--- dyld/dyld-1340/mach_o/SplitSeg.cpp
+++ dyld/dyld-1122.1/mach_o/SplitSeg.cpp
@@ -28,6 +28,10 @@
 #include "SplitSeg.h"
 #include "Misc.h"
 
+#if BUILDING_MACHO_WRITER
+#include <map>
+#endif
+
 // FIXME: We should get this from cctools
 #define DYLD_CACHE_ADJ_V2_FORMAT 0x7F
 
@@ -41,11 +45,6 @@
 Error SplitSegInfo::valid() const
 {
     return Error::none();
-}
-
-bool SplitSegInfo::hasMarker() const
-{
-    return (_infoStart == _infoEnd);
 }
 
 bool SplitSegInfo::isV1() const
@@ -112,7 +111,7 @@
                         return Error("malformed uleb128");
                     fromSectionOffset += delta;
                     bool stop = false;
-                    callback(Entry { (uint8_t)kind, (uint8_t)fromSectionIndex, (uint8_t)toSectionIndex, fromSectionOffset, toSectionOffset }, stop);
+                    callback(Entry { (uint8_t)kind, fromSectionIndex, fromSectionOffset, toSectionIndex, toSectionOffset }, stop);
                     if ( stop )
                         return Error::none();
                 }
@@ -123,4 +122,97 @@
     return Error::none();
 }
 
+#if BUILDING_MACHO_WRITER
+
+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 );
+}
+
+SplitSegInfo::SplitSegInfo(std::span<const Entry> entries)
+{
+    // 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", this->_writer._splitSegV2Infos.size());
+    WholeMap whole;
+    for ( const Entry& entry : entries ) {
+        //fprintf(stderr, "from=%d, to=%d\n", entry.fromSectionIndex, entry.toSectionIndex);
+        SectionIndexes index = (uint32_t)entry.fromSectionIndex << 16 | (uint32_t)entry.toSectionIndex;
+        ToOffsetMap& toOffsets = whole[index];
+        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+
+            append_uleb128(toSectionOffset - lastToOffset, 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();
+}
+
+#endif // BUILDING_MACHO_WRITER
+
 } // namepace mach_o