Fix #4
This fixes the long standing bug with strict aliasing that caused heavily JITed code to miscompile. It stemmed first from pointer reinterpretation which is simply undefined behavior. After fixing that with an `union` and `ffi.copy`, the issue manifested in a different way. Further debugging showed that it was likely that `ffi.copy` (and `ffi.C.memcpy`) would still alias pointers through coercion, more undefined behavior. Now, memory is handled with an `Any` type instead, so aliasing does not occur although unaligned reads and writes may be a problem in the future. I hope this doesn't break. It was very painful to debug.
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Rerumu
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415f61cb2a
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@ -298,10 +298,10 @@ end
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do
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local load = {}
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local store = {}
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local memory = {}
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local copy = ffi.copy
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local RE_INSTANCE = ffi.new [[union {
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ffi.cdef [[
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union Any {
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int8_t i8;
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int16_t i16;
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int32_t i32;
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@ -314,160 +314,12 @@ do
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float f32;
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double f64;
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}]]
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};
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function load.i32_i8(memory, addr)
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copy(RE_INSTANCE, memory.data + addr, 1)
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return RE_INSTANCE.i8
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end
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function load.i32_u8(memory, addr)
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copy(RE_INSTANCE, memory.data + addr, 1)
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return RE_INSTANCE.u8
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end
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function load.i32_i16(memory, addr)
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copy(RE_INSTANCE, memory.data + addr, 2)
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return RE_INSTANCE.i16
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end
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function load.i32_u16(memory, addr)
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copy(RE_INSTANCE, memory.data + addr, 2)
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return RE_INSTANCE.u16
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end
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function load.i32(memory, addr)
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copy(RE_INSTANCE, memory.data + addr, 4)
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return RE_INSTANCE.i32
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end
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function load.i64_i8(memory, addr)
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copy(RE_INSTANCE, memory.data + addr, 1)
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return i64(RE_INSTANCE.i8)
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end
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function load.i64_u8(memory, addr)
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copy(RE_INSTANCE, memory.data + addr, 1)
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return i64(RE_INSTANCE.u8)
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end
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function load.i64_i16(memory, addr)
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copy(RE_INSTANCE, memory.data + addr, 2)
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return i64(RE_INSTANCE.i16)
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end
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function load.i64_u16(memory, addr)
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copy(RE_INSTANCE, memory.data + addr, 2)
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return i64(RE_INSTANCE.u16)
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end
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function load.i64_i32(memory, addr)
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copy(RE_INSTANCE, memory.data + addr, 4)
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return i64(RE_INSTANCE.i32)
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end
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function load.i64_u32(memory, addr)
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copy(RE_INSTANCE, memory.data + addr, 4)
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return i64(RE_INSTANCE.u32)
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end
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function load.i64(memory, addr)
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copy(RE_INSTANCE, memory.data + addr, 8)
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return RE_INSTANCE.i64
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end
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function load.f32(memory, addr)
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copy(RE_INSTANCE, memory.data + addr, 4)
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return RE_INSTANCE.f32
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end
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function load.f64(memory, addr)
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copy(RE_INSTANCE, memory.data + addr, 8)
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return RE_INSTANCE.f64
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end
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function store.i32_n8(memory, addr, value)
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RE_INSTANCE.i32 = value
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copy(memory.data + addr, RE_INSTANCE, 1)
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end
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function store.i32_n16(memory, addr, value)
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RE_INSTANCE.i32 = value
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copy(memory.data + addr, RE_INSTANCE, 2)
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end
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function store.i32(memory, addr, value)
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RE_INSTANCE.i32 = value
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copy(memory.data + addr, RE_INSTANCE, 4)
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end
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function store.i64_n8(memory, addr, value)
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RE_INSTANCE.i64 = value
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copy(memory.data + addr, RE_INSTANCE, 1)
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end
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function store.i64_n16(memory, addr, value)
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RE_INSTANCE.i64 = value
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copy(memory.data + addr, RE_INSTANCE, 2)
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end
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function store.i64_n32(memory, addr, value)
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RE_INSTANCE.i64 = value
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copy(memory.data + addr, RE_INSTANCE, 4)
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end
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function store.i64(memory, addr, value)
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RE_INSTANCE.i64 = value
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copy(memory.data + addr, RE_INSTANCE, 8)
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end
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function store.f32(memory, addr, value)
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RE_INSTANCE.f32 = value
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copy(memory.data + addr, RE_INSTANCE, 4)
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end
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function store.f64(memory, addr, value)
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RE_INSTANCE.f64 = value
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copy(memory.data + addr, RE_INSTANCE, 8)
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end
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module.load = load
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module.store = store
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end
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do
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local memory = {}
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local WASM_PAGE_SIZE = 65536
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ffi.cdef [[
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struct Memory {
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uint32_t min;
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uint32_t max;
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uint8_t *data;
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union Any *data;
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};
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void *calloc(size_t num, size_t size);
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@ -475,6 +327,64 @@ do
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void free(void *ptr);
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]]
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local alias_t = ffi.typeof('uint8_t *')
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local any_t = ffi.typeof('union Any *')
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local cast = ffi.cast
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local function by_offset(pointer, offset)
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local aliased = cast(alias_t, pointer)
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return cast(any_t, aliased + offset)
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end
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function load.i32_i8(memory, addr) return by_offset(memory.data, addr).i8 end
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function load.i32_u8(memory, addr) return by_offset(memory.data, addr).u8 end
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function load.i32_i16(memory, addr) return by_offset(memory.data, addr).i16 end
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function load.i32_u16(memory, addr) return by_offset(memory.data, addr).u16 end
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function load.i32(memory, addr) return by_offset(memory.data, addr).i32 end
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function load.i64_i8(memory, addr) return i64(by_offset(memory.data, addr).i8) end
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function load.i64_u8(memory, addr) return i64(by_offset(memory.data, addr).u8) end
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function load.i64_i16(memory, addr) return i64(by_offset(memory.data, addr).i16) end
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function load.i64_u16(memory, addr) return i64(by_offset(memory.data, addr).u16) end
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function load.i64_i32(memory, addr) return i64(by_offset(memory.data, addr).i32) end
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function load.i64_u32(memory, addr) return i64(by_offset(memory.data, addr).u32) end
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function load.i64(memory, addr) return by_offset(memory.data, addr).i64 end
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function load.f32(memory, addr) return by_offset(memory.data, addr).f32 end
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function load.f64(memory, addr) return by_offset(memory.data, addr).f64 end
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function store.i32_n8(memory, addr, value) by_offset(memory.data, addr).i8 = value end
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function store.i32_n16(memory, addr, value) by_offset(memory.data, addr).i16 = value end
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function store.i32(memory, addr, value) by_offset(memory.data, addr).i32 = value end
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function store.i64_n8(memory, addr, value) by_offset(memory.data, addr).i8 = value end
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function store.i64_n16(memory, addr, value) by_offset(memory.data, addr).i16 = value end
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function store.i64_n32(memory, addr, value) by_offset(memory.data, addr).i32 = value end
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function store.i64(memory, addr, value) by_offset(memory.data, addr).i64 = value end
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function store.f32(memory, addr, value) by_offset(memory.data, addr).f32 = value end
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function store.f64(memory, addr, value) by_offset(memory.data, addr).f64 = value end
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local WASM_PAGE_SIZE = 65536
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local function finalizer(memory) ffi.C.free(memory.data) end
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local function grow_unchecked(memory, old, new)
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@ -482,7 +392,7 @@ do
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assert(memory.data ~= nil, 'failed to reallocate')
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ffi.fill(memory.data + old, new - old, 0)
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ffi.fill(by_offset(memory.data, old), new - old, 0)
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end
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function memory.new(min, max)
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@ -495,7 +405,7 @@ do
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return ffi.gc(memory, finalizer)
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end
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function memory.init(memory, offset, data) ffi.copy(memory.data + offset, data) end
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function memory.init(memory, addr, data) ffi.copy(by_offset(memory.data, addr), data) end
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function memory.grow(memory, num)
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local old = memory.min
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@ -511,6 +421,8 @@ do
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end
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end
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module.load = load
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module.store = store
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module.memory = memory
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end
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