vendor/lld/lld-trunk-r233088

1 files changed, 125 insertions, 0 deletions

diff --git a/include/lld/Core/Reference.h b/include/lld/Core/Reference.h
new file mode 100644
index 000000000000..7a804c31e182
--- /dev/null
+++ b/include/lld/Core/Reference.h
@@ -0,0 +1,125 @@
+//===- Core/References.h - A Reference to Another Atom --------------------===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_CORE_REFERENCES_H
+#define LLD_CORE_REFERENCES_H
+
+#include "lld/Core/LLVM.h"
+#include "llvm/ADT/StringSwitch.h"
+
+namespace lld {
+class Atom;
+
+///
+/// The linker has a Graph Theory model of linking. An object file is seen
+/// as a set of Atoms with References to other Atoms.  Each Atom is a node
+/// and each Reference is an edge.
+///
+/// For example if a function contains a call site to "malloc" 40 bytes into
+/// the Atom, then the function Atom will have a Reference of: offsetInAtom=40,
+/// kind=callsite, target=malloc, addend=0.
+///
+/// Besides supporting traditional "relocations", References are also used
+/// grouping atoms (group comdat), forcing layout (one atom must follow
+/// another), marking data-in-code (jump tables or ARM constants), etc.
+///
+/// The "kind" of a reference is a tuple of <namespace, arch, value>.  This
+/// enable us to re-use existing relocation types definded for various
+/// file formats and architectures.  For instance, in ELF the relocation type 10
+/// means R_X86_64_32 for x86_64, and R_386_GOTPC for i386. For PE/COFF
+/// relocation 10 means IMAGE_REL_AMD64_SECTION.
+///
+/// References and atoms form a directed graph. The dead-stripping pass
+/// traverses them starting from dead-strip root atoms to garbage collect
+/// unreachable ones.
+///
+/// References of any kind are considered as directed edges. In addition to
+/// that, references of some kind is considered as bidirected edges.
+class Reference {
+public:
+  /// Which universe defines the kindValue().
+  enum class KindNamespace {
+    all     = 0,
+    testing = 1,
+    ELF     = 2,
+    COFF    = 3,
+    mach_o  = 4,
+  };
+
+  KindNamespace kindNamespace() const { return (KindNamespace)_kindNamespace; }
+  void setKindNamespace(KindNamespace ns) { _kindNamespace = (uint8_t)ns; }
+
+  // Which architecture the kind value is for.
+  enum class KindArch { all, AArch64, ARM, Hexagon, Mips, x86, x86_64 };
+
+  KindArch kindArch() const { return (KindArch)_kindArch; }
+  void setKindArch(KindArch a) { _kindArch = (uint8_t)a; }
+
+  typedef uint16_t KindValue;
+
+  KindValue kindValue() const { return _kindValue; }
+
+  /// setKindValue() is needed because during linking, some optimizations may
+  /// change the codegen and hence the reference kind.
+  void setKindValue(KindValue value) {
+    _kindValue = value;
+  }
+
+  /// KindValues used with KindNamespace::all and KindArch::all.
+  enum {
+    // kindLayoutAfter is treated as a bidirected edge by the dead-stripping
+    // pass.
+    kindLayoutAfter = 1,
+    // kindGroupChild is treated as a bidirected edge too.
+    kindGroupChild,
+    kindAssociate,
+  };
+
+  // A value to be added to the value of a target
+  typedef int64_t Addend;
+
+  /// If the reference is a fixup in the Atom, then this returns the
+  /// byte offset into the Atom's content to do the fix up.
+  virtual uint64_t offsetInAtom() const = 0;
+
+  /// Returns the atom this reference refers to.
+  virtual const Atom *target() const = 0;
+
+  /// During linking, the linker may merge graphs which coalesces some nodes
+  /// (i.e. Atoms).  To switch the target of a reference, this method is called.
+  virtual void setTarget(const Atom *) = 0;
+
+  /// Some relocations require a symbol and a value (e.g. foo + 4).
+  virtual Addend addend() const = 0;
+
+  /// During linking, some optimzations may change addend value.
+  virtual void setAddend(Addend) = 0;
+
+  /// Returns target specific attributes of the reference.
+  virtual uint32_t tag() const { return 0; }
+
+protected:
+  /// Reference is an abstract base class.  Only subclasses can use constructor.
+  Reference(KindNamespace ns, KindArch a, KindValue value)
+      : _kindValue(value), _kindNamespace((uint8_t)ns), _kindArch((uint8_t)a) {}
+
+  /// The memory for Reference objects is always managed by the owning File
+  /// object.  Therefore, no one but the owning File object should call
+  /// delete on an Reference.  In fact, some File objects may bulk allocate
+  /// an array of References, so they cannot be individually deleted by anyone.
+  virtual ~Reference() {}
+
+  KindValue  _kindValue;
+  uint8_t    _kindNamespace;
+  uint8_t    _kindArch;
+};
+
+} // namespace lld
+
+#endif // LLD_CORE_REFERENCES_H