[lld][WebAssembly] Add "--max-memory-growth"

With this option, clients (Emscripten) can implement non-growable
memories without knowing the amount of initial memory upfront.

Author: SingleAccretion

lld/docs/WebAssembly.rst

@@ -131,6 +131,10 @@ WebAssembly-specific options:
 
   Initial size of the linear memory. Default: the sum of stack, static data and heap sizes.
 
+.. option:: --max-memory-growth=<value>
+
+  Maximum size of memory that can be allocated dynamically. Default: unlimited.
+
 .. option:: --max-memory=<value>
 
   Maximum size of the linear memory. Default: unlimited.

lld/test/wasm/data-layout.s

@@ -103,6 +103,38 @@ local_struct_internal_ptr:
 # CHECK-MAX-NEXT:         Minimum:         0x2
 # CHECK-MAX-NEXT:         Maximum:         0x2
 
+# RUN: wasm-ld --no-entry --initial-memory=327680 --max-memory-growth=0 \
+# RUN:     -o %t_max.wasm %t.hello32.o
+# RUN: obj2yaml %t_max.wasm | FileCheck %s -check-prefix=CHECK-MAX-GROWTH-ZERO
+
+# CHECK-MAX-GROWTH-ZERO:        - Type:            MEMORY
+# CHECK-MAX-GROWTH-ZERO-NEXT:     Memories:
+# CHECK-MAX-GROWTH-ZERO:           - Flags:           [ HAS_MAX ]
+# CHECK-MAX-GROWTH-ZERO:             Minimum:         0x5
+# CHECK-MAX-GROWTH-ZERO:             Maximum:         0x5
+
+# RUN: wasm-ld --initial-memory=196608 --max-memory-growth=262144 \
+# RUN:     --no-entry -o %t_max.wasm %t.hello32.o
+# RUN: obj2yaml %t_max.wasm | FileCheck %s -check-prefix=CHECK-MAX-GROWTH-SOME
+
+# CHECK-MAX-GROWTH-SOME:        - Type:            MEMORY
+# CHECK-MAX-GROWTH-SOME-NEXT:     Memories:
+# CHECK-MAX-GROWTH-SOME:           - Flags:           [ HAS_MAX ]
+# CHECK-MAX-GROWTH-SOME:             Minimum:         0x3
+# CHECK-MAX-GROWTH-SOME:             Maximum:         0x7
+
+# RUN: not wasm-ld --max-memory-growth=131073 \
+# RUN:     --no-entry -o %t_max.wasm %t.hello32.o 2>&1 \
+# RUN: | FileCheck %s --check-prefix CHECK-MAX-GROWTH-ALIGN-ERROR
+
+# CHECK-MAX-GROWTH-ALIGN-ERROR: maximum memory growth must be 65536-byte aligned
+
+# RUN: not wasm-ld --initial-memory=131072 --max-memory=262144 --max-memory-growth=131072 \
+# RUN:     --no-entry -o %t_max.wasm %t.hello32.o 2>&1 \
+# RUN: | FileCheck %s --check-prefix CHECK-MAX-GROWTH-COMPAT-ERROR
+
+# CHECK-MAX-GROWTH-COMPAT-ERROR: --max-memory-growth and --max-memory are mutually exclusive
+
 # RUN: wasm-ld -no-gc-sections --allow-undefined --no-entry --shared-memory \
 # RUN:     --features=atomics,bulk-memory --initial-memory=131072 \
 # RUN:     --max-memory=131072 -o %t_max.wasm %t32.o %t.hello32.o

lld/test/wasm/large-memory.test

@@ -5,10 +5,16 @@ RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown %p/Inputs/start.s -o %
 RUN: wasm-ld %t.o -o %t1.wasm --max-memory=2147483648
 RUN: obj2yaml %t1.wasm | FileCheck %s --check-prefixes=CHECK,CHECK-2G
 
+RUN: wasm-ld %t.o -o %t1.wasm --initial-memory=131072 --max-memory-growth=2147352576
+RUN: obj2yaml %t1.wasm | FileCheck %s --check-prefixes=CHECK,CHECK-2G
+
 ; And also 4G of total memory
 RUN: wasm-ld %t.o -o %t2.wasm --max-memory=4294967296
 RUN: obj2yaml %t2.wasm | FileCheck %s --check-prefixes=CHECK,CHECK-4G
 
+RUN: wasm-ld %t.o -o %t2.wasm --initial-memory=131072 --max-memory-growth=4294836224
+RUN: obj2yaml %t2.wasm | FileCheck %s --check-prefixes=CHECK,CHECK-4G
+
 CHECK:      - Type:            MEMORY
 CHECK-NEXT:   Memories:
 CHECK-NEXT:     - Flags:           [ HAS_MAX ]
@@ -19,6 +25,8 @@ CHECK-4G-NEXT:    Maximum:         0x10000
 ; Test error for more than 4G of memory
 RUN: not wasm-ld %t.o -o %t3.wasm --initial-memory=4295032832 2>&1 | FileCheck %s --check-prefix INIT-ERROR
 RUN: not wasm-ld %t.o -o %t4.wasm --max-memory=4295032832 2>&1 | FileCheck %s --check-prefix MAX-ERROR
+RUN: not wasm-ld %t.o -o %t4.wasm --initial-memory=131072 --max-memory-growth=4294901760 2>&1 | FileCheck %s --check-prefix MAX-GROWTH-ERROR
 
 INIT-ERROR: initial memory too large, cannot be greater than 4294967296
 MAX-ERROR: maximum memory too large, cannot be greater than 4294967296
+MAX-GROWTH-ERROR: maximum memory growth too large, cannot be greater than 4294836224

lld/wasm/Config.h

@@ -77,6 +77,7 @@ struct Configuration {
   uint64_t globalBase;
   uint64_t initialHeap;
   uint64_t initialMemory;
+  uint64_t maxMemoryGrowth;
   uint64_t maxMemory;
   // The table offset at which to place function addresses.  We reserve zero
   // for the null function pointer.  This gets set to 1 for executables and 0

lld/wasm/Driver.cpp

@@ -541,6 +541,7 @@ static void readConfigs(opt::InputArgList &args) {
   config->globalBase = args::getInteger(args, OPT_global_base, 0);
   config->initialHeap = args::getInteger(args, OPT_initial_heap, 0);
   config->initialMemory = args::getInteger(args, OPT_initial_memory, 0);
+  config->maxMemoryGrowth = args::getInteger(args, OPT_max_memory_growth, -1);
   config->maxMemory = args::getInteger(args, OPT_max_memory, 0);
   config->zStackSize =
       args::getZOptionValue(args, OPT_z, "stack-size", WasmPageSize);

lld/wasm/Options.td

@@ -227,6 +227,9 @@ def initial_heap: JJ<"initial-heap=">,
 def initial_memory: JJ<"initial-memory=">,
   HelpText<"Initial size of the linear memory">;
 
+def max_memory_growth: JJ<"max-memory-growth=">,
+  HelpText<"Maximum size of dynamically allocatable linear memory">;
+
 def max_memory: JJ<"max-memory=">,
   HelpText<"Maximum size of the linear memory">;
 

lld/wasm/Writer.cpp

@@ -473,6 +473,25 @@ void Writer::layoutMemory() {
     WasmSym::heapEnd->setVA(memoryPtr);
   }
 
+  if (config->maxMemory != 0 && config->maxMemoryGrowth != -1) {
+    // Erroring out here is simpler than defining precedence rules.
+    error("--max-memory-growth and --max-memory are mutually exclusive");
+  }
+
+  uint64_t maxMemory = 0;
+  if (config->maxMemoryGrowth != -1) {
+    if (config->maxMemoryGrowth !=
+        alignTo(config->maxMemoryGrowth, WasmPageSize))
+      error("maximum memory growth must be " + Twine(WasmPageSize) +
+            "-byte aligned");
+    uint64_t maxMaxMemoryGrowth = maxMemorySetting - memoryPtr;
+    if (config->maxMemoryGrowth > maxMaxMemoryGrowth)
+      error("maximum memory growth too large, cannot be greater than " +
+            Twine(maxMaxMemoryGrowth));
+
+    maxMemory = memoryPtr + config->maxMemoryGrowth;
+  }
+
   if (config->maxMemory != 0) {
     if (config->maxMemory != alignTo(config->maxMemory, WasmPageSize))
       error("maximum memory must be " + Twine(WasmPageSize) + "-byte aligned");
@@ -481,20 +500,21 @@ void Writer::layoutMemory() {
     if (config->maxMemory > maxMemorySetting)
       error("maximum memory too large, cannot be greater than " +
             Twine(maxMemorySetting));
+
+    maxMemory = config->maxMemory;
   }
 
-  // Check max if explicitly supplied or required by shared memory
-  if (config->maxMemory != 0 || config->sharedMemory) {
-    uint64_t max = config->maxMemory;
-    if (max == 0) {
-      // If no maxMemory config was supplied but we are building with
-      // shared memory, we need to pick a sensible upper limit.
-      if (ctx.isPic)
-        max = maxMemorySetting;
-      else
-        max = memoryPtr;
-    }
-    out.memorySec->maxMemoryPages = max / WasmPageSize;
+  // If no maxMemory config was supplied but we are building with
+  // shared memory, we need to pick a sensible upper limit.
+  if (config->sharedMemory && maxMemory == 0) {
+    if (ctx.isPic)
+      maxMemory = maxMemorySetting;
+    else
+      maxMemory = memoryPtr;
+  }
+
+  if (maxMemory != 0) {
+    out.memorySec->maxMemoryPages = maxMemory / WasmPageSize;
     log("mem: max pages   = " + Twine(out.memorySec->maxMemoryPages));
   }
 }