[RuntimeDyldELF] Improve GOT support

Summary:
This is the first in a series of patches to eventually add support for TLS relocations to RuntimeDyld. This patch resolves an issue in the current GOT handling, where GOT entries would be reused between object files, which leads to the same situation that necessitates the GOT in the first place, i.e. that the 32-bit offset can not cover all of the address space. Thus this patch makes the GOT object-file-local.
Unfortunately, this still isn't quite enough, because the MemoryManager does not yet guarantee that sections are allocated sufficiently close to each other, even if they belong to the same object file. To address this concern, this patch also adds a small API abstraction on top of the GOT allocation mechanism that will allow (temporarily, until the MemoryManager is improved) using the stub mechanism instead of allocating a different section. The actual switch from separate section to stub mechanism will be part of a follow-on commit, so that it can be easily reverted independently at the appropriate time.

Test Plan: Includes a test case where the GOT of two object files is artificially forced to be apart by several GB.

Reviewers: lhames

Reviewed By: lhames

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D8813

llvm-svn: 234839

1 files changed, 23 insertions, 7 deletions

diff --git a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.h b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.h
index a3ffa3d0beb..590d26a3fb8 100644
--- a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.h
+++ b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.h
@@ -80,16 +80,32 @@ class RuntimeDyldELF : public RuntimeDyldImpl {
                            ObjSectionToIDMap &LocalSections,
                            RelocationValueRef &Rel);
 
-  uint64_t findGOTEntry(uint64_t LoadAddr, uint64_t Offset);
   size_t getGOTEntrySize();
 
-  void updateGOTEntries(StringRef Name, uint64_t Addr) override;
+  SectionEntry &getSection(unsigned SectionID) { return Sections[SectionID]; }
 
-  // Relocation entries for symbols whose position-independent offset is
-  // updated in a global offset table.
-  typedef SmallVector<RelocationValueRef, 2> GOTRelocations;
-  GOTRelocations GOTEntries; // List of entries requiring finalization.
-  SmallVector<std::pair<SID, GOTRelocations>, 8> GOTs; // Allocated tables.
+  // Allocate no GOT entries for use in the given section.
+  uint64_t allocateGOTEntries(unsigned SectionID, unsigned no);
+
+  // Resolve the relvative address of GOTOffset in Section ID and place
+  // it at the given Offset
+  void resolveGOTOffsetRelocation(unsigned SectionID, uint64_t Offset,
+                                  uint64_t GOTOffset);
+
+  // For a GOT entry referenced from SectionID, compute a relocation entry
+  // that will place the final resolved value in the GOT slot
+  RelocationEntry computeGOTOffsetRE(unsigned SectionID,
+                                     uint64_t GOTOffset,
+                                     uint64_t SymbolOffset,
+                                     unsigned Type);
+
+  // The tentative ID for the GOT section
+  unsigned GOTSectionID;
+
+  // Records the current number of allocated slots in the GOT
+  // (This would be equivalent to GOTEntries.size() were it not for relocations
+  // that consume more than one slot)
+  unsigned CurrentGOTIndex;
 
   // When a module is loaded we save the SectionID of the EH frame section
   // in a table until we receive a request to register all unregistered