Custom allocator.

Author: ncruces

internal/util/alloc_other.go

@@ -3,21 +3,12 @@
 package util
 
 import (
-	"context"
 	"math"
 
 	"github.com/tetratelabs/wazero/experimental"
 	"golang.org/x/sys/unix"
 )
 
-func withAllocator(ctx context.Context) context.Context {
-	if math.MaxInt != math.MaxInt64 {
-		return ctx
-	}
-	return experimental.WithMemoryAllocator(ctx,
-		experimental.MemoryAllocatorFunc(newAllocator))
-}
-
 func newAllocator(cap, max uint64) experimental.LinearMemory {
 	// Round up to the page size.
 	rnd := uint64(unix.Getpagesize() - 1)
@@ -52,7 +43,9 @@ type mmappedMemory struct {
 }
 
 func (m *mmappedMemory) Reallocate(size uint64) []byte {
-	if com := uint64(len(m.buf)); com < size {
+	com := uint64(len(m.buf))
+	res := uint64(cap(m.buf))
+	if com < size && size < res {
 		// Round up to the page size.
 		rnd := uint64(unix.Getpagesize() - 1)
 		new := (size + rnd) &^ rnd

internal/util/alloc_unix.go

@@ -3,7 +3,6 @@
 package util
 
 import (
-	"context"
 	"math"
 	"reflect"
 	"unsafe"
@@ -12,27 +11,19 @@ import (
 	"golang.org/x/sys/windows"
 )
 
-func withAllocator(ctx context.Context) context.Context {
-	if math.MaxInt != math.MaxInt64 {
-		return ctx
-	}
-	return experimental.WithMemoryAllocator(ctx,
-		experimental.MemoryAllocatorFunc(newAllocator))
-}
-
 func newAllocator(cap, max uint64) experimental.LinearMemory {
 	// Round up to the page size.
 	rnd := uint64(windows.Getpagesize() - 1)
 	max = (max + rnd) &^ rnd
 	cap = (cap + rnd) &^ rnd
 
 	if max > math.MaxInt {
-		// This ensures int(max) overflows to a negative value,
-		// and unix.Mmap returns EINVAL.
+		// This ensures uintptr(max) overflows to a large value,
+		// and windows.VirtualAlloc returns an error.
 		max = math.MaxUint64
 	}
 	// Reserve max bytes of address space, to ensure we won't need to move it.
-	// A protected, private, anonymous mapping should not commit memory.
+	// This does not commit memory.
 	r, err := windows.VirtualAlloc(0, uintptr(max), windows.MEM_RESERVE, windows.PAGE_READWRITE)
 	if err != nil {
 		panic(err)
@@ -61,7 +52,9 @@ type virtualMemory struct {
 }
 
 func (m *virtualMemory) Reallocate(size uint64) []byte {
-	if com := uint64(len(m.buf)); com < size {
+	com := uint64(len(m.buf))
+	res := uint64(cap(m.buf))
+	if com < size && size < res {
 		// Round up to the page size.
 		rnd := uint64(windows.Getpagesize() - 1)
 		new := (size + rnd) &^ rnd

internal/util/alloc_windows.go

@@ -1,4 +1,4 @@
-//go:build (darwin || linux) && (amd64 || arm64 || riscv64) && !(sqlite3_flock || sqlite3_noshm || sqlite3_nosys)
+//go:build (darwin || linux) && (amd64 || arm64 || riscv64) && !(sqlite3_noshm || sqlite3_nosys)
 
 package util
 
@@ -8,9 +8,15 @@ import (
 	"unsafe"
 
 	"github.com/tetratelabs/wazero/api"
+	"github.com/tetratelabs/wazero/experimental"
 	"golang.org/x/sys/unix"
 )
 
+func withAllocator(ctx context.Context) context.Context {
+	return experimental.WithMemoryAllocator(ctx,
+		experimental.MemoryAllocatorFunc(newAllocator))
+}
+
 type mmapState struct {
 	regions []*MappedRegion
 }

internal/util/mmap.go

@@ -1,5 +1,11 @@
-//go:build !(darwin || linux) || !(amd64 || arm64 || riscv64) || sqlite3_flock || sqlite3_noshm || sqlite3_nosys
+//go:build !(darwin || linux || windows) || !(amd64 || arm64 || riscv64) || sqlite3_noshm || sqlite3_nosys
 
 package util
 
+import "context"
+
 type mmapState struct{}
+
+func withAllocator(ctx context.Context) context.Context {
+	return ctx
+}

internal/util/mmap_other.go

@@ -0,0 +1,16 @@
+//go:build (amd64 || arm64) && !(sqlite3_noshm || sqlite3_nosys)
+
+package util
+
+import (
+	"context"
+
+	"github.com/tetratelabs/wazero/experimental"
+)
+
+type mmapState struct{}
+
+func withAllocator(ctx context.Context) context.Context {
+	return experimental.WithMemoryAllocator(ctx,
+		experimental.MemoryAllocatorFunc(newAllocator))
+}