[clang] [llvm] [LFI] Add MCLFIRewriter infrastructure (PR #172906)

[Zachary Yedidia via llvm-commits]

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@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// LFI-specific MC implementation.
+///
+//===----------------------------------------------------------------------===//
+
+#include "llvm/MC/MCLFI.h"
+#include "llvm/BinaryFormat/ELF.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCLFIRewriter.h"
+#include "llvm/MC/MCSectionELF.h"
+#include "llvm/MC/MCStreamer.h"
+#include "llvm/MC/TargetRegistry.h"
+#include "llvm/Support/Alignment.h"
+#include "llvm/TargetParser/Triple.h"
+
+static const char NoteNamespace[] = "LFI";
+
+namespace llvm {
+
+cl::opt<bool> FlagEnableRewriting("lfi-enable-rewriter",
+                                  cl::desc("Enable rewriting for LFI."),
+                                  cl::init(true));
+
+void initializeLFIMCStreamer(MCStreamer &Streamer, MCContext &Ctx,
+                             const Triple &TheTriple) {
+  assert(TheTriple.isLFI());
+  const char *NoteName;
+  const char *NoteArch;
+  switch (TheTriple.getArch()) {
+  case Triple::aarch64:
+    NoteName = ".note.LFI.ABI.aarch64";
+    NoteArch = "aarch64";
+    break;
+  default:
+    reportFatalUsageError("Unsupported architecture for LFI");
+  }
+
+  std::string Error; // empty
+  const Target *TheTarget = TargetRegistry::lookupTarget(TheTriple, Error);
+
+  // Create the Target specific MCLFIRewriter.
+  assert(TheTarget != nullptr);
+  if (FlagEnableRewriting) {
+    TheTarget->createMCLFIRewriter(
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zyedidia wrote:

The ownership is manually handled by the backend-specific constructor. See https://github.com/llvm/llvm-project/pull/186896/changes#diff-25b1d6cc0406e6bd694b3fc463ee338186ef032edfd7c4db1c91326cd39af5cfR508.

However, we could make the API for `createMCLFIRewriter` return a raw pointer, consistent with the other `create*` functions and have this code call `Streamer.setLFIRewriter` directly (and create the `unique_ptr` at the call site), rather than doing that in the backend constructor. In that case the constructor will only need `MCContext` rather than `MCStreamer` as the first argument as well. I think this is cleaner so I can make the change in #186896.

https://github.com/llvm/llvm-project/pull/172906