--- /dev/null
+++ dyld/dyld-1340/mach_o_writer/SplitSegWriter.cpp
@@ -0,0 +1,132 @@
+/*
+ * Copyright (c) 2017 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 <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+// mach_o
+#include "Misc.h"
+
+// mach_o_writer
+#include "SplitSegWriter.h"
+
+#include <map>
+
+// FIXME: We should get this from cctools
+#define DYLD_CACHE_ADJ_V2_FORMAT 0x7F
+
+using mach_o::SplitSegInfo;
+
+namespace mach_o {
+
+static void append_uleb128(uint64_t value, std::vector<uint8_t>& out)
+{
+    uint8_t byte;
+    do {
+        byte = value & 0x7F;
+        value &= ~0x7F;
+        if ( value != 0 )
+            byte |= 0x80;
+        out.push_back(byte);
+        value = value >> 7;
+    } while ( byte >= 0x80 );
+}
+
+SplitSegInfoWriter::SplitSegInfoWriter(std::span<const SplitSegInfo::Entry> entries) : SplitSegInfo(nullptr, 0)
+{
+    // Whole         :== <count> FromToSection+
+    // FromToSection :== <from-sect-index> <to-sect-index> <count> ToOffset+
+    // ToOffset      :== <to-sect-offset-delta> <count> FromOffset+
+    // FromOffset    :== <kind> <count> <from-sect-offset-delta>
+
+    typedef uint32_t                                  SectionIndexes;
+    typedef std::map<uint8_t, std::vector<uint64_t> > FromOffsetMap;
+    typedef std::map<uint64_t, FromOffsetMap>         ToOffsetMap;
+    typedef std::map<SectionIndexes, ToOffsetMap>     WholeMap;
+
+    // sort into group by adjustment kind
+    //fprintf(stderr, "_splitSegV2Infos.size=%lu\n", entries.size());
+    WholeMap whole;
+    for ( const Entry& entry : entries ) {
+        SectionIndexes comboIndex  = (uint32_t)entry.fromSectionIndex << 16 | (uint32_t)entry.toSectionIndex;
+        ToOffsetMap&   toOffsets   = whole[comboIndex];
+        FromOffsetMap& fromOffsets = toOffsets[entry.toSectionOffset];
+        fromOffsets[entry.kind].push_back(entry.fromSectionOffset);
+    }
+
+    // Add marker that this is V2 data
+    this->_bytes.reserve(8192);
+    this->_bytes.push_back(DYLD_CACHE_ADJ_V2_FORMAT);
+
+    // stream out
+    // Whole :== <count> FromToSection+
+    append_uleb128(whole.size(), this->_bytes);
+    for (auto& fromToSection : whole) {
+        uint8_t fromSectionIndex = fromToSection.first >> 16;
+        uint8_t toSectionIndex   = fromToSection.first & 0xFFFF;
+        ToOffsetMap& toOffsets   = fromToSection.second;
+        // FromToSection :== <from-sect-index> <to-sect-index> <count> ToOffset+
+        append_uleb128(fromSectionIndex, this->_bytes);
+        append_uleb128(toSectionIndex, this->_bytes);
+        append_uleb128(toOffsets.size(), this->_bytes);
+        //fprintf(stderr, "from sect=%d, to sect=%d, count=%lu\n", fromSectionIndex, toSectionIndex, toOffsets.size());
+        uint64_t lastToOffset = 0;
+        for (auto& fromToOffsets : toOffsets) {
+            uint64_t       toSectionOffset   = fromToOffsets.first;
+            FromOffsetMap& fromOffsets       = fromToOffsets.second;
+            // ToOffset    :== <to-sect-offset-delta> <count> FromOffset+
+            uint64_t toSectionDelta = toSectionOffset - lastToOffset;
+            append_uleb128(toSectionDelta, this->_bytes);
+            append_uleb128(fromOffsets.size(), this->_bytes);
+            for (auto& kindAndOffsets : fromOffsets) {
+                uint8_t kind = kindAndOffsets.first;
+                std::vector<uint64_t>& fromSectOffsets = kindAndOffsets.second;
+                // FromOffset :== <kind> <count> <from-sect-offset-delta>
+                append_uleb128(kind, this->_bytes);
+                append_uleb128(fromSectOffsets.size(), this->_bytes);
+                std::sort(fromSectOffsets.begin(), fromSectOffsets.end());
+                uint64_t lastFromOffset = 0;
+                for (uint64_t offset : fromSectOffsets) {
+                    append_uleb128(offset - lastFromOffset, this->_bytes);
+                    lastFromOffset = offset;
+                }
+            }
+            lastToOffset = toSectionOffset;
+        }
+    }
+
+
+    // always add zero byte to mark end
+    this->_bytes.push_back(0);
+
+    // pad to be 8-btye aligned
+    while ( (this->_bytes.size() % 8) != 0 )
+        this->_bytes.push_back(0);
+
+    // set up buffer
+    this->_infoStart = &this->_bytes.front();
+    this->_infoEnd   = &this->_bytes.back();
+}
+
+} // namepace mach_o