Merge pull request #431 from WebAssembly/rm-max-heap

Change linear memory max to be a hint

AstSemantics.md

@@ -86,7 +86,7 @@ be an untyped array of bytes, and it is unspecified how embedders map this array
 into their process' own [virtual memory][]. The linear memory is sandboxed; it
 does not alias the execution engine's internal data structures, the execution
 stack, local variables, or other process memory. The initial state of linear
-memory is specified by the [module](Modules.md#initial-state-of-linear-memory).
+memory is specified by the [module](Modules.md#linear-memory-section).
 
   [virtual memory]: https://en.wikipedia.org/wiki/Virtual_memory
 

BinaryEncoding.md

@@ -103,8 +103,9 @@ Yes:
    - A sequence of byte ranges within the binary and corresponding addresses in the linear memory
 
 
-All strings are encoded as null-terminated UTF8.
-Data segments represent initialized data that is loaded directly from the binary into the linear memory when the program starts (see [modules](Modules.md#initial-state-of-linear-memory)).
+All strings are encoded as null-terminated UTF8. Data segments represent
+initialized data that is loaded directly from the binary into the linear memory
+when the program starts (see [modules](Modules.md#linear-memory-section)).
 
 ## Serialized AST
 

Modules.md

@@ -8,7 +8,7 @@ is determined by the module it was loaded from.
 
 A module contains:
 * a set of [imports and exports](Modules.md#imports-and-exports);
-* a section defining the [initial state of linear memory](Modules.md#initial-state-of-linear-memory);
+* a section defining [linear memory](Modules.md#linear-memory-section);
 * a section containing [code](Modules.md#code-section);
 * after the MVP, sections containing [debugging/symbol information](Tooling.md) or
   a reference to separate files containing them; and
@@ -122,12 +122,23 @@ shared `malloc` and coordinated global address ranges). Instead, the
 [dynamic linking future feature](DynamicLinking.md) is intended
 to allow *explicitly* injecting multiple modules into the same instance.
 
-## Initial state of linear memory
+## Linear memory section
 
-A module will contain a section declaring the linear memory size (initial and
-maximum size allowed by [`grow_memory`](AstSemantics.md#resizing) and the
-initial contents of memory, analogous to `.data`, `.rodata`, `.bss` sections in
-native executables (see [binary encoding](BinaryEncoding.md#global-structure)).
+A module may contain an optional section declaring the use of linear memory
+by the module. If the section is absent, the linear memory operators
+`load`, `store`, `memory_size`, and `grow_memory` may not be used in the module.
+
+The linear memory section declares the initial [memory size](AstSemantics.md#linear-memory)
+(which may be subsequently increased by [`grow_memory`](AstSemantics.md#resizing)).
+
+The initial contents of linear memory are zero by default. However, the memory
+section contains a possibly-empty array of *segments* (analogous to `.data`)
+which can specify the initial contents of fixed `(offset, length)` ranges of
+memory.
+
+The linear memory section may also contain an optional hint declaring the expected
+maximum heap usage. This hint is not semantically visible but can help a
+WebAssembly engine to optimize `grow_memory`.
 
 ## Code section
 

Rationale.md

@@ -112,6 +112,11 @@ to communicate their own implementation details in a useful manner to the
 developer.
 
 
+## Linear memory disabled if no linear memory section
+
+See [#107](https://github.com/WebAssembly/spec/pull/107).
+
+
 ## Control Flow
 
 See [#299](https://github.com/WebAssembly/design/pull/299).