[llvm] [BOLT] Add GNUPropertyRewriter and warn on AArch64 BTI note (PR #161206)

[Paschalis Mpeis via llvm-commits]

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@@ -0,0 +1,147 @@
+//===- bolt/Rewrite/GNUPropertyRewriter.cpp -------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Read the .gnu.property.note section.
+//
+//===----------------------------------------------------------------------===//
+
+#include "bolt/Rewrite/MetadataRewriter.h"
+#include "bolt/Rewrite/MetadataRewriters.h"
+#include "llvm/Support/Errc.h"
+
+using namespace llvm;
+using namespace bolt;
+
+namespace {
+
+class GNUPropertyRewriter final : public MetadataRewriter {
+
+  Expected<uint32_t> decodeGNUPropertyNote(StringRef Desc);
+
+public:
+  GNUPropertyRewriter(StringRef Name, BinaryContext &BC)
+      : MetadataRewriter(Name, BC) {}
+
+  Error sectionInitializer() override;
+};
+
+Error GNUPropertyRewriter::sectionInitializer() {
+
+  ErrorOr<BinarySection &> Sec =
+      BC.getUniqueSectionByName(".note.gnu.property");
+  if (!Sec)
+    return Error::success();
+
+  // Accumulate feature bits
+  uint32_t FeaturesAcc = 0;
+
+  StringRef Buf = Sec->getContents();
+  DataExtractor DE(Buf, BC.AsmInfo->isLittleEndian(),
+                   BC.AsmInfo->getCodePointerSize());
+  DataExtractor::Cursor Cursor(0);
+  while (Cursor && !DE.eof(Cursor)) {
+    const uint32_t NameSz = DE.getU32(Cursor);
+    const uint32_t DescSz = DE.getU32(Cursor);
+    const uint32_t Type = DE.getU32(Cursor);
+
+    StringRef Name =
+        NameSz ? Buf.slice(Cursor.tell(), Cursor.tell() + NameSz) : "<empty>";
+    Cursor.seek(alignTo(Cursor.tell() + NameSz, 4));
+
+    const uint64_t DescOffset = Cursor.tell();
+    StringRef Desc =
+        DescSz ? Buf.slice(DescOffset, DescOffset + DescSz) : "<empty>";
+    Cursor.seek(alignTo(DescOffset + DescSz, 4));
+    if (!Cursor)
+      return createStringError(
+          errc::executable_format_error,
+          "out of bounds while reading .gnu.property.note section: %s",
+          toString(Cursor.takeError()).c_str());
+
+    if (Type == ELF::NT_GNU_PROPERTY_TYPE_0 && Name.starts_with("GNU") &&
+        DescSz) {
+      auto Features = decodeGNUPropertyNote(Desc);
+      if (!Features)
+        return Features.takeError();
+      FeaturesAcc |= *Features;
+    }
+  }
+
+  if (BC.isAArch64()) {
+    BC.setUsesBTI(FeaturesAcc & llvm::ELF::GNU_PROPERTY_AARCH64_FEATURE_1_BTI);
+    if (BC.usesBTI())
+      BC.outs() << "BOLT-WARNING: binary is using BTI. Optimized binary may be "
+                   "corrupted\n";
+  }
+
+  return Error::success();
+}
+
+/// Desc contains an array of property descriptors. Each member has the
----------------
paschalis-mpeis wrote:

nit
```suggestion
/// \p Desc contains an array of property descriptors. Each member has the
```

https://github.com/llvm/llvm-project/pull/161206