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Rouven Broszeit
0f69d016a0
When using the latest wasi-libc I experienced a panic on an attempt to call realloc. My first attempt to add it to arch_tinygowasm.go was obviously not good (PR #2194). So here is another suggestion.
82 lines
1.9 KiB
Go
82 lines
1.9 KiB
Go
// +build gc.leaking
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package runtime
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// This GC implementation is the simplest useful memory allocator possible: it
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// only allocates memory and never frees it. For some constrained systems, it
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// may be the only memory allocator possible.
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import (
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"unsafe"
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)
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// Ever-incrementing pointer: no memory is freed.
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var heapptr = heapStart
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func alloc(size uintptr, layout unsafe.Pointer) unsafe.Pointer {
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// TODO: this can be optimized by not casting between pointers and ints so
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// much. And by using platform-native data types (e.g. *uint8 for 8-bit
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// systems).
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size = align(size)
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addr := heapptr
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heapptr += size
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for heapptr >= heapEnd {
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// Try to increase the heap and check again.
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if growHeap() {
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continue
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}
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// Failed to make the heap bigger, so we must really be out of memory.
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runtimePanic("out of memory")
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}
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for i := uintptr(0); i < uintptr(size); i += 4 {
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ptr := (*uint32)(unsafe.Pointer(addr + i))
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*ptr = 0
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}
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return unsafe.Pointer(addr)
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}
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func realloc(ptr unsafe.Pointer, size uintptr) unsafe.Pointer {
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newAlloc := alloc(size, nil)
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if ptr == nil {
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return newAlloc
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}
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// according to POSIX everything beyond the previous pointer's
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// size will have indeterminate values so we can just copy garbage
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memcpy(newAlloc, ptr, size)
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return newAlloc
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}
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func free(ptr unsafe.Pointer) {
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// Memory is never freed.
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}
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func GC() {
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// No-op.
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}
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func KeepAlive(x interface{}) {
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// Unimplemented. Only required with SetFinalizer().
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}
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func SetFinalizer(obj interface{}, finalizer interface{}) {
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// Unimplemented.
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}
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func initHeap() {
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// preinit() may have moved heapStart; reset heapptr
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ptr := heapStart
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if GOARCH == "wasm" {
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// llvm11 and llvm12 do not correctly align the heap on wasm
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ptr = align(ptr)
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}
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heapptr = ptr
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}
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// setHeapEnd sets a new (larger) heapEnd pointer.
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func setHeapEnd(newHeapEnd uintptr) {
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// This "heap" is so simple that simply assigning a new value is good
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// enough.
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heapEnd = newHeapEnd
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}
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