[DWARF] Refactor RelocVisitor and fix computation of SHT_RELA-typed relocation entries

Summary:
getRelocatedValue may compute incorrect value for SHT_RELA-typed relocation entries.

// DWARFDataExtractor.cpp
uint64_t DWARFDataExtractor::getRelocatedValue(uint32_t Size, uint32_t *Off,
...
  // This formula is correct for REL, but may be incorrect for RELA if the value
  // stored in the location (getUnsigned(Off, Size)) is not zero.
  return getUnsigned(Off, Size) + Rel->Value;

In this patch, we

* refactor these visit* functions to include a new parameter `uint64_t A`.
  Since these visit* functions are no longer used as visitors, rename them to resolve*.
  + REL: A is used as the addend. A is the value stored in the location where the
    relocation applies: getUnsigned(Off, Size)
  + RELA: The addend encoded in RelocationRef is used, e.g. getELFAddend(R)
* and add another set of supports* functions to check if a given relocation type is handled.
  DWARFObjInMemory uses them to fail early.

Reviewers: echristo, dblaikie

Reviewed By: echristo

Subscribers: mgorny, aprantl, aheejin, fedor.sergeev, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D57939

llvm-svn: 356729

2 files changed, 19 insertions, 12 deletions

diff --git a/llvm/lib/DebugInfo/DWARF/DWARFContext.cpp b/llvm/lib/DebugInfo/DWARF/DWARFContext.cpp
index dc0539f4634..789874f5cbd 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFContext.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFContext.cpp
@@ -36,7 +36,7 @@
 #include "llvm/Object/Decompressor.h"
 #include "llvm/Object/MachO.h"
 #include "llvm/Object/ObjectFile.h"
-#include "llvm/Object/RelocVisitor.h"
+#include "llvm/Object/RelocationResolver.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/DataExtractor.h"
 #include "llvm/Support/Error.h"
@@ -1500,6 +1500,9 @@ public:
 
       // Symbol to [address, section index] cache mapping.
       std::map<SymbolRef, SymInfo> AddrCache;
+      bool (*Supports)(uint64_t);
+      RelocationResolver Resolver;
+      std::tie(Supports, Resolver) = getRelocationResolver(Obj);
       for (const RelocationRef &Reloc : Section.relocations()) {
         // FIXME: it's not clear how to correctly handle scattered
         // relocations.
@@ -1514,9 +1517,15 @@ public:
           continue;
         }
 
-        object::RelocVisitor V(Obj);
-        uint64_t Val = V.visit(Reloc.getType(), Reloc, SymInfoOrErr->Address);
-        if (V.error()) {
+        // Check if Resolver can handle this relocation type early so as not to
+        // handle invalid cases in DWARFDataExtractor.
+        //
+        // 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});
+        } else {
           SmallString<32> Type;
           Reloc.getTypeName(Type);
           ErrorPolicy EP = HandleError(
@@ -1524,10 +1533,7 @@ public:
                           errorCodeToError(object_error::parse_failed)));
           if (EP == ErrorPolicy::Halt)
             return;
-          continue;
         }
-        RelocAddrEntry Rel = {SymInfoOrErr->SectionIndex, Val};
-        Map->insert({Reloc.getOffset(), Rel});
       }
     }
 
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFDataExtractor.cpp b/llvm/lib/DebugInfo/DWARF/DWARFDataExtractor.cpp
index bd8c23765e4..6f2f992f53e 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFDataExtractor.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFDataExtractor.cpp
@@ -18,12 +18,13 @@ uint64_t DWARFDataExtractor::getRelocatedValue(uint32_t Size, uint32_t *Off,
     *SecNdx = object::SectionedAddress::UndefSection;
   if (!Section)
     return getUnsigned(Off, Size);
-  Optional<RelocAddrEntry> Rel = Obj->find(*Section, *Off);
-  if (!Rel)
-    return getUnsigned(Off, Size);
+  Optional<RelocAddrEntry> E = Obj->find(*Section, *Off);
+  uint64_t A = getUnsigned(Off, Size);
+  if (!E)
+    return A;
   if (SecNdx)
-    *SecNdx = Rel->SectionIndex;
-  return getUnsigned(Off, Size) + Rel->Value;
+    *SecNdx = E->SectionIndex;
+  return E->Resolver(E->Reloc, E->SymbolValue, A);
 }
 
 Optional<uint64_t>