From cdb0a718561faceeef6bf52e851b5841aee00926 Mon Sep 17 00:00:00 2001
From: Ayke van Laethem <aykevanlaethem@gmail.com>
Date: Wed, 21 May 2025 12:33:44 +0200
Subject: [PATCH] wasm: fix C realloc and optimize it a bit

  - Do not use make([]byte, ...) to allocate, instead call the allocator
    directly with a nil (undefined) layout. This makes sure the precise
    GC will scan the contents of the allocation, since C could very well
    put pointers in there.
  - Simplify the map to use the pointer as the key and the size as the
    value, instead of storing the slices directly in the map.
---
 compiler/map.go                       |  3 +++
 src/runtime/arch_tinygowasm_malloc.go | 31 ++++++++++++++++-----------
 2 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/compiler/map.go b/compiler/map.go
index eb45e6b53d..6aaf8c76c6 100644
--- a/compiler/map.go
+++ b/compiler/map.go
@@ -250,6 +250,9 @@ func (b *builder) createMapIteratorNext(rangeVal ssa.Value, llvmRangeVal, it llv
 func hashmapIsBinaryKey(keyType types.Type) bool {
 	switch keyType := keyType.Underlying().(type) {
 	case *types.Basic:
+		// TODO: unsafe.Pointer is also a binary key, but to support that we
+		// need to fix an issue with interp first (see
+		// https://github.com/tinygo-org/tinygo/pull/4898).
 		return keyType.Info()&(types.IsBoolean|types.IsInteger) != 0
 	case *types.Pointer:
 		return true
diff --git a/src/runtime/arch_tinygowasm_malloc.go b/src/runtime/arch_tinygowasm_malloc.go
index 8726328025..471361bd77 100644
--- a/src/runtime/arch_tinygowasm_malloc.go
+++ b/src/runtime/arch_tinygowasm_malloc.go
@@ -8,16 +8,21 @@ import "unsafe"
 // code linked from other languages can allocate memory without colliding with
 // our GC allocations.
 
-var allocs = make(map[uintptr][]byte)
+// Map of allocations, where the key is the allocated pointer and the value is
+// the size of the allocation.
+// TODO: make this a map[unsafe.Pointer]uintptr, since that results in slightly
+// smaller binaries. But for that to work, unsafe.Pointer needs to be seen as a
+// binary key (which it is not at the moment).
+// See https://github.com/tinygo-org/tinygo/pull/4898 for details.
+var allocs = make(map[*byte]uintptr)
 
 //export malloc
 func libc_malloc(size uintptr) unsafe.Pointer {
 	if size == 0 {
 		return nil
 	}
-	buf := make([]byte, size)
-	ptr := unsafe.Pointer(&buf[0])
-	allocs[uintptr(ptr)] = buf
+	ptr := alloc(size, nil)
+	allocs[(*byte)(ptr)] = size
 	return ptr
 }
 
@@ -26,8 +31,8 @@ func libc_free(ptr unsafe.Pointer) {
 	if ptr == nil {
 		return
 	}
-	if _, ok := allocs[uintptr(ptr)]; ok {
-		delete(allocs, uintptr(ptr))
+	if _, ok := allocs[(*byte)(ptr)]; ok {
+		delete(allocs, (*byte)(ptr))
 	} else {
 		panic("free: invalid pointer")
 	}
@@ -48,18 +53,20 @@ func libc_realloc(oldPtr unsafe.Pointer, size uintptr) unsafe.Pointer {
 
 	// It's hard to optimize this to expand the current buffer with our GC, but
 	// it is theoretically possible. For now, just always allocate fresh.
-	buf := make([]byte, size)
+	// TODO: we could skip this if the new allocation is smaller than the old.
+	ptr := alloc(size, nil)
 
 	if oldPtr != nil {
-		if oldBuf, ok := allocs[uintptr(oldPtr)]; ok {
-			copy(buf, oldBuf)
-			delete(allocs, uintptr(oldPtr))
+		if oldSize, ok := allocs[(*byte)(oldPtr)]; ok {
+			oldBuf := unsafe.Slice((*byte)(oldPtr), oldSize)
+			newBuf := unsafe.Slice((*byte)(ptr), size)
+			copy(newBuf, oldBuf)
+			delete(allocs, (*byte)(oldPtr))
 		} else {
 			panic("realloc: invalid pointer")
 		}
 	}
 
-	ptr := unsafe.Pointer(&buf[0])
-	allocs[uintptr(ptr)] = buf
+	allocs[(*byte)(ptr)] = size
 	return ptr
 }