[clang] [llvm] [BPF] Fix linking issues in static map initializers (PR #91310)

[via cfe-commits]

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@@ -1950,8 +1950,22 @@ ConstantLValueEmitter::tryEmitBase(const APValue::LValueBase &base) {
     if (D->hasAttr<WeakRefAttr>())
       return CGM.GetWeakRefReference(D).getPointer();
 
-    if (auto FD = dyn_cast<FunctionDecl>(D))
-      return CGM.GetAddrOfFunction(FD);
+    if (auto FD = dyn_cast<FunctionDecl>(D)) {
+      auto *C = CGM.GetAddrOfFunction(FD);
+
+      // we don't normally emit debug info for extern fns referenced via
+      // variable initialisers; BPF needs it since it generates BTF from
+      // debug info and bpftool demands BTF for every symbol linked
+      if (CGM.getTarget().getTriple().isBPF() && FD->getStorageClass() == SC_Extern) {
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yonghong-song wrote:

Thanks @efriedma-quic if the clang believes the declaration might not be necessary due to optimizaiton, it is okay to remove it as in that case kernel/bpf does not need it either.

https://github.com/llvm/llvm-project/pull/91310