1 files changed, 153 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/SafeStackLayout.cpp b/llvm/lib/CodeGen/SafeStackLayout.cpp
new file mode 100644
index 000000000000..09964866e4d3
--- /dev/null
+++ b/llvm/lib/CodeGen/SafeStackLayout.cpp
@@ -0,0 +1,153 @@
+//===- SafeStackLayout.cpp - SafeStack frame layout -----------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "SafeStackLayout.h"
+#include "SafeStackColoring.h"
+#include "llvm/IR/Value.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/MathExtras.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+#include <cassert>
+
+using namespace llvm;
+using namespace llvm::safestack;
+
+#define DEBUG_TYPE "safestacklayout"
+
+static cl::opt<bool> ClLayout("safe-stack-layout",
+                              cl::desc("enable safe stack layout"), cl::Hidden,
+                              cl::init(true));
+
+LLVM_DUMP_METHOD void StackLayout::print(raw_ostream &OS) {
+  OS << "Stack regions:\n";
+  for (unsigned i = 0; i < Regions.size(); ++i) {
+    OS << "  " << i << ": [" << Regions[i].Start << ", " << Regions[i].End
+       << "), range " << Regions[i].Range << "\n";
+  }
+  OS << "Stack objects:\n";
+  for (auto &IT : ObjectOffsets) {
+    OS << "  at " << IT.getSecond() << ": " << *IT.getFirst() << "\n";
+  }
+}
+
+void StackLayout::addObject(const Value *V, unsigned Size, unsigned Alignment,
+                            const StackColoring::LiveRange &Range) {
+  StackObjects.push_back({V, Size, Alignment, Range});
+  ObjectAlignments[V] = Alignment;
+  MaxAlignment = std::max(MaxAlignment, Alignment);
+}
+
+static unsigned AdjustStackOffset(unsigned Offset, unsigned Size,
+                                  unsigned Alignment) {
+  return alignTo(Offset + Size, Alignment) - Size;
+}
+
+void StackLayout::layoutObject(StackObject &Obj) {
+  if (!ClLayout) {
+    // If layout is disabled, just grab the next aligned address.
+    // This effectively disables stack coloring as well.
+    unsigned LastRegionEnd = Regions.empty() ? 0 : Regions.back().End;
+    unsigned Start = AdjustStackOffset(LastRegionEnd, Obj.Size, Obj.Alignment);
+    unsigned End = Start + Obj.Size;
+    Regions.emplace_back(Start, End, Obj.Range);
+    ObjectOffsets[Obj.Handle] = End;
+    return;
+  }
+
+  LLVM_DEBUG(dbgs() << "Layout: size " << Obj.Size << ", align "
+                    << Obj.Alignment << ", range " << Obj.Range << "\n");
+  assert(Obj.Alignment <= MaxAlignment);
+  unsigned Start = AdjustStackOffset(0, Obj.Size, Obj.Alignment);
+  unsigned End = Start + Obj.Size;
+  LLVM_DEBUG(dbgs() << "  First candidate: " << Start << " .. " << End << "\n");
+  for (const StackRegion &R : Regions) {
+    LLVM_DEBUG(dbgs() << "  Examining region: " << R.Start << " .. " << R.End
+                      << ", range " << R.Range << "\n");
+    assert(End >= R.Start);
+    if (Start >= R.End) {
+      LLVM_DEBUG(dbgs() << "  Does not intersect, skip.\n");
+      continue;
+    }
+    if (Obj.Range.Overlaps(R.Range)) {
+      // Find the next appropriate location.
+      Start = AdjustStackOffset(R.End, Obj.Size, Obj.Alignment);
+      End = Start + Obj.Size;
+      LLVM_DEBUG(dbgs() << "  Overlaps. Next candidate: " << Start << " .. "
+                        << End << "\n");
+      continue;
+    }
+    if (End <= R.End) {
+      LLVM_DEBUG(dbgs() << "  Reusing region(s).\n");
+      break;
+    }
+  }
+
+  unsigned LastRegionEnd = Regions.empty() ? 0 : Regions.back().End;
+  if (End > LastRegionEnd) {
+    // Insert a new region at the end. Maybe two.
+    if (Start > LastRegionEnd) {
+      LLVM_DEBUG(dbgs() << "  Creating gap region: " << LastRegionEnd << " .. "
+                        << Start << "\n");
+      Regions.emplace_back(LastRegionEnd, Start, StackColoring::LiveRange());
+      LastRegionEnd = Start;
+    }
+    LLVM_DEBUG(dbgs() << "  Creating new region: " << LastRegionEnd << " .. "
+                      << End << ", range " << Obj.Range << "\n");
+    Regions.emplace_back(LastRegionEnd, End, Obj.Range);
+    LastRegionEnd = End;
+  }
+
+  // Split starting and ending regions if necessary.
+  for (unsigned i = 0; i < Regions.size(); ++i) {
+    StackRegion &R = Regions[i];
+    if (Start > R.Start && Start < R.End) {
+      StackRegion R0 = R;
+      R.Start = R0.End = Start;
+      Regions.insert(&R, R0);
+      continue;
+    }
+    if (End > R.Start && End < R.End) {
+      StackRegion R0 = R;
+      R0.End = R.Start = End;
+      Regions.insert(&R, R0);
+      break;
+    }
+  }
+
+  // Update live ranges for all affected regions.
+  for (StackRegion &R : Regions) {
+    if (Start < R.End && End > R.Start)
+      R.Range.Join(Obj.Range);
+    if (End <= R.End)
+      break;
+  }
+
+  ObjectOffsets[Obj.Handle] = End;
+}
+
+void StackLayout::computeLayout() {
+  // Simple greedy algorithm.
+  // If this is replaced with something smarter, it must preserve the property
+  // that the first object is always at the offset 0 in the stack frame (for
+  // StackProtectorSlot), or handle stack protector in some other way.
+
+  // Sort objects by size (largest first) to reduce fragmentation.
+  if (StackObjects.size() > 2)
+    std::stable_sort(StackObjects.begin() + 1, StackObjects.end(),
+                     [](const StackObject &a, const StackObject &b) {
+                       return a.Size > b.Size;
+                     });
+
+  for (auto &Obj : StackObjects)
+    layoutObject(Obj);
+
+  LLVM_DEBUG(print(dbgs()));
+}