[clang] [llvm] [aarch64][x86][win] Add compiler support for MSVC's /funcoverride flag (Windows kernel loader replaceable functions) (PR #125320)

[Eli Friedman via llvm-commits]

================
@@ -4661,3 +4661,109 @@ AsmPrinter::getCodeViewJumpTableInfo(int JTI, const MachineInstr *BranchInstr,
   return std::make_tuple(Base, 0, BranchLabel,
                          codeview::JumpTableEntrySize::Int32);
 }
+
+void AsmPrinter::emitCOFFReplaceableFunctionData(Module &M) {
+  const Triple &TT = TM.getTargetTriple();
+  assert(TT.isOSBinFormatCOFF());
+
+  bool IsTargetArm64EC = TT.isWindowsArm64EC();
+  SmallVector<char> Buf;
+  SmallVector<MCSymbol *> FuncOverrideDefaultSymbols;
+  bool SwitchedToDirectiveSection = false;
+  for (const Function &F : M.functions()) {
+    if (F.hasFnAttribute("loader-replaceable")) {
+      if (!SwitchedToDirectiveSection) {
+        OutStreamer->switchSection(
+            OutContext.getObjectFileInfo()->getDrectveSection());
+        SwitchedToDirectiveSection = true;
+      }
+
+      StringRef Name = F.getName();
+
+      // For hybrid-patchable targets, strip the prefix so that we can mark
+      // the real function as replaceable.
+      if (IsTargetArm64EC && Name.ends_with(HybridPatchableTargetSuffix)) {
+        Name = Name.substr(0, Name.size() - HybridPatchableTargetSuffix.size());
----------------
efriedma-quic wrote:

```suggestion
        Name = Name.drop_back(HybridPatchableTargetSuffix.size());
```

https://github.com/llvm/llvm-project/pull/125320