[PATCH] D33673: [Object/RelocVisitor] - Add support for R_X86_64_DTPOFF32 relocation.

[George Rimar via Phabricator via llvm-commits]

grimar created this revision.
Herald added a subscriber: aprantl.

This is PR33173. More simple way to reproduce is below:

If we have tls.c file with line

  __thread int a;

gcc -c tls.c -g

gives us R_X86_64_DTPOFF32 relocation in output:

  Relocation section '.rela.debug_info' at offset 0x2e0 contains 6 entries:
    Offset          Info           Type           Sym. Value    Sym. Name + Addend
  000000000006  00070000000a R_X86_64_32       0000000000000000 .debug_abbrev + 0
  00000000000c  000a0000000a R_X86_64_32       0000000000000000 .debug_str + 26
  000000000011  000a0000000a R_X86_64_32       0000000000000000 .debug_str + 54
  000000000015  000a0000000a R_X86_64_32       0000000000000000 .debug_str + 0
  000000000019  00090000000a R_X86_64_32       0000000000000000 .debug_line + 0
  000000000028  000d00000015 R_X86_64_DTPOFF32 0000000000000000 a + 0

And run of llvm-dwarfdump tls.o would report "error: failed to compute relocation: R_X86_64_DTPOFF32"
error then, because such a relocation is not supported atm.

R_X86_64_DTPOFF32 calculates negative offset in the TLS block. Problem that size of TLS segment is not known
here. The same applies for PR33173 where we use RelocVisitor as part of DWARFContextInMemory for building .gdb_index.
TLS relocations pointing to .debug_info seems useless for index building purposes and we do not care about final value too. 
So far it seems reasonable to have some value by default for TLS size, like 0 in this patch and some API that can be used in theory 
if somebody needs to evaluate those TLS relocations.

That is what this patch do.


https://reviews.llvm.org/D33673

Files:
  include/llvm/DebugInfo/DIContext.h
  include/llvm/Object/RelocVisitor.h
  lib/DebugInfo/DWARF/DWARFContext.cpp


Index: lib/DebugInfo/DWARF/DWARFContext.cpp
===================================================================
--- lib/DebugInfo/DWARF/DWARFContext.cpp
+++ lib/DebugInfo/DWARF/DWARFContext.cpp
@@ -1173,7 +1173,7 @@
         continue;
       }
 
-      object::RelocVisitor V(Obj);
+      object::RelocVisitor V(Obj, L ? L->getTlsSize() : 0);
       uint64_t Val = V.visit(Reloc.getType(), Reloc, SymInfoOrErr->Address);
       if (V.error()) {
         SmallString<32> Name;
Index: include/llvm/Object/RelocVisitor.h
===================================================================
--- include/llvm/Object/RelocVisitor.h
+++ include/llvm/Object/RelocVisitor.h
@@ -35,7 +35,8 @@
 /// @brief Base class for object file relocation visitors.
 class RelocVisitor {
 public:
-  explicit RelocVisitor(const ObjectFile &Obj) : ObjToVisit(Obj) {}
+  explicit RelocVisitor(const ObjectFile &Obj, uint64_t TlsSize)
+      : ObjToVisit(Obj), TlsSize(TlsSize) {}
 
   // TODO: Should handle multiple applied relocations via either passing in the
   // previously computed value or just count paired relocations as a single
@@ -56,6 +57,7 @@
 
 private:
   const ObjectFile &ObjToVisit;
+  uint64_t TlsSize;
   bool HasError = false;
 
   uint64_t visitELF(uint32_t Rel, RelocationRef R, uint64_t Value) {
@@ -132,6 +134,8 @@
     case ELF::R_X86_64_32:
     case ELF::R_X86_64_32S:
       return (Value + getELFAddend(R)) & 0xFFFFFFFF;
+    case ELF::R_X86_64_DTPOFF32:
+      return Value + getELFAddend(R) - TlsSize;
     }
     HasError = true;
     return 0;
Index: include/llvm/DebugInfo/DIContext.h
===================================================================
--- include/llvm/DebugInfo/DIContext.h
+++ include/llvm/DebugInfo/DIContext.h
@@ -211,6 +211,10 @@
     return false;
   }
 
+  /// Method returns size of TLS segment which is required for resolving TLS
+  /// relocations sometimes.
+  virtual uint64_t getTlsSize() const { return 0; }
+
   /// Obtain a copy of this LoadedObjectInfo.
   ///
   /// The caller is responsible for deallocation once the copy is no longer required.


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