1 files changed, 129 insertions, 0 deletions
diff --git a/gnu/llvm/tools/lld/lib/ReaderWriter/MachO/ShimPass.cpp b/gnu/llvm/tools/lld/lib/ReaderWriter/MachO/ShimPass.cpp
new file mode 100644
index 00000000000..cd536714665
--- /dev/null
+++ b/gnu/llvm/tools/lld/lib/ReaderWriter/MachO/ShimPass.cpp
@@ -0,0 +1,129 @@
+//===- lib/ReaderWriter/MachO/ShimPass.cpp -------------------------------===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This linker pass updates branch-sites whose target is a different mode
+// (thumb vs arm).
+//
+// Arm code has two instruction encodings thumb and arm.  When branching from
+// one code encoding to another, you need to use an instruction that switches
+// the instruction mode.  Usually the transition only happens at call sites, and
+// the linker can transform a BL instruction in BLX (or vice versa).  But if the
+// compiler did a tail call optimization and a function ends with a branch (not
+// branch and link), there is no pc-rel BX instruction.
+//
+// The ShimPass looks for pc-rel B instructions that will need to switch mode.
+// For those cases it synthesizes a shim which does the transition, then
+// modifies the original atom with the B instruction to target to the shim atom.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ArchHandler.h"
+#include "File.h"
+#include "MachOPasses.h"
+#include "lld/Core/DefinedAtom.h"
+#include "lld/Core/File.h"
+#include "lld/Core/LLVM.h"
+#include "lld/Core/Reference.h"
+#include "lld/Core/Simple.h"
+#include "lld/ReaderWriter/MachOLinkingContext.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/STLExtras.h"
+
+namespace lld {
+namespace mach_o {
+
+class ShimPass : public Pass {
+public:
+  ShimPass(const MachOLinkingContext &context)
+      : _ctx(context), _archHandler(_ctx.archHandler()),
+        _stubInfo(_archHandler.stubInfo()),
+        _file(*_ctx.make_file<MachOFile>("<mach-o shim pass>")) {
+    _file.setOrdinal(_ctx.getNextOrdinalAndIncrement());
+  }
+
+  llvm::Error perform(SimpleFile &mergedFile) override {
+    // Scan all references in all atoms.
+    for (const DefinedAtom *atom : mergedFile.defined()) {
+      for (const Reference *ref : *atom) {
+        // Look at non-call branches.
+        if (!_archHandler.isNonCallBranch(*ref))
+          continue;
+        const Atom *target = ref->target();
+        assert(target != nullptr);
+        if (const lld::DefinedAtom *daTarget = dyn_cast<DefinedAtom>(target)) {
+          bool atomIsThumb = _archHandler.isThumbFunction(*atom);
+          bool targetIsThumb = _archHandler.isThumbFunction(*daTarget);
+          if (atomIsThumb != targetIsThumb)
+            updateBranchToUseShim(atomIsThumb, *daTarget, ref);
+        }
+      }
+    }
+    // Exit early if no shims needed.
+    if (_targetToShim.empty())
+      return llvm::Error();
+
+    // Sort shim atoms so the layout order is stable.
+    std::vector<const DefinedAtom *> shims;
+    shims.reserve(_targetToShim.size());
+    for (auto element : _targetToShim) {
+      shims.push_back(element.second);
+    }
+    std::sort(shims.begin(), shims.end(),
+              [](const DefinedAtom *l, const DefinedAtom *r) {
+                return (l->name() < r->name());
+              });
+
+    // Add all shims to master file.
+    for (const DefinedAtom *shim : shims)
+      mergedFile.addAtom(*shim);
+
+    return llvm::Error();
+  }
+
+private:
+
+  void updateBranchToUseShim(bool thumbToArm, const DefinedAtom& target,
+                             const Reference *ref) {
+    // Make file-format specific stub and other support atoms.
+    const DefinedAtom *shim = this->getShim(thumbToArm, target);
+    assert(shim != nullptr);
+    // Switch branch site to target shim atom.
+    const_cast<Reference *>(ref)->setTarget(shim);
+  }
+
+  const DefinedAtom* getShim(bool thumbToArm, const DefinedAtom& target) {
+    auto pos = _targetToShim.find(&target);
+    if ( pos != _targetToShim.end() ) {
+      // Reuse an existing shim.
+      assert(pos->second != nullptr);
+      return pos->second;
+    } else {
+      // There is no existing shim, so create a new one.
+      const DefinedAtom *shim = _archHandler.createShim(_file, thumbToArm,
+                                                        target);
+       _targetToShim[&target] = shim;
+       return shim;
+    }
+  }
+
+  const MachOLinkingContext &_ctx;
+  mach_o::ArchHandler                            &_archHandler;
+  const ArchHandler::StubInfo                    &_stubInfo;
+  MachOFile                                      &_file;
+  llvm::DenseMap<const Atom*, const DefinedAtom*> _targetToShim;
+};
+
+
+
+void addShimPass(PassManager &pm, const MachOLinkingContext &ctx) {
+  pm.add(llvm::make_unique<ShimPass>(ctx));
+}
+
+} // end namespace mach_o
+} // end namespace lld