Emit the CodeView `S_ARMSWITCHTABLE` debug symbol for jump tables

The CodeView `S_ARMSWITCHTABLE` debug symbol is used to describe the layout of a jump table, it contains the following information:

* The address of the branch instruction that uses the jump table.
* The address of the jump table.
* The "base" address that the values in the jump table are relative to.
* The type of each entry (absolute pointer, a relative integer, a relative integer that is shifted).

Together this information can be used by debuggers and binary analysis tools to understand what an jump table indirect branch is doing and where it might jump to.

Documentation for the symbol can be found in the Microsoft PDB library dumper: https://github.com/microsoft/microsoft-pdb/blob/0fe89a942f9a0f8e061213313e438884f4c9b876/cvdump/dumpsym7.cpp#L5518

This change adds support to LLVM to emit the `S_ARMSWITCHTABLE` debug symbol as well as to dump it out (for testing purposes).

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D149367

1 files changed, 21 insertions, 0 deletions

diff --git a/llvm/lib/ObjectYAML/CodeViewYAMLSymbols.cpp b/llvm/lib/ObjectYAML/CodeViewYAMLSymbols.cpp
index 8d2028abfe9b..64e1a58aa71a 100644
--- a/llvm/lib/ObjectYAML/CodeViewYAMLSymbols.cpp
+++ b/llvm/lib/ObjectYAML/CodeViewYAMLSymbols.cpp
@@ -61,6 +61,7 @@ LLVM_YAML_DECLARE_ENUM_TRAITS(CPUType)
 LLVM_YAML_DECLARE_ENUM_TRAITS(RegisterId)
 LLVM_YAML_DECLARE_ENUM_TRAITS(TrampolineType)
 LLVM_YAML_DECLARE_ENUM_TRAITS(ThunkOrdinal)
+LLVM_YAML_DECLARE_ENUM_TRAITS(JumpTableEntrySize)
 
 LLVM_YAML_STRONG_TYPEDEF(StringRef, TypeName)
 
@@ -207,6 +208,15 @@ void ScalarEnumerationTraits<FrameCookieKind>::enumeration(
   }
 }
 
+void ScalarEnumerationTraits<JumpTableEntrySize>::enumeration(
+    IO &io, JumpTableEntrySize &FC) {
+  auto ThunkNames = getJumpTableEntrySizeNames();
+  for (const auto &E : ThunkNames) {
+    io.enumCase(FC, E.Name.str().c_str(),
+                static_cast<JumpTableEntrySize>(E.Value));
+  }
+}
+
 namespace llvm {
 namespace yaml {
 template <> struct MappingTraits<LocalVariableAddrRange> {
@@ -586,6 +596,17 @@ template <> void SymbolRecordImpl<AnnotationSym>::map(IO &IO) {
   IO.mapRequired("Strings", Symbol.Strings);
 }
 
+template <> void SymbolRecordImpl<JumpTableSym>::map(IO &IO) {
+  IO.mapRequired("BaseOffset", Symbol.BaseOffset);
+  IO.mapRequired("BaseSegment", Symbol.BaseSegment);
+  IO.mapRequired("SwitchType", Symbol.SwitchType);
+  IO.mapRequired("BranchOffset", Symbol.BranchOffset);
+  IO.mapRequired("TableOffset", Symbol.TableOffset);
+  IO.mapRequired("BranchSegment", Symbol.BranchSegment);
+  IO.mapRequired("TableSegment", Symbol.TableSegment);
+  IO.mapRequired("EntriesCount", Symbol.EntriesCount);
+}
+
 } // end namespace detail
 } // end namespace CodeViewYAML
 } // end namespace llvm