[DWARF][RISCV] Add support for RISC-V relocations needed for debug info

When code relaxation is enabled many RISC-V fixups are not resolved but
instead relocations are emitted. This happens even for DWARF debug
sections. Therefore, to properly support the parsing of DWARF debug info
we need to be able to resolve RISC-V relocations. This patch adds:

* Support for RISC-V relocations in RelocationResolver
* DWARF support for two relocations per object file offset
* DWARF changes to support relocations in more DIE fields

The two relocations per offset change is needed because some RISC-V
relocations (used for label differences) come in pairs.

Relocations can also be emitted for DWARF fields where relocations were
not yet evaluated. Adding relocation support for some of these fields is
essencial. On the other hand, LLVM currently emits RISC-V relocations
for fixups that could be safely evaluated, since they can never be
affected by code relaxations. This patch also adds relocation support
for the fields affected by those extraneous relocations (the DWARF unit
entry Length, and the DWARF debug line entry TotalLength and
PrologueLength), for testing purposes.

Differential Revision: https://reviews.llvm.org/D62062
Patch by Luís Marques.

llvm-svn: 366402

6 files changed, 31 insertions, 11 deletions

diff --git a/llvm/lib/DebugInfo/DWARF/DWARFContext.cpp b/llvm/lib/DebugInfo/DWARF/DWARFContext.cpp
index 321e157665a..5ede9bf5961 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFContext.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFContext.cpp
@@ -1651,9 +1651,25 @@ public:
         //
         // TODO Don't store Resolver in every RelocAddrEntry.
         if (Supports && Supports(Reloc.getType())) {
-          Map->try_emplace(Reloc.getOffset(),
-                           RelocAddrEntry{SymInfoOrErr->SectionIndex, Reloc,
-                                          Resolver, SymInfoOrErr->Address});
+          auto I = Map->try_emplace(
+              Reloc.getOffset(),
+              RelocAddrEntry{SymInfoOrErr->SectionIndex, Reloc,
+                             SymInfoOrErr->Address,
+                             Optional<object::RelocationRef>(), 0, Resolver});
+          // If we didn't successfully insert that's because we already had a
+          // relocation for that offset. Store it as a second relocation in the
+          // same RelocAddrEntry instead.
+          if (!I.second) {
+            RelocAddrEntry &entry = I.first->getSecond();
+            if (entry.Reloc2) {
+              ErrorPolicy EP = HandleError(createError(
+                  "At most two relocations per offset are supported"));
+              if (EP == ErrorPolicy::Halt)
+                return;
+            }
+            entry.Reloc2 = Reloc;
+            entry.SymbolValue2 = SymInfoOrErr->Address;
+          }
         } else {
           SmallString<32> Type;
           Reloc.getTypeName(Type);
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFDataExtractor.cpp b/llvm/lib/DebugInfo/DWARF/DWARFDataExtractor.cpp
index 6f2f992f53e..b9adf8cb1d9 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFDataExtractor.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFDataExtractor.cpp
@@ -24,7 +24,10 @@ uint64_t DWARFDataExtractor::getRelocatedValue(uint32_t Size, uint32_t *Off,
     return A;
   if (SecNdx)
     *SecNdx = E->SectionIndex;
-  return E->Resolver(E->Reloc, E->SymbolValue, A);
+  uint64_t R = E->Resolver(E->Reloc, E->SymbolValue, A);
+  if (E->Reloc2)
+    R = E->Resolver(*E->Reloc2, E->SymbolValue2, R);
+  return R;
 }
 
 Optional<uint64_t>
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp b/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp
index 3ee5652a0eb..a1cb1e8582e 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFDebugLine.cpp
@@ -300,7 +300,7 @@ Error DWARFDebugLine::Prologue::parse(const DWARFDataExtractor &DebugLineData,
   const uint64_t PrologueOffset = *OffsetPtr;
 
   clear();
-  TotalLength = DebugLineData.getU32(OffsetPtr);
+  TotalLength = DebugLineData.getRelocatedValue(4, OffsetPtr);
   if (TotalLength == UINT32_MAX) {
     FormParams.Format = dwarf::DWARF64;
     TotalLength = DebugLineData.getU64(OffsetPtr);
@@ -325,7 +325,8 @@ Error DWARFDebugLine::Prologue::parse(const DWARFDataExtractor &DebugLineData,
     SegSelectorSize = DebugLineData.getU8(OffsetPtr);
   }
 
-  PrologueLength = DebugLineData.getUnsigned(OffsetPtr, sizeofPrologueLength());
+  PrologueLength =
+      DebugLineData.getRelocatedValue(sizeofPrologueLength(), OffsetPtr);
   const uint64_t EndPrologueOffset = PrologueLength + *OffsetPtr;
   MinInstLength = DebugLineData.getU8(OffsetPtr);
   if (getVersion() >= 4)
@@ -754,7 +755,7 @@ Error DWARFDebugLine::LineTable::parse(
         // requires the use of DW_LNS_advance_pc. Such assemblers, however,
         // can use DW_LNS_fixed_advance_pc instead, sacrificing compression.
         {
-          uint16_t PCOffset = DebugLineData.getU16(OffsetPtr);
+          uint16_t PCOffset = DebugLineData.getRelocatedValue(2, OffsetPtr);
           State.Row.Address.Address += PCOffset;
           if (OS)
             *OS
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFFormValue.cpp b/llvm/lib/DebugInfo/DWARF/DWARFFormValue.cpp
index b3e4c911b5a..290d35511cd 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFFormValue.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFFormValue.cpp
@@ -299,7 +299,7 @@ bool DWARFFormValue::extractValue(const DWARFDataExtractor &Data,
     case DW_FORM_data8:
     case DW_FORM_ref8:
     case DW_FORM_ref_sup8:
-      Value.uval = Data.getU64(OffsetPtr);
+      Value.uval = Data.getRelocatedValue(8, OffsetPtr);
       break;
     case DW_FORM_data16:
       // Treat this like a 16-byte block.
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFListTable.cpp b/llvm/lib/DebugInfo/DWARF/DWARFListTable.cpp
index 32bb6d329ae..e38e706227d 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFListTable.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFListTable.cpp
@@ -25,7 +25,7 @@ Error DWARFListTableHeader::extract(DWARFDataExtractor Data,
                        "%s table length at offset 0x%" PRIx32,
                        SectionName.data(), *OffsetPtr);
   // TODO: Add support for DWARF64.
-  HeaderData.Length = Data.getU32(OffsetPtr);
+  HeaderData.Length = Data.getRelocatedValue(4, OffsetPtr);
   if (HeaderData.Length == 0xffffffffu)
     return createStringError(errc::not_supported,
                        "DWARF64 is not supported in %s at offset 0x%" PRIx32,
@@ -73,7 +73,7 @@ Error DWARFListTableHeader::extract(DWARFDataExtractor Data,
         SectionName.data(), HeaderOffset, HeaderData.OffsetEntryCount);
   Data.setAddressSize(HeaderData.AddrSize);
   for (uint32_t I = 0; I < HeaderData.OffsetEntryCount; ++I)
-    Offsets.push_back(Data.getU32(OffsetPtr));
+    Offsets.push_back(Data.getRelocatedValue(4, OffsetPtr));
   return Error::success();
 }
 
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFUnit.cpp b/llvm/lib/DebugInfo/DWARF/DWARFUnit.cpp
index 94bfc8c148f..b74acf60c74 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFUnit.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFUnit.cpp
@@ -241,7 +241,7 @@ bool DWARFUnitHeader::extract(DWARFContext &Context,
   IndexEntry = Entry;
   if (!IndexEntry && Index)
     IndexEntry = Index->getFromOffset(*offset_ptr);
-  Length = debug_info.getU32(offset_ptr);
+  Length = debug_info.getRelocatedValue(4, offset_ptr);
   FormParams.Format = DWARF32;
   unsigned SizeOfLength = 4;
   if (Length == 0xffffffff) {