runtime: unify GC interface

Make sure every to-be-implemented GC can use the same interface. As a
result, a 1MB chunk of RAM is allocated on Unix systems on init instead
of allocating on demand.

src/runtime/arch_amd64.go

@@ -6,3 +6,8 @@ const GOARCH = "amd64"
 
 // The bitness of the CPU (e.g. 8, 32, 64).
 const TargetBits = 64
+
+// Align on word boundary.
+func align(ptr uintptr) uintptr {
+	return (ptr + 7) &^ 7
+}

src/runtime/arch_avr.go

@@ -12,4 +12,12 @@ const GOARCH = "avr"
 const TargetBits = 8
 
 //go:extern _heap_start
-var heapStart unsafe.Pointer
+var heapStartSymbol unsafe.Pointer
+
+var heapStart = uintptr(unsafe.Pointer(&heapStartSymbol))
+
+// Align on a word boundary.
+func align(ptr uintptr) uintptr {
+	// No alignment necessary on the AVR.
+	return ptr
+}

src/runtime/arch_tinygoarm.go

@@ -12,4 +12,11 @@ const GOARCH = "arm"
 const TargetBits = 32
 
 //go:extern _heap_start
-var heapStart unsafe.Pointer
+var heapStartSymbol unsafe.Pointer
+
+var heapStart = uintptr(unsafe.Pointer(&heapStartSymbol))
+
+// Align on word boundary.
+func align(ptr uintptr) uintptr {
+	return (ptr + 3) &^ 3
+}

src/runtime/arch_wasm.go

@@ -12,4 +12,11 @@ const GOARCH = "wasm"
 const TargetBits = 32
 
 //go:extern __heap_base
-var heapStart unsafe.Pointer
+var heapStartSymbol unsafe.Pointer
+
+var heapStart = uintptr(unsafe.Pointer(&heapStartSymbol))
+
+// Align on word boundary.
+func align(ptr uintptr) uintptr {
+	return (ptr + 3) &^ 3
+}

src/runtime/gc.go

@@ -1,12 +1,11 @@
-// +build !linux
-
 package runtime
 
 import (
 	"unsafe"
 )
 
-var heapptr = uintptr(unsafe.Pointer(&heapStart))
+// Ever-incrementing pointer: no memory is freed.
+var heapptr = heapStart
 
 func alloc(size uintptr) unsafe.Pointer {
 	// TODO: this can be optimized by not casting between pointers and ints so

src/runtime/runtime_avr.go

@@ -120,9 +120,3 @@ func abort() {
 		sleepWDT(WDT_PERIOD_2S)
 	}
 }
-
-// Align on a word boundary.
-func align(ptr uintptr) uintptr {
-	// No alignment necessary on the AVR.
-	return ptr
-}

src/runtime/runtime_tinygoarm.go

@@ -46,11 +46,6 @@ func abort() {
 	}
 }
 
-// Align on word boundary.
-func align(ptr uintptr) uintptr {
-	return (ptr + 3) &^ 3
-}
-
 // Implement memset for compiler-rt.
 //go:export memset
 func memset(ptr unsafe.Pointer, c byte, size uintptr) {

src/runtime/runtime_unix.go

@@ -8,10 +8,14 @@ import (
 
 func _Cfunc_putchar(c int) int
 func _Cfunc_usleep(usec uint) int
-func _Cfunc_calloc(nmemb, size uintptr) unsafe.Pointer
+func _Cfunc_malloc(size uintptr) unsafe.Pointer
 func _Cfunc_abort()
 func _Cfunc_clock_gettime(clk_id uint, ts *timespec)
 
+const heapSize = 1 * 1024 * 1024 // 1MB to start
+
+var heapStart = uintptr(_Cfunc_malloc(heapSize))
+
 type timeUnit int64
 
 const tickMicros = 1
@@ -62,27 +66,3 @@ func abort() {
 	// panic() exits with exit code 2.
 	_Cfunc_abort()
 }
-
-func alloc(size uintptr) unsafe.Pointer {
-	buf := _Cfunc_calloc(1, size)
-	if buf == nil {
-		runtimePanic("cannot allocate memory")
-	}
-	return buf
-}
-
-func free(ptr unsafe.Pointer) {
-	//C.free(ptr) // TODO
-}
-
-func GC() {
-	// Unimplemented.
-}
-
-func KeepAlive(x interface{}) {
-	// Unimplemented. Only required with SetFinalizer().
-}
-
-func SetFinalizer(obj interface{}, finalizer interface{}) {
-	// Unimplemented.
-}

src/runtime/runtime_wasm.go

@@ -44,11 +44,6 @@ func ticks() timeUnit {
 	return timestamp
 }
 
-// Align on word boundary.
-func align(ptr uintptr) uintptr {
-	return (ptr + 3) &^ 3
-}
-
 // Abort executes the wasm 'unreachable' instruction.
 func abort() {
 	trap()