
+  if (memory.page_size != WABT_DEFAULT_PAGE_SIZE) {
+    WriteOpenSpace("pagesize");
+    Writef("%u", memory.page_size);
+    WriteCloseSpace();
+  }
   WriteCloseNewline();
   memory_index_++;
 }
diff --git a/test/binary/bad-memory-limits-flag.txt b/test/binary/bad-memory-limits-flag.txt
index 3e8922b8..7c413f59 100644
--- a/test/binary/bad-memory-limits-flag.txt
+++ b/test/binary/bad-memory-limits-flag.txt
@@ -3,9 +3,9 @@ magic
 version
 section(MEMORY) {
   count[1]
-  flags[8]
+  flags[16]
 }
 (;; STDERR ;;;
-000000c: error: malformed memory limits flag: 8
-000000c: error: malformed memory limits flag: 8
+000000c: error: malformed memory limits flag: 16
+000000c: error: malformed memory limits flag: 16
 ;;; STDERR ;;)
diff --git a/test/help/spectest-interp.txt b/test/help/spectest-interp.txt
index 0bbeb97b..3fc0e6d7 100644
--- a/test/help/spectest-interp.txt
+++ b/test/help/spectest-interp.txt
@@ -31,6 +31,7 @@ options:
       --enable-multi-memory                    Enable Multi-memory
       --enable-extended-const                  Enable Extended constant expressions
       --enable-relaxed-simd                    Enable Relaxed SIMD
+      --enable-custom-page-sizes               Enable Custom page sizes
       --enable-all                             Enable all features
   -V, --value-stack-size=SIZE                  Size in elements of the value stack
   -C, --call-stack-size=SIZE                   Size in elements of the call stack
diff --git a/test/help/wasm-interp.txt b/test/help/wasm-interp.txt
index f0199d0a..800532e6 100644
--- a/test/help/wasm-interp.txt
+++ b/test/help/wasm-interp.txt
@@ -45,6 +45,7 @@ options:
       --enable-multi-memory                    Enable Multi-memory
       --enable-extended-const                  Enable Extended constant expressions
       --enable-relaxed-simd                    Enable Relaxed SIMD
+      --enable-custom-page-sizes               Enable Custom page sizes
       --enable-all                             Enable all features
   -V, --value-stack-size=SIZE                  Size in elements of the value stack
   -C, --call-stack-size=SIZE                   Size in elements of the call stack
diff --git a/test/help/wasm-stats.txt b/test/help/wasm-stats.txt
index fb3b7583..5e83b1e3 100644
--- a/test/help/wasm-stats.txt
+++ b/test/help/wasm-stats.txt
@@ -31,6 +31,7 @@ options:
       --enable-multi-memory                    Enable Multi-memory
       --enable-extended-const                  Enable Extended constant expressions
       --enable-relaxed-simd                    Enable Relaxed SIMD
+      --enable-custom-page-sizes               Enable Custom page sizes
       --enable-all                             Enable all features
   -o, --output=FILENAME                        Output file for the stats, by default use stdout
   -c, --cutoff=N                               Cutoff for reporting counts less than N
diff --git a/test/help/wasm-validate.txt b/test/help/wasm-validate.txt
index 8e3de11b..1b4b424b 100644
--- a/test/help/wasm-validate.txt
+++ b/test/help/wasm-validate.txt
@@ -31,6 +31,7 @@ options:
       --enable-multi-memory                    Enable Multi-memory
       --enable-extended-const                  Enable Extended constant expressions
       --enable-relaxed-simd                    Enable Relaxed SIMD
+      --enable-custom-page-sizes               Enable Custom page sizes
       --enable-all                             Enable all features
       --no-debug-names                         Ignore debug names in the binary file
       --ignore-custom-section-errors           Ignore errors in custom sections
diff --git a/test/help/wasm2wat.txt b/test/help/wasm2wat.txt
index 39f7ae35..f2b2f5c8 100644
--- a/test/help/wasm2wat.txt
+++ b/test/help/wasm2wat.txt
@@ -37,6 +37,7 @@ options:
       --enable-multi-memory                    Enable Multi-memory
       --enable-extended-const                  Enable Extended constant expressions
       --enable-relaxed-simd                    Enable Relaxed SIMD
+      --enable-custom-page-sizes               Enable Custom page sizes
       --enable-all                             Enable all features
       --inline-exports                         Write all exports inline
       --inline-imports                         Write all imports inline
diff --git a/test/help/wast2json.txt b/test/help/wast2json.txt
index d6888fc2..1dbb9c54 100644
--- a/test/help/wast2json.txt
+++ b/test/help/wast2json.txt
@@ -34,6 +34,7 @@ options:
       --enable-multi-memory                    Enable Multi-memory
       --enable-extended-const                  Enable Extended constant expressions
       --enable-relaxed-simd                    Enable Relaxed SIMD
+      --enable-custom-page-sizes               Enable Custom page sizes
       --enable-all                             Enable all features
   -o, --output=FILE                            output JSON file
   -r, --relocatable                            Create a relocatable wasm binary (suitable for linking with e.g. lld)
diff --git a/test/help/wat-desugar.txt b/test/help/wat-desugar.txt
index 5d84034f..2560ed75 100644
--- a/test/help/wat-desugar.txt
+++ b/test/help/wat-desugar.txt
@@ -41,6 +41,7 @@ options:
       --enable-multi-memory                    Enable Multi-memory
       --enable-extended-const                  Enable Extended constant expressions
       --enable-relaxed-simd                    Enable Relaxed SIMD
+      --enable-custom-page-sizes               Enable Custom page sizes
       --enable-all                             Enable all features
       --generate-names                         Give auto-generated names to non-named functions, types, etc.
 ;;; STDOUT ;;)
diff --git a/test/help/wat2wasm.txt b/test/help/wat2wasm.txt
index 31ca9714..19b3d5d1 100644
--- a/test/help/wat2wasm.txt
+++ b/test/help/wat2wasm.txt
@@ -41,6 +41,7 @@ options:
       --enable-multi-memory                    Enable Multi-memory
       --enable-extended-const                  Enable Extended constant expressions
       --enable-relaxed-simd                    Enable Relaxed SIMD
+      --enable-custom-page-sizes               Enable Custom page sizes
       --enable-all                             Enable all features
   -o, --output=FILE                            Output wasm binary file. Use "-" to write to stdout.
   -r, --relocatable                            Create a relocatable wasm binary (suitable for linking with e.g. lld)
diff --git a/test/interp/custom-page-sizes.txt b/test/interp/custom-page-sizes.txt
new file mode 100644
index 00000000..2f1692ca
--- /dev/null
+++ b/test/interp/custom-page-sizes.txt
@@ -0,0 +1,131 @@
+;;; TOOL: run-interp-spec
+;;; ARGS*: --enable-custom-page-sizes --enable-memory64
+
+;; Page size of zero is malformed
+(assert_malformed
+  (module quote "(memory 0 (pagesize 0))")
+  "invalid custom page size")
+
+;; Maximum memory sizes with pagesize 1 and 65536
+;; These are valid but would instantiate a huge memory,
+;; so test with `assert_unlinkable`.
+
+;; i32 (pagesize 1)
+(assert_unlinkable
+  (module
+    (import "test" "unknown" (func))
+    (memory 0xFFFF_FFFF (pagesize 1)))
+  "unknown import")
+
+;; i64 (pagesize 1)
+(assert_unlinkable
+  (module
+    (import "test" "import" (func))
+    (memory i64 0xFFFF_FFFF_FFFF_FFFF (pagesize 1)))
+  "unknown import")
+
+;; i32 (default pagesize)
+(assert_unlinkable
+  (module
+    (import "test" "unknown" (func))
+    (memory 65536 (pagesize 65536)))
+  "unknown import")
+
+;; i64 (default pagesize)
+(assert_unlinkable
+  (module
+    (import "test" "unknown" (func))
+    (memory i64 0x1_0000_0000_0000 (pagesize 65536)))
+  "unknown import")
+
+;; Memory size just over the maximum.
+;;
+;; These are malformed (for pagesize 1)
+;; or invalid (for other pagesizes).
+
+;; i32 (pagesize 1)
+(assert_malformed
+  (module quote "(memory 0x1_0000_0000 (pagesize 1))")
+  "constant out of range")
+
+;; i64 (pagesize 1)
+(assert_malformed
+  (module quote "(memory i64 0x1_0000_0000_0000_0000 (pagesize 1))")
+  "constant out of range")
+
+;; i32 (default pagesize)
+(assert_invalid
+  (module
+    (memory 65537 (pagesize 65536)))
+  "memory size must be at most")
+
+;; i64 (default pagesize)
+(assert_invalid
+  (module
+    (memory i64 0x1_0000_0000_0001 (pagesize 65536)))
+  "memory size must be at most")
+
+;; Test data abbreviation syntax
+
+(assert_malformed (module quote "(memory (pagesize 0) (data))") "invalid custom page size")
+
+(module
+  (memory (pagesize 1) (data "xyz"))
+  (func (export "size") (result i32)
+    memory.size)
+  (func (export "grow") (param i32) (result i32)
+    (memory.grow (local.get 0)))
+  (func (export "load") (param i32) (result i32)
+    (i32.load8_u (local.get 0))))
+
+(assert_return (invoke "size") (i32.const 3))
+(assert_return (invoke "load" (i32.const 0)) (i32.const 120))
+(assert_return (invoke "load" (i32.const 1)) (i32.const 121))
+(assert_return (invoke "load" (i32.const 2)) (i32.const 122))
+(assert_trap (invoke "load" (i32.const 3)) "out of bounds")
+(assert_return (invoke "grow" (i32.const 1)) (i32.const -1))
+
+(module
+  (memory (pagesize 65536) (data "xyz"))
+  (func (export "size") (result i32)
+        memory.size))
+
+(assert_return (invoke "size") (i32.const 1))
+
+(;; STDOUT ;;;
+out/test/interp/custom-page-sizes.txt:6: assert_malformed passed:
+  out/test/interp/custom-page-sizes/custom-page-sizes.0.wat:1:21: error: malformed custom page size
+  (memory 0 (pagesize 0))
+                      ^
+out/test/interp/custom-page-sizes.txt:15: assert_unlinkable passed:
+  error: invalid import "test.unknown"
+out/test/interp/custom-page-sizes.txt:22: assert_unlinkable passed:
+  error: invalid import "test.import"
+out/test/interp/custom-page-sizes.txt:29: assert_unlinkable passed:
+  error: invalid import "test.unknown"
+out/test/interp/custom-page-sizes.txt:36: assert_unlinkable passed:
+  error: invalid import "test.unknown"
+out/test/interp/custom-page-sizes.txt:48: assert_malformed passed:
+  out/test/interp/custom-page-sizes/custom-page-sizes.5.wat:1:9: error: invalid int "0x1_0000_0000"
+  (memory 0x1_0000_0000 (pagesize 1))
+          ^^^^^^^^^^^^^
+out/test/interp/custom-page-sizes.txt:53: assert_malformed passed:
+  out/test/interp/custom-page-sizes/custom-page-sizes.6.wat:1:13: error: invalid int "0x1_0000_0000_0000_0000"
+  (memory i64 0x1_0000_0000_0000_0000 (pagesize 1))
+              ^^^^^^^^^^^^^^^^^^^^^^^
+out/test/interp/custom-page-sizes.txt:58: assert_invalid passed:
+  out/test/interp/custom-page-sizes/custom-page-sizes.7.wasm:000000f: error: initial pages (65537) must be <= (65536)
+  000000f: error: OnMemory callback failed
+out/test/interp/custom-page-sizes.txt:64: assert_invalid passed:
+  out/test/interp/custom-page-sizes/custom-page-sizes.8.wasm:0000013: error: initial pages (281474976710657) must be <= (281474976710656)
+  0000013: error: OnMemory callback failed
+out/test/interp/custom-page-sizes.txt:70: assert_malformed passed:
+  out/test/interp/custom-page-sizes/custom-page-sizes.9.wat:1:19: error: malformed custom page size
+  (memory (pagesize 0) (data))
+                    ^
+  out/test/interp/custom-page-sizes/custom-page-sizes.9.wat:1:28: error: unexpected token ), expected EOF.
+  (memory (pagesize 0) (data))
+                             ^
+out/test/interp/custom-page-sizes.txt:85: assert_trap passed: out of bounds memory access: access at 3+1 >= max value 3
+19/19 tests passed.
+;;; STDOUT ;;)
diff --git a/test/roundtrip/custom-page-sizes.txt b/test/roundtrip/custom-page-sizes.txt
new file mode 100644
index 00000000..8aef1316
--- /dev/null
+++ b/test/roundtrip/custom-page-sizes.txt
@@ -0,0 +1,91 @@
+;;; TOOL: run-roundtrip
+;;; ARGS*: --stdout --enable-custom-page-sizes --enable-multi-memory --enable-memory64 --debug-names
+(module
+  (import "n" "mem2" (memory 23 (pagesize 1)))
+  (import "o" "mem3" (memory 24 25 (pagesize 1)))
+  (import "n" "mem2" (memory 23 (pagesize 65536)))
+  (import "o" "mem3" (memory 24 25 (pagesize 65536)))
+  (import "n" "mem2" (memory $g i64 23 (pagesize 1)))
+  (import "o" "mem3" (memory $h i64 24 25 (pagesize 1)))
+  (import "n" "mem2" (memory i64 23 (pagesize 65536)))
+  (import "o" "mem3" (memory i64 24 25 (pagesize 65536)))
+
+  (memory (import "m" "mem1") 107 (pagesize 1))
+  (memory (import "m" "mem1") 107 (pagesize 65536))
+  (memory $c (import "m" "mem1") i64 107 (pagesize 1))
+  (memory (import "m" "mem1") i64 107 (pagesize 65536))
+
+  (memory 57 (pagesize 1))
+  (memory 73 92 (pagesize 1))
+  (memory (pagesize 1) (data))
+  (memory (pagesize 1) (data "xyz"))
+  (memory 57 (pagesize 65536))
+  (memory 73 92 (pagesize 65536))
+  (memory (pagesize 65536) (data))
+  (memory (pagesize 65536) (data "xyz"))
+  (memory $a i64 57 (pagesize 1))
+  (memory $b i64 73 92 (pagesize 1))
+  (memory $d i64 (pagesize 1) (data))
+  (memory $e i64 (pagesize 1) (data "xyz"))
+  (memory $k i64 (data))
+  (memory $i i64 (pagesize 65536) (data))
+  (memory $j i64 (pagesize 65536) (data "xyz"))
+  (memory i64 57 (pagesize 65536))
+  (memory i64 73 92 (pagesize 65536))
+  (memory i64 (pagesize 65536) (data))
+  (memory i64 (pagesize 65536) (data "xyz"))
+
+  (memory 0xFFFF_FFFF (pagesize 1))
+  (memory i64 0xFFFF_FFFF_FFFF_FFFF (pagesize 1))
+  (memory 0x10000 (pagesize 0x10000))
+  (memory i64 0x1_0000_0000_0000 (pagesize 0x10000))
+)
+(;; STDOUT ;;;
+(module
+  (import "n" "mem2" (memory (;0;) 23 (pagesize 1)))
+  (import "o" "mem3" (memory (;1;) 24 25 (pagesize 1)))
+  (import "n" "mem2" (memory (;2;) 23))
+  (import "o" "mem3" (memory (;3;) 24 25))
+  (import "n" "mem2" (memory $g i64 23 (pagesize 1)))
+  (import "o" "mem3" (memory $h i64 24 25 (pagesize 1)))
+  (import "n" "mem2" (memory (;6;) i64 23))
+  (import "o" "mem3" (memory (;7;) i64 24 25))
+  (import "m" "mem1" (memory (;8;) 107 (pagesize 1)))
+  (import "m" "mem1" (memory (;9;) 107))
+  (import "m" "mem1" (memory $c i64 107 (pagesize 1)))
+  (import "m" "mem1" (memory (;11;) i64 107))
+  (memory (;12;) 57 (pagesize 1))
+  (memory (;13;) 73 92 (pagesize 1))
+  (memory (;14;) 0 0 (pagesize 1))
+  (memory (;15;) 3 3 (pagesize 1))
+  (memory (;16;) 57)
+  (memory (;17;) 73 92)
+  (memory (;18;) 0 0)
+  (memory (;19;) 1 1)
+  (memory $a i64 57 (pagesize 1))
+  (memory $b i64 73 92 (pagesize 1))
+  (memory $d i64 0 0 (pagesize 1))
+  (memory $e i64 3 3 (pagesize 1))
+  (memory $k i64 0 0)
+  (memory $i i64 0 0)
+  (memory $j i64 1 1)
+  (memory (;27;) i64 57)
+  (memory (;28;) i64 73 92)
+  (memory (;29;) i64 0 0)
+  (memory (;30;) i64 1 1)
+  (memory (;31;) 4294967295 (pagesize 1))
+  (memory (;32;) i64 18446744073709551615 (pagesize 1))
+  (memory (;33;) 65536)
+  (memory (;34;) i64 281474976710656)
+  (data (;0;) (memory 14) (i32.const 0) "")
+  (data (;1;) (memory 15) (i32.const 0) "xyz")
+  (data (;2;) (memory 18) (i32.const 0) "")
+  (data (;3;) (memory 19) (i32.const 0) "xyz")
+  (data (;4;) (memory $d) (i64.const 0) "")
+  (data (;5;) (memory $e) (i64.const 0) "xyz")
+  (data (;6;) (memory $k) (i64.const 0) "")
+  (data (;7;) (memory $i) (i64.const 0) "")
+  (data (;8;) (memory $j) (i64.const 0) "xyz")
+  (data (;9;) (memory 29) (i64.const 0) "")
+  (data (;10;) (memory 30) (i64.const 0) "xyz"))
+;;; STDOUT ;;)
diff --git a/test/run-roundtrip.py b/test/run-roundtrip.py
index 5260ec3e..69c4596f 100755
--- a/test/run-roundtrip.py
+++ b/test/run-roundtrip.py
@@ -114,6 +114,7 @@ def main(args):
     parser.add_argument('--enable-multi-memory', action='store_true')
     parser.add_argument('--enable-annotations', action='store_true')
     parser.add_argument('--enable-code-metadata', action='store_true')
+    parser.add_argument('--enable-custom-page-sizes', action='store_true')
     parser.add_argument('--inline-exports', action='store_true')
     parser.add_argument('--inline-imports', action='store_true')
     parser.add_argument('--reloc', action='store_true')
@@ -138,6 +139,7 @@ def main(args):
         '--enable-multi-memory': options.enable_multi_memory,
         '--enable-annotations': options.enable_annotations,
         '--enable-code-metadata': options.enable_code_metadata,
+        '--enable-custom-page-sizes': options.enable_custom_page_sizes,
         '--reloc': options.reloc,
         '--no-check': options.no_check,
     })
@@ -160,6 +162,7 @@ def main(args):
         '--enable-multi-memory': options.enable_multi_memory,
         '--enable-annotations': options.enable_annotations,
         '--enable-code-metadata': options.enable_code_metadata,
+        '--enable-custom-page-sizes': options.enable_custom_page_sizes,
         '--inline-exports': options.inline_exports,
         '--inline-imports': options.inline_imports,
         '--no-debug-names': not options.debug_names,
diff --git a/test/spec/custom-page-sizes/custom-page-sizes-invalid.txt b/test/spec/custom-page-sizes/custom-page-sizes-invalid.txt
new file mode 100644
index 00000000..3ae9fa74
--- /dev/null
+++ b/test/spec/custom-page-sizes/custom-page-sizes-invalid.txt
@@ -0,0 +1,63 @@
+;;; TOOL: run-interp-spec
+;;; ARGS*: --enable-custom-page-sizes --enable-multi-memory
+;;; STDIN_FILE: third_party/testsuite/proposals/custom-page-sizes/custom-page-sizes-invalid.wast
+(;; STDOUT ;;;
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:3: assert_malformed passed:
+  out/test/spec/custom-page-sizes/custom-page-sizes-invalid/custom-page-sizes-invalid.0.wat:1:21: error: malformed custom page size
+  (memory 0 (pagesize 3))
+                      ^
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:9: assert_invalid passed:
+  out/test/spec/custom-page-sizes/custom-page-sizes-invalid/custom-page-sizes-invalid.1.wasm:000000e: error: only page sizes of 1 B or 64 KiB are allowed
+  000000e: error: OnMemory callback failed
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:13: assert_invalid passed:
+  out/test/spec/custom-page-sizes/custom-page-sizes-invalid/custom-page-sizes-invalid.2.wasm:000000e: error: only page sizes of 1 B or 64 KiB are allowed
+  000000e: error: OnMemory callback failed
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:17: assert_invalid passed:
+  out/test/spec/custom-page-sizes/custom-page-sizes-invalid/custom-page-sizes-invalid.3.wasm:000000e: error: only page sizes of 1 B or 64 KiB are allowed
+  000000e: error: OnMemory callback failed
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:21: assert_invalid passed:
+  out/test/spec/custom-page-sizes/custom-page-sizes-invalid/custom-page-sizes-invalid.4.wasm:000000e: error: only page sizes of 1 B or 64 KiB are allowed
+  000000e: error: OnMemory callback failed
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:25: assert_invalid passed:
+  out/test/spec/custom-page-sizes/custom-page-sizes-invalid/custom-page-sizes-invalid.5.wasm:000000e: error: only page sizes of 1 B or 64 KiB are allowed
+  000000e: error: OnMemory callback failed
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:29: assert_invalid passed:
+  out/test/spec/custom-page-sizes/custom-page-sizes-invalid/custom-page-sizes-invalid.6.wasm:000000e: error: only page sizes of 1 B or 64 KiB are allowed
+  000000e: error: OnMemory callback failed
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:33: assert_invalid passed:
+  out/test/spec/custom-page-sizes/custom-page-sizes-invalid/custom-page-sizes-invalid.7.wasm:000000e: error: only page sizes of 1 B or 64 KiB are allowed
+  000000e: error: OnMemory callback failed
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:37: assert_invalid passed:
+  out/test/spec/custom-page-sizes/custom-page-sizes-invalid/custom-page-sizes-invalid.8.wasm:000000e: error: only page sizes of 1 B or 64 KiB are allowed
+  000000e: error: OnMemory callback failed
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:41: assert_invalid passed:
+  out/test/spec/custom-page-sizes/custom-page-sizes-invalid/custom-page-sizes-invalid.9.wasm:000000e: error: only page sizes of 1 B or 64 KiB are allowed
+  000000e: error: OnMemory callback failed
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:45: assert_invalid passed:
+  out/test/spec/custom-page-sizes/custom-page-sizes-invalid/custom-page-sizes-invalid.10.wasm:000000e: error: only page sizes of 1 B or 64 KiB are allowed
+  000000e: error: OnMemory callback failed
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:49: assert_invalid passed:
+  out/test/spec/custom-page-sizes/custom-page-sizes-invalid/custom-page-sizes-invalid.11.wasm:000000e: error: only page sizes of 1 B or 64 KiB are allowed
+  000000e: error: OnMemory callback failed
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:53: assert_invalid passed:
+  out/test/spec/custom-page-sizes/custom-page-sizes-invalid/custom-page-sizes-invalid.12.wasm:000000e: error: only page sizes of 1 B or 64 KiB are allowed
+  000000e: error: OnMemory callback failed
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:57: assert_invalid passed:
+  out/test/spec/custom-page-sizes/custom-page-sizes-invalid/custom-page-sizes-invalid.13.wasm:000000e: error: only page sizes of 1 B or 64 KiB are allowed
+  000000e: error: OnMemory callback failed
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:61: assert_invalid passed:
+  out/test/spec/custom-page-sizes/custom-page-sizes-invalid/custom-page-sizes-invalid.14.wasm:000000e: error: only page sizes of 1 B or 64 KiB are allowed
+  000000e: error: OnMemory callback failed
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:65: assert_invalid passed:
+  out/test/spec/custom-page-sizes/custom-page-sizes-invalid/custom-page-sizes-invalid.15.wasm:000000e: error: only page sizes of 1 B or 64 KiB are allowed
+  000000e: error: OnMemory callback failed
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:71: assert_invalid passed:
+  000000e: error: malformed memory page size
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:78: assert_malformed passed:
+  000000e: error: malformed memory page size
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:99: assert_unlinkable passed:
+  error: page_size mismatch in imported memory, expected 65536 but got 1.
+out/test/spec/custom-page-sizes/custom-page-sizes-invalid.wast:106: assert_unlinkable passed:
+  error: page_size mismatch in imported memory, expected 1 but got 65536.
+21/21 tests passed.
+;;; STDOUT ;;)
diff --git a/test/spec/custom-page-sizes/custom-page-sizes.txt b/test/spec/custom-page-sizes/custom-page-sizes.txt
new file mode 100644
index 00000000..7e11e710
--- /dev/null
+++ b/test/spec/custom-page-sizes/custom-page-sizes.txt
@@ -0,0 +1,9 @@
+;;; TOOL: run-interp-spec
+;;; ARGS*: --enable-custom-page-sizes --enable-multi-memory
+;;; STDIN_FILE: third_party/testsuite/proposals/custom-page-sizes/custom-page-sizes.wast
+(;; STDOUT ;;;
+out/test/spec/custom-page-sizes/custom-page-sizes.wast:27: assert_trap passed: out of bounds memory access: access at 0+1 >= max value 0
+out/test/spec/custom-page-sizes/custom-page-sizes.wast:34: assert_trap passed: out of bounds memory access: access at 65536+1 >= max value 65536
+out/test/spec/custom-page-sizes/custom-page-sizes.wast:41: assert_trap passed: out of bounds memory access: access at 131072+1 >= max value 131072
+34/34 tests passed.
+;;; STDOUT ;;)
diff --git a/test/spec/memory64/binary.txt b/test/spec/memory64/binary.txt
index 28441993..e34a5f79 100644
--- a/test/spec/memory64/binary.txt
+++ b/test/spec/memory64/binary.txt
@@ -137,9 +137,9 @@ out/test/spec/memory64/binary.wast:633: assert_malformed passed:
 out/test/spec/memory64/binary.wast:651: assert_malformed passed:
   000000b: error: invalid memory count 1, only 0 bytes left in section
 out/test/spec/memory64/binary.wast:661: assert_malformed passed:
-  000000c: error: malformed memory limits flag: 8
+  000000c: error: custom page sizes not allowed
 out/test/spec/memory64/binary.wast:669: assert_malformed passed:
-  000000c: error: malformed memory limits flag: 8
+  000000c: error: custom page sizes not allowed
 out/test/spec/memory64/binary.wast:678: assert_malformed passed:
   000000c: error: malformed memory limits flag: 129
 out/test/spec/memory64/binary.wast:687: assert_malformed passed: