DebugInfo: support for DW_FORM_implicit_const

Support for DW_FORM_implicit_const DWARFv5 feature.
When this form is used attribute value goes to .debug_abbrev section (as SLEB).
As this form would break any debug tool which doesn't support DWARFv5
it is guarded by dwarf version check. Attempt to use this form with
dwarf version <= 4 is considered a fatal error.

Differential Revision: https://reviews.llvm.org/D28456

llvm-svn: 291599

1 files changed, 28 insertions, 7 deletions

diff --git a/llvm/lib/DebugInfo/DWARF/DWARFAbbreviationDeclaration.cpp b/llvm/lib/DebugInfo/DWARF/DWARFAbbreviationDeclaration.cpp
index 6126470aa09..08bc74a81e9 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFAbbreviationDeclaration.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFAbbreviationDeclaration.cpp
@@ -56,13 +56,20 @@ DWARFAbbreviationDeclaration::extract(DataExtractor Data,
     auto A = static_cast<Attribute>(Data.getULEB128(OffsetPtr));
     auto F = static_cast<Form>(Data.getULEB128(OffsetPtr));
     if (A && F) {
-      auto FixedFormByteSize = DWARFFormValue::getFixedByteSize(F);
-      AttributeSpecs.push_back(AttributeSpec(A, F, FixedFormByteSize));
+      Optional<int64_t> V;
+      bool IsImplicitConst = (F == DW_FORM_implicit_const);
+      if (IsImplicitConst)
+        V = Data.getSLEB128(OffsetPtr);
+      else if (auto Size = DWARFFormValue::getFixedByteSize(F))
+        V = *Size;
+      AttributeSpecs.push_back(AttributeSpec(A, F, V));
+      if (IsImplicitConst)
+        continue;
       // If this abbrevation still has a fixed byte size, then update the
       // FixedAttributeSize as needed.
       if (FixedAttributeSize) {
-        if (FixedFormByteSize)
-          FixedAttributeSize->NumBytes += *FixedFormByteSize;
+        if (V)
+          FixedAttributeSize->NumBytes += *V;
         else {
           switch (F) {
           case DW_FORM_addr:
@@ -129,6 +136,8 @@ void DWARFAbbreviationDeclaration::dump(raw_ostream &OS) const {
       OS << formString;
     else
       OS << format("DW_FORM_Unknown_%x", Spec.Form);
+    if (Spec.isImplicitConst())
+      OS << '\t' << *Spec.ByteSizeOrValue;
     OS << '\n';
   }
   OS << '\n';
@@ -160,11 +169,15 @@ Optional<DWARFFormValue> DWARFAbbreviationDeclaration::getAttributeValue(
     if (*MatchAttrIndex == AttrIndex) {
       // We have arrived at the attribute to extract, extract if from Offset.
       DWARFFormValue FormValue(Spec.Form);
+      if (Spec.isImplicitConst()) {
+        FormValue.setSValue(*Spec.ByteSizeOrValue);
+        return FormValue;
+      }
       if (FormValue.extractValue(DebugInfoData, &Offset, &U))
         return FormValue;
     }
     // March Offset along until we get to the attribute we want.
-    if (Optional<uint8_t> FixedSize = Spec.getByteSize(U))
+    if (auto FixedSize = Spec.getByteSize(U))
       Offset += *FixedSize;
     else
       DWARFFormValue::skipValue(Spec.Form, DebugInfoData, &Offset, &U);
@@ -185,9 +198,17 @@ size_t DWARFAbbreviationDeclaration::FixedSizeInfo::getByteSize(
   return ByteSize;
 }
 
-Optional<uint8_t> DWARFAbbreviationDeclaration::AttributeSpec::getByteSize(
+Optional<int64_t> DWARFAbbreviationDeclaration::AttributeSpec::getByteSize(
     const DWARFUnit &U) const {
-  return ByteSize ? ByteSize : DWARFFormValue::getFixedByteSize(Form, &U);
+  if (isImplicitConst())
+    return 0;
+  if (ByteSizeOrValue)
+    return ByteSizeOrValue;
+  Optional<int64_t> S;
+  auto FixedByteSize = DWARFFormValue::getFixedByteSize(Form, &U);
+  if (FixedByteSize)
+    S = *FixedByteSize;
+  return S;
 }
 
 Optional<size_t> DWARFAbbreviationDeclaration::getFixedAttributesByteSize(