[llvm] [llvm-readobj][COFF] Dump .modmeta section (PR #201695)

[via llvm-commits]

================
@@ -0,0 +1,117 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Windows-specific.
+// Definitions and a parser for the C++ 20 ".modmeta" section.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_OBJECT_COFFMODULEMAP_H
+#define LLVM_OBJECT_COFFMODULEMAP_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/Endian.h"
+#include "llvm/Support/Error.h"
+
+namespace llvm::object {
+
+struct COFFCxxModuleMetadataHeader {
+  uint8_t Version;
+  uint8_t Reserved;
+  /// Number of bytes used to encode module IDs.
+  uint8_t ModuleIndexWidth;
+  /// Number of bytes used to encode symbol IDs.
+  uint8_t SymbolIndexWidth;
+  /// Size of this header and the module lists.
+  support::ulittle32_t ModuleDataSize;
+};
+
+struct COFFCxxModuleMetadata {
+  uint8_t Version;
+  uint8_t Reserved;
+  /// Number of bytes used to encode module IDs.
+  uint8_t ModuleIndexWidth;
+  /// Number of bytes used to encode symbol IDs.
+  uint8_t SymbolIndexWidth;
+
+  /// Data for modules.
+  ///
+  /// Starts with a list of module IDs that are header units.
+  /// This is followed by a list of modules, which is terminated by the maximum
+  /// module ID (e.g. 0xff for Width=1). Each module starts with the ID followed
+  /// by a list of modules it depends on, a list of non-exported symbols, and a
+  /// list of exported symbols.
+  StringRef ModuleData;
+
+  /// List of null-terminated module names.
+  ///
+  /// The names are present in the order of the modules in \p ModuleData. Note
+  /// that the module with ID 0 does not have a name.
+  StringRef NamesData;
+};
+
+struct LLVM_ABI COFFCxxModuleMetadataReader {
+  COFFCxxModuleMetadataReader(const COFFCxxModuleMetadata &Map);
+
+  StringRef ModuleData;
+  StringRef NamesData;
+
+  uint8_t ModuleIndexWidth;
+  uint8_t SymbolIndexWidth;
+
+  bool hasModuleData() const;
+
+  Expected<uint32_t> readModuleID();
+  Expected<StringRef> readModuleName();
+
+  /// Read a list of modules.
+  ///
+  /// \param Visitor A callback that accepts an `ArrayRef` of `uint8_t`,
+  /// `ulittle16_t`, or `ulittle32_t` depending on the index width.
+  template <typename T> Error readModuleList(T &&Visitor) {
+    return readList(std::forward<T>(Visitor), ModuleIndexWidth);
+  }
+
+  /// Read a list of symbols.
+  ///
+  /// \param Visitor A callback that accepts an `ArrayRef` of `uint8_t`,
+  /// `ulittle16_t`, or `ulittle32_t` depending on the index width.
+  template <typename T> Error readSymbolList(T &&Visitor) {
+    return readList(std::forward<T>(Visitor), SymbolIndexWidth);
+  }
+
+private:
+  template <typename T> Error readList(T &&Visitor, uint8_t Width) {
+    Expected<ArrayRef<uint8_t>> List = readListImpl(Width);
+    if (!List)
+      return List.takeError();
+
+    if (Width == 1)
+      Visitor(*List);
+    else if (Width == 2)
+      Visitor(ArrayRef<support::ulittle16_t>(
+          reinterpret_cast<const support::ulittle16_t *>(List->data()),
+          List->size() / sizeof(support::ulittle16_t)));
+    else
+      Visitor(ArrayRef<support::ulittle32_t>(
+          reinterpret_cast<const support::ulittle32_t *>(List->data()),
+          List->size() / sizeof(support::ulittle32_t)));
----------------
Nerixyz wrote:

Turned it into a switch.

https://github.com/llvm/llvm-project/pull/201695