[lld] [AArch64][GCS][LLD] Introduce -zgcs-report-dynamic Command Line Option (PR #127787)

[Jack Styles via llvm-commits]

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@@ -1418,6 +1425,24 @@ std::vector<uint32_t> SharedFile::parseVerneed(const ELFFile<ELFT> &obj,
   return verneeds;
 }
 
+// To determine if a shared file can support the AArch64 GCS extension, the
+// program headers for the object need to be read. This ensures when input
+// options are read, appropriate warning/error messages can be emitted depending
+// on the user's command line options.
+template <typename ELFT>
+uint64_t
+SharedFile::parseGnuAttributes(const typename ELFT::PhdrRange headers) {
+  if (numElfPhdrs == 0)
+    return 0;
+  uint64_t attributes = 0;
+  for (unsigned i = 0; i < numElfPhdrs; i++)
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Stylie777 wrote:

I have updated the implementation here. It still scans the program headers, and uses the SHT_NOTE Section Header to locate the information in the section. Making an `InputSection` is not possible here as it needs the file to be an Obj file. Taking the approach used by the Android Linker and finding the note header, followed by the section contents itself, similar to `readGnuProperty` allows for it to correctly locate the GNU GCS attribute. 

I did investigate both using `readGnuProperty` and refactoring a part of the function that finds the attributes, however there are elements here that rely on either having an InputSection or the file being an Obj file so I feel having its own implementation for a SharedFile is ok here. I will continue to look to see if the `readGnuProperty` function can be refactored to avoid the duplication happening here.

https://github.com/llvm/llvm-project/pull/127787