Use runtime config to limit memory instead of module editing (#82)

Author: anuraaga

internal/re2_wazero.go

@@ -7,7 +7,6 @@ import (
 	"context"
 	_ "embed"
 	"encoding/binary"
-	"encoding/hex"
 	"errors"
 	"os"
 	"runtime"
@@ -19,7 +18,6 @@ import (
 	"github.com/tetratelabs/wazero/api"
 	"github.com/tetratelabs/wazero/experimental"
 	"github.com/tetratelabs/wazero/imports/wasi_snapshot_preview1"
-
 	"github.com/wasilibs/go-re2/internal/memory"
 )
 
@@ -31,6 +29,11 @@ var (
 //go:embed wasm/libcre2.so
 var libre2 []byte
 
+// memoryWasm created by `wat2wasm --enable-threads internal/wasm/memory.wat -o internal/wasm/memory.wasm`
+//
+//go:embed wasm/memory.wasm
+var memoryWasm []byte
+
 var (
 	wasmRT       wazero.Runtime
 	wasmCompiled wazero.CompiledModule
@@ -149,11 +152,6 @@ func putChildModule(cm *childModule) {
 }
 
 func init() {
-	ctx := context.Background()
-	rt := wazero.NewRuntimeWithConfig(ctx, wazero.NewRuntimeConfig().WithCoreFeatures(api.CoreFeaturesV2|experimental.CoreFeaturesThreads))
-
-	wasi_snapshot_preview1.MustInstantiate(ctx, rt)
-
 	maxPages := uint32(65536)
 	if m := memory.TotalMemory(); m != 0 {
 		pages := uint32(m / 65536) // Divide by WASM page size
@@ -162,9 +160,14 @@ func init() {
 		}
 	}
 
-	mem := encodeMemory(maxPages)
+	ctx := context.Background()
+	rt := wazero.NewRuntimeWithConfig(ctx, wazero.NewRuntimeConfig().
+		WithCoreFeatures(api.CoreFeaturesV2|experimental.CoreFeaturesThreads).
+		WithMemoryLimitPages(maxPages))
+
+	wasi_snapshot_preview1.MustInstantiate(ctx, rt)
 
-	if _, err := rt.InstantiateWithConfig(ctx, mem, wazero.NewModuleConfig().WithName("env")); err != nil {
+	if _, err := rt.InstantiateWithConfig(ctx, memoryWasm, wazero.NewModuleConfig().WithName("env")); err != nil {
 		panic(err)
 	}
 
@@ -651,41 +654,3 @@ func (f *lazyFunction) callWithStack(ctx context.Context, callStack []uint64) (u
 	}
 	return callStack[0], nil
 }
-
-// Memory module is prefix, max pages, suffix, resulting a module looking like
-// (module (memory (export "memory") 3 <max> shared))
-const (
-	memoryPrefixHex = "0061736d010000000506010303"
-	memorySuffixHex = "070a01066d656d6f72790200"
-)
-
-func encodeMemory(maxPages uint32) []byte {
-	memoryPrefix, _ := hex.DecodeString(memoryPrefixHex)
-	memorySuffix, _ := hex.DecodeString(memorySuffixHex)
-	pages := encodeUint64(uint64(maxPages))
-	res := append([]byte(memoryPrefix), pages...)
-	return append(res, []byte(memorySuffix)...)
-}
-
-// From https://github.com/tetratelabs/wazero/blob/main/internal/leb128/leb128.go#L75
-
-func encodeUint64(value uint64) (buf []byte) {
-	// This is effectively a do/while loop where we take 7 bits of the value and encode them until it is zero.
-	for {
-		// Take 7 remaining low-order bits from the value into b.
-		b := uint8(value & 0x7f)
-		value = value >> 7
-
-		// If there are remaining bits, the value won't be zero: Set the high-
-		// order bit to tell the reader there are more bytes in this uint.
-		if value != 0 {
-			b |= 0x80
-		}
-
-		// Append b into the buffer
-		buf = append(buf, b)
-		if b&0x80 == 0 {
-			return buf
-		}
-	}
-}

internal/wasm/memory.wasm

@@ -0,0 +1 @@
+(module (memory (export "memory") 3 65536 shared))