[llvm] [LLVM][Clang][AArch64] Implement AArch64 build attributes (PR #118771)

[Oliver Stannard via llvm-commits]

================
@@ -294,6 +379,58 @@ AArch64ELFStreamer &AArch64TargetELFStreamer::getStreamer() {
   return static_cast<AArch64ELFStreamer &>(Streamer);
 }
 
+void AArch64TargetELFStreamer::emitSubsection(unsigned Vendor,
+                                              unsigned IsMandatory,
+                                              unsigned ParameterType) {
+  StringRef VendorAsStr = ARMBuildAttrs::vendorToStr(Vendor);
+
+  // If exists, return.
+  for (MCELFStreamer::AttributeSubSection &SubSection : AttributeSubSections) {
+    if (SubSection.Vendor == VendorAsStr) {
+      llvm_unreachable("AArch64 build attributes subsection already exists");
----------------
ostannard wrote:

Is it not valid to switch back to a previous subsection, for example from user-written assembly directives?

https://github.com/llvm/llvm-project/pull/118771