[llvm] [BPF] Support wrapping BPF map structs into nested, single field structs (PR #144097)

[Michal Rostecki via llvm-commits]

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@@ -976,11 +976,21 @@ void BTFDebug::visitMapDefType(const DIType *Ty, uint32_t &TypeId) {
   if (Tag != dwarf::DW_TAG_structure_type || CTy->isForwardDecl())
     return;
 
-  // Visit all struct members to ensure pointee type is visited
+  // Visit all struct members to ensure their types are visited.
   const DINodeArray Elements = CTy->getElements();
+  // In Aya/Rust, BPF maps are wrapped into nested types. Such wrapper types
+  // always have only one element. When encountering them, we need to visit its
+  // (only) element with an assumption that it might contain either an another
+  // wrapper, or an actual map struct.
+  const bool IsAWrapperType = Elements.size() == 1;
   for (const auto *Element : Elements) {
     const auto *MemberType = cast<DIDerivedType>(Element);
-    visitTypeEntry(MemberType->getBaseType());
+    if (IsAWrapperType) {
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vadorovsky wrote:

> but also I wonder if there's a more sensible way to do this.

Good point. Assuming that BPF map definitions should have only pointers and arrays, maybe we could assume that any `DICompositeType` element is a wrapper?

> What if we decide to have more than one element in the wrapper struct in the future?

Hard to imagine that happening, but the idea of recursively looking into `DICompositeType` elements should solve it.

https://github.com/llvm/llvm-project/pull/144097