--- /dev/null
+++ dyld/dyld-1330/mach_o_writer/FunctionVariantsWriter.cpp
@@ -0,0 +1,105 @@
+/*
+ * 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 "Defines.h"
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <assert.h>
+
+
+#include "FunctionVariantsWriter.h"
+
+namespace mach_o {
+
+
+//
+// MARK: --- FunctionVariantsRuntimeTableWriter methods ---
+//
+
+FunctionVariantsRuntimeTableWriter* FunctionVariantsRuntimeTableWriter::make(Kind kind, size_t variantsCount)
+{
+    size_t size = offsetof(FunctionVariantsRuntimeTable, entries[variantsCount]);
+    FunctionVariantsRuntimeTableWriter* p = (FunctionVariantsRuntimeTableWriter*)::calloc(size, 1);
+    p->kind  = kind;
+    p->count = (uint32_t)variantsCount;
+    return p;
+}
+
+Error FunctionVariantsRuntimeTableWriter::setEntry(size_t index, uint32_t impl, bool implIsTableIndex, std::span<const uint8_t> flagIndexes)
+{
+    if ( index >= this->count )
+        return Error("index=%lu too large (max=%d)", index, this->count);
+    if ( flagIndexes.size() > 4 )
+        return Error("flagIndexes too large %lu (max 4)", flagIndexes.size());
+    this->entries[index] = { impl, implIsTableIndex };
+    memcpy(this->entries[index].flagBitNums, flagIndexes.data(), flagIndexes.size());
+    return Error::none();
+}
+
+
+//
+// MARK: --- FunctionVariantsWriter methods ---
+//
+
+
+FunctionVariantsWriter::FunctionVariantsWriter(std::span<const FunctionVariantsRuntimeTable*> entries)
+{
+    // compute size of linkedit blob to hold all FunctionVariantsRuntimeTable
+    const size_t firstOffset = sizeof(OnDiskFormat) + entries.size()*sizeof(uint32_t);
+    size_t       size        = firstOffset;
+    for ( const FunctionVariantsRuntimeTable* fvrt : entries )
+        size += fvrt->size();
+    size = (size+7) & (-8);  // LINKEDIT content must be pointer size aligned
+
+    // allocate byte vector to hold whole blob
+    _builtBytes.resize(size);
+    _bytes = _builtBytes;
+
+    // fill in blob header and all entries
+    OnDiskFormat* p             = header();
+    uint32_t      currentOffset = (uint32_t)firstOffset;
+    for ( const FunctionVariantsRuntimeTable* fvrt : entries ) {
+        p->tableOffsets[p->tableCount] = currentOffset;
+        p->tableCount++;
+        size_t entrySize = fvrt->size();
+        assert(currentOffset+entrySize <= size);
+        memcpy(&_builtBytes[currentOffset], fvrt, entrySize);
+        currentOffset += entrySize;
+    }
+}
+
+
+//
+// MARK: --- FunctionVariantFixupsWriter methods ---
+//
+
+FunctionVariantFixupsWriter::FunctionVariantFixupsWriter(std::span<const InternalFixup> entries)
+{
+    _builtBytes.resize(entries.size() * sizeof(InternalFixup));
+    memcpy(_builtBytes.data(), entries.data(), entries.size() * sizeof(InternalFixup));
+    _fixups = std::span<const InternalFixup>((InternalFixup*)_builtBytes.data(), entries.size());
+}
+
+
+} // namespace mach_o