--- /dev/null
+++ dyld/dyld-1330/mach_o_writer/FunctionStartsWriter.cpp
@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) 2021 Apple Inc. All rights reserved.
+ *
+ * @APPLE_LICENSE_HEADER_START@
+ *
+ * This file contains Original Code and/or Modifications of Original Code
+ * as defined in and that are subject to the Apple Public Source License
+ * Version 2.0 (the 'License'). You may not use this file except in
+ * compliance with the License. Please obtain a copy of the License at
+ * http://www.opensource.apple.com/apsl/ and read it before using this
+ * file.
+ *
+ * The Original Code and all software distributed under the License are
+ * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
+ * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
+ * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
+ * Please see the License for the specific language governing rights and
+ * limitations under the License.
+ *
+ * @APPLE_LICENSE_HEADER_END@
+ */
+
+#include <assert.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+
+// mach_o
+#include "Misc.h"
+
+// mach_o_writer
+#include "FunctionStartsWriter.h"
+
+
+namespace mach_o {
+
+FunctionStartsWriter::FunctionStartsWriter(uint64_t prefLoadAddr, std::span<const uint64_t> functionAddresses) : FunctionStarts(nullptr, 0)
+{
+    uint64_t lastAddr = prefLoadAddr;
+    for (uint64_t addr : functionAddresses) {
+        // firmwares can built with an out of VM addr order of segments
+        assert(addr >= lastAddr
+                || lastAddr == prefLoadAddr && "function addresses not sorted");
+        // <rdar://problem/10422823> filter out zero-length atoms, so LC_FUNCTION_STARTS address can't spill into next section
+        if ( addr == lastAddr)
+            continue;
+        // FIXME: for 32-bit arm need to check thumbness
+        uint64_t delta = addr - lastAddr;
+        append_uleb128(delta);
+        lastAddr = addr;
+    }
+    // terminate delta encoded list
+    _bytes.push_back(0);
+    // 8-byte align
+    while ( (_bytes.size() % 8) != 0 )
+        _bytes.push_back(0);
+
+    // set up pointers to data can be parsed
+    _funcStartsBegin = _bytes.data();
+    _funcStartsEnd   = _bytes.data()+_bytes.size();
+}
+
+void FunctionStartsWriter::append_uleb128(uint64_t value)
+{
+    uint8_t byte;
+    do {
+        byte = value & 0x7F;
+        value &= ~0x7F;
+        if ( value != 0 )
+            byte |= 0x80;
+        _bytes.push_back(byte);
+        value = value >> 7;
+    } while( byte >= 0x80 );
+}
+
+
+
+
+} // namespace mach_o