[lld] [LLD][COFF] Add support for alternate entry point in CHPE metadata on ARM64X (PR #123346)

[Martin Storsjö via llvm-commits]

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@@ -1235,17 +1240,31 @@ void DynamicRelocsChunk::writeTo(uint8_t *buf) const {
   header->Symbol = IMAGE_DYNAMIC_RELOCATION_ARM64X;
   buf += sizeof(*header);
 
-  auto pageHeader = reinterpret_cast<coff_base_reloc_block_header *>(buf);
-  pageHeader->BlockSize = sizeof(*pageHeader);
+  coff_base_reloc_block_header *pageHeader = nullptr;
+  size_t relocSize = 0;
   for (const Arm64XDynamicRelocEntry &entry : arm64xRelocs) {
-    entry.writeTo(buf + pageHeader->BlockSize);
-    pageHeader->BlockSize += entry.getSize();
+    uint32_t page = entry.offset.get() & ~0xfff;
+    if (!pageHeader || page != pageHeader->PageRVA) {
+      relocSize = alignTo(relocSize, sizeof(uint32_t));
+      if (pageHeader)
+        pageHeader->BlockSize =
+            buf + relocSize - reinterpret_cast<uint8_t *>(pageHeader);
+      pageHeader =
+          reinterpret_cast<coff_base_reloc_block_header *>(buf + relocSize);
+      pageHeader->PageRVA = page;
+      relocSize += sizeof(*pageHeader);
+    }
+
+    entry.writeTo(buf + relocSize);
+    relocSize += entry.getSize();
   }
-  pageHeader->BlockSize = alignTo(pageHeader->BlockSize, sizeof(uint32_t));
+  relocSize = alignTo(relocSize, sizeof(uint32_t));
+  pageHeader->BlockSize =
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mstorsjo wrote:

Can we assume that we had a nonzero number of relocations here, so that `pageHeader` was initialized?

https://github.com/llvm/llvm-project/pull/123346