interp: fix copy() from/to external buffers

This includes copying from a //go:embed slice for example. The slice
with data is not available at interp time.

See: https://github.com/tinygo-org/tinygo/issues/4895

interp/interpreter.go

@@ -364,9 +364,22 @@ func (r *runner) run(fn *function, params []value, parentMem *memoryView, indent
 						continue
 					}
 					nBytes := uint32(n * elemSize)
+					srcObj := mem.get(src.index())
 					dstObj := mem.getWritable(dst.index())
+					if srcObj.buffer == nil || dstObj.buffer == nil {
+						// If the buffer is nil, it means the slice is external.
+						// This can happen for example when copying data out of
+						// a //go:embed slice, which is not available at interp
+						// time.
+						// See: https://github.com/tinygo-org/tinygo/issues/4895
+						err := r.runAtRuntime(fn, inst, locals, &mem, indent)
+						if err != nil {
+							return nil, mem, err
+						}
+						continue
+					}
 					dstBuf := dstObj.buffer.asRawValue(r)
-					srcBuf := mem.get(src.index()).buffer.asRawValue(r)
+					srcBuf := srcObj.buffer.asRawValue(r)
 					copy(dstBuf.buf[dst.offset():dst.offset()+nBytes], srcBuf.buf[src.offset():])
 					dstObj.buffer = dstBuf
 					mem.put(dst.index(), dstObj)

interp/testdata/slice-copy.ll

@@ -11,6 +11,10 @@ target triple = "x86_64--linux"
 @main.sliceDstUntaint.buf = internal global [2 x i8] zeroinitializer
 @main.sliceSrcTaint.buf = internal global [2 x i8] c"cd"
 @main.sliceDstTaint.buf = internal global [2 x i8] zeroinitializer
+@main.sliceSrcExternal1.buf = external global [2 x i8]
+@main.sliceDstExternal1.buf = internal global [2 x i8] zeroinitializer
+@main.sliceSrcExternal2.buf = internal global [2 x i8] zeroinitializer
+@main.sliceDstExternal2.buf = external global [2 x i8]
 
 declare i64 @runtime.sliceCopy(ptr %dst, ptr %src, i64 %dstLen, i64 %srcLen, i64 %elemSize) unnamed_addr
 
@@ -58,6 +62,14 @@ entry:
   %sliceDstTaint.val = load i8, ptr getelementptr inbounds (i8, ptr @main.sliceDstTaint.buf, i32 0)
   call void @runtime.printuint8(i8 %sliceDstTaint.val)
 
+  ; print(sliceDstExternal1[0])
+  %sliceDstExternal1.val = load i8, ptr getelementptr inbounds (i8, ptr @main.sliceDstExternal1.buf, i32 0)
+  call void @runtime.printuint8(i8 %sliceDstExternal1.val)
+
+  ; print(sliceDstExternal2[0])
+  %sliceDstExternal2.val = load i8, ptr getelementptr inbounds (i8, ptr @main.sliceDstExternal2.buf, i32 0)
+  call void @runtime.printuint8(i8 %sliceDstExternal2.val)
+
   ret void
 }
 
@@ -102,5 +114,11 @@ entry:
   call void @use(ptr @main.sliceSrcTaint.buf)
   %copy.n4 = call i64 @runtime.sliceCopy(ptr @main.sliceDstTaint.buf, ptr @main.sliceSrcTaint.buf, i64 2, i64 2, i64 1)
 
+  ; Test that copying from or into external buffers works correctly.
+  ; These copy operations must be done at runtime.
+  ; https://github.com/tinygo-org/tinygo/issues/4895
+  %copy.n5 = call i64 @runtime.sliceCopy(ptr @main.sliceDstExternal1.buf, ptr @main.sliceSrcExternal1.buf, i64 2, i64 2, i64 1)
+  %copy.n6 = call i64 @runtime.sliceCopy(ptr @main.sliceDstExternal2.buf, ptr @main.sliceSrcExternal2.buf, i64 2, i64 2, i64 1)
+
   ret void
 }

interp/testdata/slice-copy.out.ll

@@ -3,6 +3,10 @@ target triple = "x86_64--linux"
 
 @main.sliceSrcTaint.buf = internal global [2 x i8] c"cd"
 @main.sliceDstTaint.buf = internal global [2 x i8] zeroinitializer
+@main.sliceSrcExternal1.buf = external global [2 x i8]
+@main.sliceDstExternal1.buf = internal global [2 x i8] zeroinitializer
+@main.sliceSrcExternal2.buf = internal global [2 x i8] zeroinitializer
+@main.sliceDstExternal2.buf = external global [2 x i8]
 
 declare i64 @runtime.sliceCopy(ptr, ptr, i64, i64, i64) unnamed_addr
 
@@ -16,6 +20,8 @@ define void @runtime.initAll() unnamed_addr {
 entry:
   call void @use(ptr @main.sliceSrcTaint.buf)
   %copy.n4 = call i64 @runtime.sliceCopy(ptr @main.sliceDstTaint.buf, ptr @main.sliceSrcTaint.buf, i64 2, i64 2, i64 1)
+  %copy.n5 = call i64 @runtime.sliceCopy(ptr @main.sliceDstExternal1.buf, ptr @main.sliceSrcExternal1.buf, i64 2, i64 2, i64 1)
+  %copy.n6 = call i64 @runtime.sliceCopy(ptr @main.sliceDstExternal2.buf, ptr @main.sliceSrcExternal2.buf, i64 2, i64 2, i64 1)
   ret void
 }
 
@@ -28,5 +34,9 @@ entry:
   call void @runtime.printuint8(i8 97)
   %sliceDstTaint.val = load i8, ptr @main.sliceDstTaint.buf, align 1
   call void @runtime.printuint8(i8 %sliceDstTaint.val)
+  %sliceDstExternal1.val = load i8, ptr @main.sliceDstExternal1.buf, align 1
+  call void @runtime.printuint8(i8 %sliceDstExternal1.val)
+  %sliceDstExternal2.val = load i8, ptr @main.sliceDstExternal2.buf, align 1
+  call void @runtime.printuint8(i8 %sliceDstExternal2.val)
   ret void
 }