Bug Summary

File:lib/CodeGen/SafeStack.cpp
Warning:line 595, column 7
Value stored to 'Size' is never read

Annotated Source Code

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clang -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name SafeStack.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -mrelocation-model pic -pic-level 2 -mthread-model posix -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -dwarf-column-info -debugger-tuning=gdb -momit-leaf-frame-pointer -ffunction-sections -fdata-sections -resource-dir /usr/lib/llvm-8/lib/clang/8.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-8~svn345461/build-llvm/lib/CodeGen -I /build/llvm-toolchain-snapshot-8~svn345461/lib/CodeGen -I /build/llvm-toolchain-snapshot-8~svn345461/build-llvm/include -I /build/llvm-toolchain-snapshot-8~svn345461/include -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0/backward -internal-isystem /usr/include/clang/8.0.0/include/ -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-8/lib/clang/8.0.0/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-comment -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /build/llvm-toolchain-snapshot-8~svn345461/build-llvm/lib/CodeGen -ferror-limit 19 -fmessage-length 0 -fvisibility-inlines-hidden -fobjc-runtime=gcc -fdiagnostics-show-option -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -o /tmp/scan-build-2018-10-27-211344-32123-1 -x c++ /build/llvm-toolchain-snapshot-8~svn345461/lib/CodeGen/SafeStack.cpp -faddrsig
1//===- SafeStack.cpp - Safe Stack Insertion -------------------------------===//
2//
3// The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This pass splits the stack into the safe stack (kept as-is for LLVM backend)
11// and the unsafe stack (explicitly allocated and managed through the runtime
12// support library).
13//
14// http://clang.llvm.org/docs/SafeStack.html
15//
16//===----------------------------------------------------------------------===//
17
18#include "SafeStackColoring.h"
19#include "SafeStackLayout.h"
20#include "llvm/ADT/APInt.h"
21#include "llvm/ADT/ArrayRef.h"
22#include "llvm/ADT/SmallPtrSet.h"
23#include "llvm/ADT/SmallVector.h"
24#include "llvm/ADT/Statistic.h"
25#include "llvm/Analysis/AssumptionCache.h"
26#include "llvm/Analysis/BranchProbabilityInfo.h"
27#include "llvm/Analysis/InlineCost.h"
28#include "llvm/Analysis/LoopInfo.h"
29#include "llvm/Analysis/ScalarEvolution.h"
30#include "llvm/Analysis/ScalarEvolutionExpressions.h"
31#include "llvm/Analysis/TargetLibraryInfo.h"
32#include "llvm/Transforms/Utils/Local.h"
33#include "llvm/CodeGen/TargetLowering.h"
34#include "llvm/CodeGen/TargetPassConfig.h"
35#include "llvm/CodeGen/TargetSubtargetInfo.h"
36#include "llvm/IR/Argument.h"
37#include "llvm/IR/Attributes.h"
38#include "llvm/IR/CallSite.h"
39#include "llvm/IR/ConstantRange.h"
40#include "llvm/IR/Constants.h"
41#include "llvm/IR/DIBuilder.h"
42#include "llvm/IR/DataLayout.h"
43#include "llvm/IR/DerivedTypes.h"
44#include "llvm/IR/Dominators.h"
45#include "llvm/IR/Function.h"
46#include "llvm/IR/IRBuilder.h"
47#include "llvm/IR/InstIterator.h"
48#include "llvm/IR/Instruction.h"
49#include "llvm/IR/Instructions.h"
50#include "llvm/IR/IntrinsicInst.h"
51#include "llvm/IR/Intrinsics.h"
52#include "llvm/IR/MDBuilder.h"
53#include "llvm/IR/Module.h"
54#include "llvm/IR/Type.h"
55#include "llvm/IR/Use.h"
56#include "llvm/IR/User.h"
57#include "llvm/IR/Value.h"
58#include "llvm/Pass.h"
59#include "llvm/Support/Casting.h"
60#include "llvm/Support/Debug.h"
61#include "llvm/Support/ErrorHandling.h"
62#include "llvm/Support/MathExtras.h"
63#include "llvm/Support/raw_ostream.h"
64#include "llvm/Target/TargetMachine.h"
65#include "llvm/Transforms/Utils/BasicBlockUtils.h"
66#include "llvm/Transforms/Utils/Cloning.h"
67#include <algorithm>
68#include <cassert>
69#include <cstdint>
70#include <string>
71#include <utility>
72
73using namespace llvm;
74using namespace llvm::safestack;
75
76#define DEBUG_TYPE"safe-stack" "safe-stack"
77
78namespace llvm {
79
80STATISTIC(NumFunctions, "Total number of functions")static llvm::Statistic NumFunctions = {"safe-stack", "NumFunctions"
, "Total number of functions", {0}, {false}}
;
81STATISTIC(NumUnsafeStackFunctions, "Number of functions with unsafe stack")static llvm::Statistic NumUnsafeStackFunctions = {"safe-stack"
, "NumUnsafeStackFunctions", "Number of functions with unsafe stack"
, {0}, {false}}
;
82STATISTIC(NumUnsafeStackRestorePointsFunctions,static llvm::Statistic NumUnsafeStackRestorePointsFunctions =
{"safe-stack", "NumUnsafeStackRestorePointsFunctions", "Number of functions that use setjmp or exceptions"
, {0}, {false}}
83 "Number of functions that use setjmp or exceptions")static llvm::Statistic NumUnsafeStackRestorePointsFunctions =
{"safe-stack", "NumUnsafeStackRestorePointsFunctions", "Number of functions that use setjmp or exceptions"
, {0}, {false}}
;
84
85STATISTIC(NumAllocas, "Total number of allocas")static llvm::Statistic NumAllocas = {"safe-stack", "NumAllocas"
, "Total number of allocas", {0}, {false}}
;
86STATISTIC(NumUnsafeStaticAllocas, "Number of unsafe static allocas")static llvm::Statistic NumUnsafeStaticAllocas = {"safe-stack"
, "NumUnsafeStaticAllocas", "Number of unsafe static allocas"
, {0}, {false}}
;
87STATISTIC(NumUnsafeDynamicAllocas, "Number of unsafe dynamic allocas")static llvm::Statistic NumUnsafeDynamicAllocas = {"safe-stack"
, "NumUnsafeDynamicAllocas", "Number of unsafe dynamic allocas"
, {0}, {false}}
;
88STATISTIC(NumUnsafeByValArguments, "Number of unsafe byval arguments")static llvm::Statistic NumUnsafeByValArguments = {"safe-stack"
, "NumUnsafeByValArguments", "Number of unsafe byval arguments"
, {0}, {false}}
;
89STATISTIC(NumUnsafeStackRestorePoints, "Number of setjmps and landingpads")static llvm::Statistic NumUnsafeStackRestorePoints = {"safe-stack"
, "NumUnsafeStackRestorePoints", "Number of setjmps and landingpads"
, {0}, {false}}
;
90
91} // namespace llvm
92
93/// Use __safestack_pointer_address even if the platform has a faster way of
94/// access safe stack pointer.
95static cl::opt<bool>
96 SafeStackUsePointerAddress("safestack-use-pointer-address",
97 cl::init(false), cl::Hidden);
98
99
100namespace {
101
102/// Rewrite an SCEV expression for a memory access address to an expression that
103/// represents offset from the given alloca.
104///
105/// The implementation simply replaces all mentions of the alloca with zero.
106class AllocaOffsetRewriter : public SCEVRewriteVisitor<AllocaOffsetRewriter> {
107 const Value *AllocaPtr;
108
109public:
110 AllocaOffsetRewriter(ScalarEvolution &SE, const Value *AllocaPtr)
111 : SCEVRewriteVisitor(SE), AllocaPtr(AllocaPtr) {}
112
113 const SCEV *visitUnknown(const SCEVUnknown *Expr) {
114 if (Expr->getValue() == AllocaPtr)
115 return SE.getZero(Expr->getType());
116 return Expr;
117 }
118};
119
120/// The SafeStack pass splits the stack of each function into the safe
121/// stack, which is only accessed through memory safe dereferences (as
122/// determined statically), and the unsafe stack, which contains all
123/// local variables that are accessed in ways that we can't prove to
124/// be safe.
125class SafeStack {
126 Function &F;
127 const TargetLoweringBase &TL;
128 const DataLayout &DL;
129 ScalarEvolution &SE;
130
131 Type *StackPtrTy;
132 Type *IntPtrTy;
133 Type *Int32Ty;
134 Type *Int8Ty;
135
136 Value *UnsafeStackPtr = nullptr;
137
138 /// Unsafe stack alignment. Each stack frame must ensure that the stack is
139 /// aligned to this value. We need to re-align the unsafe stack if the
140 /// alignment of any object on the stack exceeds this value.
141 ///
142 /// 16 seems like a reasonable upper bound on the alignment of objects that we
143 /// might expect to appear on the stack on most common targets.
144 enum { StackAlignment = 16 };
145
146 /// Return the value of the stack canary.
147 Value *getStackGuard(IRBuilder<> &IRB, Function &F);
148
149 /// Load stack guard from the frame and check if it has changed.
150 void checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &RI,
151 AllocaInst *StackGuardSlot, Value *StackGuard);
152
153 /// Find all static allocas, dynamic allocas, return instructions and
154 /// stack restore points (exception unwind blocks and setjmp calls) in the
155 /// given function and append them to the respective vectors.
156 void findInsts(Function &F, SmallVectorImpl<AllocaInst *> &StaticAllocas,
157 SmallVectorImpl<AllocaInst *> &DynamicAllocas,
158 SmallVectorImpl<Argument *> &ByValArguments,
159 SmallVectorImpl<ReturnInst *> &Returns,
160 SmallVectorImpl<Instruction *> &StackRestorePoints);
161
162 /// Calculate the allocation size of a given alloca. Returns 0 if the
163 /// size can not be statically determined.
164 uint64_t getStaticAllocaAllocationSize(const AllocaInst* AI);
165
166 /// Allocate space for all static allocas in \p StaticAllocas,
167 /// replace allocas with pointers into the unsafe stack and generate code to
168 /// restore the stack pointer before all return instructions in \p Returns.
169 ///
170 /// \returns A pointer to the top of the unsafe stack after all unsafe static
171 /// allocas are allocated.
172 Value *moveStaticAllocasToUnsafeStack(IRBuilder<> &IRB, Function &F,
173 ArrayRef<AllocaInst *> StaticAllocas,
174 ArrayRef<Argument *> ByValArguments,
175 ArrayRef<ReturnInst *> Returns,
176 Instruction *BasePointer,
177 AllocaInst *StackGuardSlot);
178
179 /// Generate code to restore the stack after all stack restore points
180 /// in \p StackRestorePoints.
181 ///
182 /// \returns A local variable in which to maintain the dynamic top of the
183 /// unsafe stack if needed.
184 AllocaInst *
185 createStackRestorePoints(IRBuilder<> &IRB, Function &F,
186 ArrayRef<Instruction *> StackRestorePoints,
187 Value *StaticTop, bool NeedDynamicTop);
188
189 /// Replace all allocas in \p DynamicAllocas with code to allocate
190 /// space dynamically on the unsafe stack and store the dynamic unsafe stack
191 /// top to \p DynamicTop if non-null.
192 void moveDynamicAllocasToUnsafeStack(Function &F, Value *UnsafeStackPtr,
193 AllocaInst *DynamicTop,
194 ArrayRef<AllocaInst *> DynamicAllocas);
195
196 bool IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize);
197
198 bool IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
199 const Value *AllocaPtr, uint64_t AllocaSize);
200 bool IsAccessSafe(Value *Addr, uint64_t Size, const Value *AllocaPtr,
201 uint64_t AllocaSize);
202
203 bool ShouldInlinePointerAddress(CallSite &CS);
204 void TryInlinePointerAddress();
205
206public:
207 SafeStack(Function &F, const TargetLoweringBase &TL, const DataLayout &DL,
208 ScalarEvolution &SE)
209 : F(F), TL(TL), DL(DL), SE(SE),
210 StackPtrTy(Type::getInt8PtrTy(F.getContext())),
211 IntPtrTy(DL.getIntPtrType(F.getContext())),
212 Int32Ty(Type::getInt32Ty(F.getContext())),
213 Int8Ty(Type::getInt8Ty(F.getContext())) {}
214
215 // Run the transformation on the associated function.
216 // Returns whether the function was changed.
217 bool run();
218};
219
220uint64_t SafeStack::getStaticAllocaAllocationSize(const AllocaInst* AI) {
221 uint64_t Size = DL.getTypeAllocSize(AI->getAllocatedType());
222 if (AI->isArrayAllocation()) {
223 auto C = dyn_cast<ConstantInt>(AI->getArraySize());
224 if (!C)
225 return 0;
226 Size *= C->getZExtValue();
227 }
228 return Size;
229}
230
231bool SafeStack::IsAccessSafe(Value *Addr, uint64_t AccessSize,
232 const Value *AllocaPtr, uint64_t AllocaSize) {
233 AllocaOffsetRewriter Rewriter(SE, AllocaPtr);
234 const SCEV *Expr = Rewriter.visit(SE.getSCEV(Addr));
235
236 uint64_t BitWidth = SE.getTypeSizeInBits(Expr->getType());
237 ConstantRange AccessStartRange = SE.getUnsignedRange(Expr);
238 ConstantRange SizeRange =
239 ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AccessSize));
240 ConstantRange AccessRange = AccessStartRange.add(SizeRange);
241 ConstantRange AllocaRange =
242 ConstantRange(APInt(BitWidth, 0), APInt(BitWidth, AllocaSize));
243 bool Safe = AllocaRange.contains(AccessRange);
244
245 LLVM_DEBUG(do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
246 dbgs() << "[SafeStack] "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
247 << (isa<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
248 << *AllocaPtr << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
249 << " Access " << *Addr << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
250 << " SCEV " << *Exprdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
251 << " U: " << SE.getUnsignedRange(Expr)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
252 << ", S: " << SE.getSignedRange(Expr) << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
253 << " Range " << AccessRange << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
254 << " AllocaRange " << AllocaRange << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
255 << " " << (Safe ? "safe" : "unsafe") << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] " << (isa
<AllocaInst>(AllocaPtr) ? "Alloca " : "ByValArgument ")
<< *AllocaPtr << "\n" << " Access "
<< *Addr << "\n" << " SCEV " <<
*Expr << " U: " << SE.getUnsignedRange(Expr) <<
", S: " << SE.getSignedRange(Expr) << "\n" <<
" Range " << AccessRange << "\n" <<
" AllocaRange " << AllocaRange << "\n"
<< " " << (Safe ? "safe" : "unsafe") <<
"\n"; } } while (false)
;
256
257 return Safe;
258}
259
260bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
261 const Value *AllocaPtr,
262 uint64_t AllocaSize) {
263 if (auto MTI = dyn_cast<MemTransferInst>(MI)) {
264 if (MTI->getRawSource() != U && MTI->getRawDest() != U)
265 return true;
266 } else {
267 if (MI->getRawDest() != U)
268 return true;
269 }
270
271 const auto *Len = dyn_cast<ConstantInt>(MI->getLength());
272 // Non-constant size => unsafe. FIXME: try SCEV getRange.
273 if (!Len) return false;
274 return IsAccessSafe(U, Len->getZExtValue(), AllocaPtr, AllocaSize);
275}
276
277/// Check whether a given allocation must be put on the safe
278/// stack or not. The function analyzes all uses of AI and checks whether it is
279/// only accessed in a memory safe way (as decided statically).
280bool SafeStack::IsSafeStackAlloca(const Value *AllocaPtr, uint64_t AllocaSize) {
281 // Go through all uses of this alloca and check whether all accesses to the
282 // allocated object are statically known to be memory safe and, hence, the
283 // object can be placed on the safe stack.
284 SmallPtrSet<const Value *, 16> Visited;
285 SmallVector<const Value *, 8> WorkList;
286 WorkList.push_back(AllocaPtr);
287
288 // A DFS search through all uses of the alloca in bitcasts/PHI/GEPs/etc.
289 while (!WorkList.empty()) {
290 const Value *V = WorkList.pop_back_val();
291 for (const Use &UI : V->uses()) {
292 auto I = cast<const Instruction>(UI.getUser());
293 assert(V == UI.get())((V == UI.get()) ? static_cast<void> (0) : __assert_fail
("V == UI.get()", "/build/llvm-toolchain-snapshot-8~svn345461/lib/CodeGen/SafeStack.cpp"
, 293, __PRETTY_FUNCTION__))
;
294
295 switch (I->getOpcode()) {
296 case Instruction::Load:
297 if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getType()), AllocaPtr,
298 AllocaSize))
299 return false;
300 break;
301
302 case Instruction::VAArg:
303 // "va-arg" from a pointer is safe.
304 break;
305 case Instruction::Store:
306 if (V == I->getOperand(0)) {
307 // Stored the pointer - conservatively assume it may be unsafe.
308 LLVM_DEBUG(dbgs()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Unsafe alloca: "
<< *AllocaPtr << "\n store of address: "
<< *I << "\n"; } } while (false)
309 << "[SafeStack] Unsafe alloca: " << *AllocaPtrdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Unsafe alloca: "
<< *AllocaPtr << "\n store of address: "
<< *I << "\n"; } } while (false)
310 << "\n store of address: " << *I << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Unsafe alloca: "
<< *AllocaPtr << "\n store of address: "
<< *I << "\n"; } } while (false)
;
311 return false;
312 }
313
314 if (!IsAccessSafe(UI, DL.getTypeStoreSize(I->getOperand(0)->getType()),
315 AllocaPtr, AllocaSize))
316 return false;
317 break;
318
319 case Instruction::Ret:
320 // Information leak.
321 return false;
322
323 case Instruction::Call:
324 case Instruction::Invoke: {
325 ImmutableCallSite CS(I);
326
327 if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
328 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
329 II->getIntrinsicID() == Intrinsic::lifetime_end)
330 continue;
331 }
332
333 if (const MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
334 if (!IsMemIntrinsicSafe(MI, UI, AllocaPtr, AllocaSize)) {
335 LLVM_DEBUG(dbgs()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Unsafe alloca: "
<< *AllocaPtr << "\n unsafe memintrinsic: "
<< *I << "\n"; } } while (false)
336 << "[SafeStack] Unsafe alloca: " << *AllocaPtrdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Unsafe alloca: "
<< *AllocaPtr << "\n unsafe memintrinsic: "
<< *I << "\n"; } } while (false)
337 << "\n unsafe memintrinsic: " << *I << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Unsafe alloca: "
<< *AllocaPtr << "\n unsafe memintrinsic: "
<< *I << "\n"; } } while (false)
;
338 return false;
339 }
340 continue;
341 }
342
343 // LLVM 'nocapture' attribute is only set for arguments whose address
344 // is not stored, passed around, or used in any other non-trivial way.
345 // We assume that passing a pointer to an object as a 'nocapture
346 // readnone' argument is safe.
347 // FIXME: a more precise solution would require an interprocedural
348 // analysis here, which would look at all uses of an argument inside
349 // the function being called.
350 ImmutableCallSite::arg_iterator B = CS.arg_begin(), E = CS.arg_end();
351 for (ImmutableCallSite::arg_iterator A = B; A != E; ++A)
352 if (A->get() == V)
353 if (!(CS.doesNotCapture(A - B) && (CS.doesNotAccessMemory(A - B) ||
354 CS.doesNotAccessMemory()))) {
355 LLVM_DEBUG(dbgs() << "[SafeStack] Unsafe alloca: " << *AllocaPtrdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Unsafe alloca: "
<< *AllocaPtr << "\n unsafe call: " <<
*I << "\n"; } } while (false)
356 << "\n unsafe call: " << *I << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Unsafe alloca: "
<< *AllocaPtr << "\n unsafe call: " <<
*I << "\n"; } } while (false)
;
357 return false;
358 }
359 continue;
360 }
361
362 default:
363 if (Visited.insert(I).second)
364 WorkList.push_back(cast<const Instruction>(I));
365 }
366 }
367 }
368
369 // All uses of the alloca are safe, we can place it on the safe stack.
370 return true;
371}
372
373Value *SafeStack::getStackGuard(IRBuilder<> &IRB, Function &F) {
374 Value *StackGuardVar = TL.getIRStackGuard(IRB);
375 if (!StackGuardVar)
376 StackGuardVar =
377 F.getParent()->getOrInsertGlobal("__stack_chk_guard", StackPtrTy);
378 return IRB.CreateLoad(StackGuardVar, "StackGuard");
379}
380
381void SafeStack::findInsts(Function &F,
382 SmallVectorImpl<AllocaInst *> &StaticAllocas,
383 SmallVectorImpl<AllocaInst *> &DynamicAllocas,
384 SmallVectorImpl<Argument *> &ByValArguments,
385 SmallVectorImpl<ReturnInst *> &Returns,
386 SmallVectorImpl<Instruction *> &StackRestorePoints) {
387 for (Instruction &I : instructions(&F)) {
388 if (auto AI = dyn_cast<AllocaInst>(&I)) {
389 ++NumAllocas;
390
391 uint64_t Size = getStaticAllocaAllocationSize(AI);
392 if (IsSafeStackAlloca(AI, Size))
393 continue;
394
395 if (AI->isStaticAlloca()) {
396 ++NumUnsafeStaticAllocas;
397 StaticAllocas.push_back(AI);
398 } else {
399 ++NumUnsafeDynamicAllocas;
400 DynamicAllocas.push_back(AI);
401 }
402 } else if (auto RI = dyn_cast<ReturnInst>(&I)) {
403 Returns.push_back(RI);
404 } else if (auto CI = dyn_cast<CallInst>(&I)) {
405 // setjmps require stack restore.
406 if (CI->getCalledFunction() && CI->canReturnTwice())
407 StackRestorePoints.push_back(CI);
408 } else if (auto LP = dyn_cast<LandingPadInst>(&I)) {
409 // Exception landing pads require stack restore.
410 StackRestorePoints.push_back(LP);
411 } else if (auto II = dyn_cast<IntrinsicInst>(&I)) {
412 if (II->getIntrinsicID() == Intrinsic::gcroot)
413 report_fatal_error(
414 "gcroot intrinsic not compatible with safestack attribute");
415 }
416 }
417 for (Argument &Arg : F.args()) {
418 if (!Arg.hasByValAttr())
419 continue;
420 uint64_t Size =
421 DL.getTypeStoreSize(Arg.getType()->getPointerElementType());
422 if (IsSafeStackAlloca(&Arg, Size))
423 continue;
424
425 ++NumUnsafeByValArguments;
426 ByValArguments.push_back(&Arg);
427 }
428}
429
430AllocaInst *
431SafeStack::createStackRestorePoints(IRBuilder<> &IRB, Function &F,
432 ArrayRef<Instruction *> StackRestorePoints,
433 Value *StaticTop, bool NeedDynamicTop) {
434 assert(StaticTop && "The stack top isn't set.")((StaticTop && "The stack top isn't set.") ? static_cast
<void> (0) : __assert_fail ("StaticTop && \"The stack top isn't set.\""
, "/build/llvm-toolchain-snapshot-8~svn345461/lib/CodeGen/SafeStack.cpp"
, 434, __PRETTY_FUNCTION__))
;
435
436 if (StackRestorePoints.empty())
437 return nullptr;
438
439 // We need the current value of the shadow stack pointer to restore
440 // after longjmp or exception catching.
441
442 // FIXME: On some platforms this could be handled by the longjmp/exception
443 // runtime itself.
444
445 AllocaInst *DynamicTop = nullptr;
446 if (NeedDynamicTop) {
447 // If we also have dynamic alloca's, the stack pointer value changes
448 // throughout the function. For now we store it in an alloca.
449 DynamicTop = IRB.CreateAlloca(StackPtrTy, /*ArraySize=*/nullptr,
450 "unsafe_stack_dynamic_ptr");
451 IRB.CreateStore(StaticTop, DynamicTop);
452 }
453
454 // Restore current stack pointer after longjmp/exception catch.
455 for (Instruction *I : StackRestorePoints) {
456 ++NumUnsafeStackRestorePoints;
457
458 IRB.SetInsertPoint(I->getNextNode());
459 Value *CurrentTop = DynamicTop ? IRB.CreateLoad(DynamicTop) : StaticTop;
460 IRB.CreateStore(CurrentTop, UnsafeStackPtr);
461 }
462
463 return DynamicTop;
464}
465
466void SafeStack::checkStackGuard(IRBuilder<> &IRB, Function &F, ReturnInst &RI,
467 AllocaInst *StackGuardSlot, Value *StackGuard) {
468 Value *V = IRB.CreateLoad(StackGuardSlot);
469 Value *Cmp = IRB.CreateICmpNE(StackGuard, V);
470
471 auto SuccessProb = BranchProbabilityInfo::getBranchProbStackProtector(true);
472 auto FailureProb = BranchProbabilityInfo::getBranchProbStackProtector(false);
473 MDNode *Weights = MDBuilder(F.getContext())
474 .createBranchWeights(SuccessProb.getNumerator(),
475 FailureProb.getNumerator());
476 Instruction *CheckTerm =
477 SplitBlockAndInsertIfThen(Cmp, &RI,
478 /* Unreachable */ true, Weights);
479 IRBuilder<> IRBFail(CheckTerm);
480 // FIXME: respect -fsanitize-trap / -ftrap-function here?
481 Constant *StackChkFail = F.getParent()->getOrInsertFunction(
482 "__stack_chk_fail", IRB.getVoidTy());
483 IRBFail.CreateCall(StackChkFail, {});
484}
485
486/// We explicitly compute and set the unsafe stack layout for all unsafe
487/// static alloca instructions. We save the unsafe "base pointer" in the
488/// prologue into a local variable and restore it in the epilogue.
489Value *SafeStack::moveStaticAllocasToUnsafeStack(
490 IRBuilder<> &IRB, Function &F, ArrayRef<AllocaInst *> StaticAllocas,
491 ArrayRef<Argument *> ByValArguments, ArrayRef<ReturnInst *> Returns,
492 Instruction *BasePointer, AllocaInst *StackGuardSlot) {
493 if (StaticAllocas.empty() && ByValArguments.empty())
494 return BasePointer;
495
496 DIBuilder DIB(*F.getParent());
497
498 StackColoring SSC(F, StaticAllocas);
499 SSC.run();
500 SSC.removeAllMarkers();
501
502 // Unsafe stack always grows down.
503 StackLayout SSL(StackAlignment);
504 if (StackGuardSlot) {
505 Type *Ty = StackGuardSlot->getAllocatedType();
506 unsigned Align =
507 std::max(DL.getPrefTypeAlignment(Ty), StackGuardSlot->getAlignment());
508 SSL.addObject(StackGuardSlot, getStaticAllocaAllocationSize(StackGuardSlot),
509 Align, SSC.getFullLiveRange());
510 }
511
512 for (Argument *Arg : ByValArguments) {
513 Type *Ty = Arg->getType()->getPointerElementType();
514 uint64_t Size = DL.getTypeStoreSize(Ty);
515 if (Size == 0)
516 Size = 1; // Don't create zero-sized stack objects.
517
518 // Ensure the object is properly aligned.
519 unsigned Align = std::max((unsigned)DL.getPrefTypeAlignment(Ty),
520 Arg->getParamAlignment());
521 SSL.addObject(Arg, Size, Align, SSC.getFullLiveRange());
522 }
523
524 for (AllocaInst *AI : StaticAllocas) {
525 Type *Ty = AI->getAllocatedType();
526 uint64_t Size = getStaticAllocaAllocationSize(AI);
527 if (Size == 0)
528 Size = 1; // Don't create zero-sized stack objects.
529
530 // Ensure the object is properly aligned.
531 unsigned Align =
532 std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment());
533
534 SSL.addObject(AI, Size, Align, SSC.getLiveRange(AI));
535 }
536
537 SSL.computeLayout();
538 unsigned FrameAlignment = SSL.getFrameAlignment();
539
540 // FIXME: tell SSL that we start at a less-then-MaxAlignment aligned location
541 // (AlignmentSkew).
542 if (FrameAlignment > StackAlignment) {
543 // Re-align the base pointer according to the max requested alignment.
544 assert(isPowerOf2_32(FrameAlignment))((isPowerOf2_32(FrameAlignment)) ? static_cast<void> (0
) : __assert_fail ("isPowerOf2_32(FrameAlignment)", "/build/llvm-toolchain-snapshot-8~svn345461/lib/CodeGen/SafeStack.cpp"
, 544, __PRETTY_FUNCTION__))
;
545 IRB.SetInsertPoint(BasePointer->getNextNode());
546 BasePointer = cast<Instruction>(IRB.CreateIntToPtr(
547 IRB.CreateAnd(IRB.CreatePtrToInt(BasePointer, IntPtrTy),
548 ConstantInt::get(IntPtrTy, ~uint64_t(FrameAlignment - 1))),
549 StackPtrTy));
550 }
551
552 IRB.SetInsertPoint(BasePointer->getNextNode());
553
554 if (StackGuardSlot) {
555 unsigned Offset = SSL.getObjectOffset(StackGuardSlot);
556 Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8*
557 ConstantInt::get(Int32Ty, -Offset));
558 Value *NewAI =
559 IRB.CreateBitCast(Off, StackGuardSlot->getType(), "StackGuardSlot");
560
561 // Replace alloc with the new location.
562 StackGuardSlot->replaceAllUsesWith(NewAI);
563 StackGuardSlot->eraseFromParent();
564 }
565
566 for (Argument *Arg : ByValArguments) {
567 unsigned Offset = SSL.getObjectOffset(Arg);
568 unsigned Align = SSL.getObjectAlignment(Arg);
569 Type *Ty = Arg->getType()->getPointerElementType();
570
571 uint64_t Size = DL.getTypeStoreSize(Ty);
572 if (Size == 0)
573 Size = 1; // Don't create zero-sized stack objects.
574
575 Value *Off = IRB.CreateGEP(BasePointer, // BasePointer is i8*
576 ConstantInt::get(Int32Ty, -Offset));
577 Value *NewArg = IRB.CreateBitCast(Off, Arg->getType(),
578 Arg->getName() + ".unsafe-byval");
579
580 // Replace alloc with the new location.
581 replaceDbgDeclare(Arg, BasePointer, BasePointer->getNextNode(), DIB,
582 DIExpression::NoDeref, -Offset, DIExpression::NoDeref);
583 Arg->replaceAllUsesWith(NewArg);
584 IRB.SetInsertPoint(cast<Instruction>(NewArg)->getNextNode());
585 IRB.CreateMemCpy(Off, Align, Arg, Arg->getParamAlignment(), Size);
586 }
587
588 // Allocate space for every unsafe static AllocaInst on the unsafe stack.
589 for (AllocaInst *AI : StaticAllocas) {
590 IRB.SetInsertPoint(AI);
591 unsigned Offset = SSL.getObjectOffset(AI);
592
593 uint64_t Size = getStaticAllocaAllocationSize(AI);
594 if (Size == 0)
595 Size = 1; // Don't create zero-sized stack objects.
Value stored to 'Size' is never read
596
597 replaceDbgDeclareForAlloca(AI, BasePointer, DIB, DIExpression::NoDeref,
598 -Offset, DIExpression::NoDeref);
599 replaceDbgValueForAlloca(AI, BasePointer, DIB, -Offset);
600
601 // Replace uses of the alloca with the new location.
602 // Insert address calculation close to each use to work around PR27844.
603 std::string Name = std::string(AI->getName()) + ".unsafe";
604 while (!AI->use_empty()) {
605 Use &U = *AI->use_begin();
606 Instruction *User = cast<Instruction>(U.getUser());
607
608 Instruction *InsertBefore;
609 if (auto *PHI = dyn_cast<PHINode>(User))
610 InsertBefore = PHI->getIncomingBlock(U)->getTerminator();
611 else
612 InsertBefore = User;
613
614 IRBuilder<> IRBUser(InsertBefore);
615 Value *Off = IRBUser.CreateGEP(BasePointer, // BasePointer is i8*
616 ConstantInt::get(Int32Ty, -Offset));
617 Value *Replacement = IRBUser.CreateBitCast(Off, AI->getType(), Name);
618
619 if (auto *PHI = dyn_cast<PHINode>(User)) {
620 // PHI nodes may have multiple incoming edges from the same BB (why??),
621 // all must be updated at once with the same incoming value.
622 auto *BB = PHI->getIncomingBlock(U);
623 for (unsigned I = 0; I < PHI->getNumIncomingValues(); ++I)
624 if (PHI->getIncomingBlock(I) == BB)
625 PHI->setIncomingValue(I, Replacement);
626 } else {
627 U.set(Replacement);
628 }
629 }
630
631 AI->eraseFromParent();
632 }
633
634 // Re-align BasePointer so that our callees would see it aligned as
635 // expected.
636 // FIXME: no need to update BasePointer in leaf functions.
637 unsigned FrameSize = alignTo(SSL.getFrameSize(), StackAlignment);
638
639 // Update shadow stack pointer in the function epilogue.
640 IRB.SetInsertPoint(BasePointer->getNextNode());
641
642 Value *StaticTop =
643 IRB.CreateGEP(BasePointer, ConstantInt::get(Int32Ty, -FrameSize),
644 "unsafe_stack_static_top");
645 IRB.CreateStore(StaticTop, UnsafeStackPtr);
646 return StaticTop;
647}
648
649void SafeStack::moveDynamicAllocasToUnsafeStack(
650 Function &F, Value *UnsafeStackPtr, AllocaInst *DynamicTop,
651 ArrayRef<AllocaInst *> DynamicAllocas) {
652 DIBuilder DIB(*F.getParent());
653
654 for (AllocaInst *AI : DynamicAllocas) {
655 IRBuilder<> IRB(AI);
656
657 // Compute the new SP value (after AI).
658 Value *ArraySize = AI->getArraySize();
659 if (ArraySize->getType() != IntPtrTy)
660 ArraySize = IRB.CreateIntCast(ArraySize, IntPtrTy, false);
661
662 Type *Ty = AI->getAllocatedType();
663 uint64_t TySize = DL.getTypeAllocSize(Ty);
664 Value *Size = IRB.CreateMul(ArraySize, ConstantInt::get(IntPtrTy, TySize));
665
666 Value *SP = IRB.CreatePtrToInt(IRB.CreateLoad(UnsafeStackPtr), IntPtrTy);
667 SP = IRB.CreateSub(SP, Size);
668
669 // Align the SP value to satisfy the AllocaInst, type and stack alignments.
670 unsigned Align = std::max(
671 std::max((unsigned)DL.getPrefTypeAlignment(Ty), AI->getAlignment()),
672 (unsigned)StackAlignment);
673
674 assert(isPowerOf2_32(Align))((isPowerOf2_32(Align)) ? static_cast<void> (0) : __assert_fail
("isPowerOf2_32(Align)", "/build/llvm-toolchain-snapshot-8~svn345461/lib/CodeGen/SafeStack.cpp"
, 674, __PRETTY_FUNCTION__))
;
675 Value *NewTop = IRB.CreateIntToPtr(
676 IRB.CreateAnd(SP, ConstantInt::get(IntPtrTy, ~uint64_t(Align - 1))),
677 StackPtrTy);
678
679 // Save the stack pointer.
680 IRB.CreateStore(NewTop, UnsafeStackPtr);
681 if (DynamicTop)
682 IRB.CreateStore(NewTop, DynamicTop);
683
684 Value *NewAI = IRB.CreatePointerCast(NewTop, AI->getType());
685 if (AI->hasName() && isa<Instruction>(NewAI))
686 NewAI->takeName(AI);
687
688 replaceDbgDeclareForAlloca(AI, NewAI, DIB, DIExpression::NoDeref, 0,
689 DIExpression::NoDeref);
690 AI->replaceAllUsesWith(NewAI);
691 AI->eraseFromParent();
692 }
693
694 if (!DynamicAllocas.empty()) {
695 // Now go through the instructions again, replacing stacksave/stackrestore.
696 for (inst_iterator It = inst_begin(&F), Ie = inst_end(&F); It != Ie;) {
697 Instruction *I = &*(It++);
698 auto II = dyn_cast<IntrinsicInst>(I);
699 if (!II)
700 continue;
701
702 if (II->getIntrinsicID() == Intrinsic::stacksave) {
703 IRBuilder<> IRB(II);
704 Instruction *LI = IRB.CreateLoad(UnsafeStackPtr);
705 LI->takeName(II);
706 II->replaceAllUsesWith(LI);
707 II->eraseFromParent();
708 } else if (II->getIntrinsicID() == Intrinsic::stackrestore) {
709 IRBuilder<> IRB(II);
710 Instruction *SI = IRB.CreateStore(II->getArgOperand(0), UnsafeStackPtr);
711 SI->takeName(II);
712 assert(II->use_empty())((II->use_empty()) ? static_cast<void> (0) : __assert_fail
("II->use_empty()", "/build/llvm-toolchain-snapshot-8~svn345461/lib/CodeGen/SafeStack.cpp"
, 712, __PRETTY_FUNCTION__))
;
713 II->eraseFromParent();
714 }
715 }
716 }
717}
718
719bool SafeStack::ShouldInlinePointerAddress(CallSite &CS) {
720 Function *Callee = CS.getCalledFunction();
721 if (CS.hasFnAttr(Attribute::AlwaysInline) && isInlineViable(*Callee))
722 return true;
723 if (Callee->isInterposable() || Callee->hasFnAttribute(Attribute::NoInline) ||
724 CS.isNoInline())
725 return false;
726 return true;
727}
728
729void SafeStack::TryInlinePointerAddress() {
730 if (!isa<CallInst>(UnsafeStackPtr))
731 return;
732
733 if(F.hasFnAttribute(Attribute::OptimizeNone))
734 return;
735
736 CallSite CS(UnsafeStackPtr);
737 Function *Callee = CS.getCalledFunction();
738 if (!Callee || Callee->isDeclaration())
739 return;
740
741 if (!ShouldInlinePointerAddress(CS))
742 return;
743
744 InlineFunctionInfo IFI;
745 InlineFunction(CS, IFI);
746}
747
748bool SafeStack::run() {
749 assert(F.hasFnAttribute(Attribute::SafeStack) &&((F.hasFnAttribute(Attribute::SafeStack) && "Can't run SafeStack on a function without the attribute"
) ? static_cast<void> (0) : __assert_fail ("F.hasFnAttribute(Attribute::SafeStack) && \"Can't run SafeStack on a function without the attribute\""
, "/build/llvm-toolchain-snapshot-8~svn345461/lib/CodeGen/SafeStack.cpp"
, 750, __PRETTY_FUNCTION__))
750 "Can't run SafeStack on a function without the attribute")((F.hasFnAttribute(Attribute::SafeStack) && "Can't run SafeStack on a function without the attribute"
) ? static_cast<void> (0) : __assert_fail ("F.hasFnAttribute(Attribute::SafeStack) && \"Can't run SafeStack on a function without the attribute\""
, "/build/llvm-toolchain-snapshot-8~svn345461/lib/CodeGen/SafeStack.cpp"
, 750, __PRETTY_FUNCTION__))
;
751 assert(!F.isDeclaration() && "Can't run SafeStack on a function declaration")((!F.isDeclaration() && "Can't run SafeStack on a function declaration"
) ? static_cast<void> (0) : __assert_fail ("!F.isDeclaration() && \"Can't run SafeStack on a function declaration\""
, "/build/llvm-toolchain-snapshot-8~svn345461/lib/CodeGen/SafeStack.cpp"
, 751, __PRETTY_FUNCTION__))
;
752
753 ++NumFunctions;
754
755 SmallVector<AllocaInst *, 16> StaticAllocas;
756 SmallVector<AllocaInst *, 4> DynamicAllocas;
757 SmallVector<Argument *, 4> ByValArguments;
758 SmallVector<ReturnInst *, 4> Returns;
759
760 // Collect all points where stack gets unwound and needs to be restored
761 // This is only necessary because the runtime (setjmp and unwind code) is
762 // not aware of the unsafe stack and won't unwind/restore it properly.
763 // To work around this problem without changing the runtime, we insert
764 // instrumentation to restore the unsafe stack pointer when necessary.
765 SmallVector<Instruction *, 4> StackRestorePoints;
766
767 // Find all static and dynamic alloca instructions that must be moved to the
768 // unsafe stack, all return instructions and stack restore points.
769 findInsts(F, StaticAllocas, DynamicAllocas, ByValArguments, Returns,
770 StackRestorePoints);
771
772 if (StaticAllocas.empty() && DynamicAllocas.empty() &&
773 ByValArguments.empty() && StackRestorePoints.empty())
774 return false; // Nothing to do in this function.
775
776 if (!StaticAllocas.empty() || !DynamicAllocas.empty() ||
777 !ByValArguments.empty())
778 ++NumUnsafeStackFunctions; // This function has the unsafe stack.
779
780 if (!StackRestorePoints.empty())
781 ++NumUnsafeStackRestorePointsFunctions;
782
783 IRBuilder<> IRB(&F.front(), F.begin()->getFirstInsertionPt());
784 // Calls must always have a debug location, or else inlining breaks. So
785 // we explicitly set a artificial debug location here.
786 if (DISubprogram *SP = F.getSubprogram())
787 IRB.SetCurrentDebugLocation(DebugLoc::get(SP->getScopeLine(), 0, SP));
788 if (SafeStackUsePointerAddress) {
789 Value *Fn = F.getParent()->getOrInsertFunction(
790 "__safestack_pointer_address", StackPtrTy->getPointerTo(0));
791 UnsafeStackPtr = IRB.CreateCall(Fn);
792 } else {
793 UnsafeStackPtr = TL.getSafeStackPointerLocation(IRB);
794 }
795
796 // Load the current stack pointer (we'll also use it as a base pointer).
797 // FIXME: use a dedicated register for it ?
798 Instruction *BasePointer =
799 IRB.CreateLoad(UnsafeStackPtr, false, "unsafe_stack_ptr");
800 assert(BasePointer->getType() == StackPtrTy)((BasePointer->getType() == StackPtrTy) ? static_cast<void
> (0) : __assert_fail ("BasePointer->getType() == StackPtrTy"
, "/build/llvm-toolchain-snapshot-8~svn345461/lib/CodeGen/SafeStack.cpp"
, 800, __PRETTY_FUNCTION__))
;
801
802 AllocaInst *StackGuardSlot = nullptr;
803 // FIXME: implement weaker forms of stack protector.
804 if (F.hasFnAttribute(Attribute::StackProtect) ||
805 F.hasFnAttribute(Attribute::StackProtectStrong) ||
806 F.hasFnAttribute(Attribute::StackProtectReq)) {
807 Value *StackGuard = getStackGuard(IRB, F);
808 StackGuardSlot = IRB.CreateAlloca(StackPtrTy, nullptr);
809 IRB.CreateStore(StackGuard, StackGuardSlot);
810
811 for (ReturnInst *RI : Returns) {
812 IRBuilder<> IRBRet(RI);
813 checkStackGuard(IRBRet, F, *RI, StackGuardSlot, StackGuard);
814 }
815 }
816
817 // The top of the unsafe stack after all unsafe static allocas are
818 // allocated.
819 Value *StaticTop =
820 moveStaticAllocasToUnsafeStack(IRB, F, StaticAllocas, ByValArguments,
821 Returns, BasePointer, StackGuardSlot);
822
823 // Safe stack object that stores the current unsafe stack top. It is updated
824 // as unsafe dynamic (non-constant-sized) allocas are allocated and freed.
825 // This is only needed if we need to restore stack pointer after longjmp
826 // or exceptions, and we have dynamic allocations.
827 // FIXME: a better alternative might be to store the unsafe stack pointer
828 // before setjmp / invoke instructions.
829 AllocaInst *DynamicTop = createStackRestorePoints(
830 IRB, F, StackRestorePoints, StaticTop, !DynamicAllocas.empty());
831
832 // Handle dynamic allocas.
833 moveDynamicAllocasToUnsafeStack(F, UnsafeStackPtr, DynamicTop,
834 DynamicAllocas);
835
836 // Restore the unsafe stack pointer before each return.
837 for (ReturnInst *RI : Returns) {
838 IRB.SetInsertPoint(RI);
839 IRB.CreateStore(BasePointer, UnsafeStackPtr);
840 }
841
842 TryInlinePointerAddress();
843
844 LLVM_DEBUG(dbgs() << "[SafeStack] safestack applied\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] safestack applied\n"
; } } while (false)
;
845 return true;
846}
847
848class SafeStackLegacyPass : public FunctionPass {
849 const TargetMachine *TM = nullptr;
850
851public:
852 static char ID; // Pass identification, replacement for typeid..
853
854 SafeStackLegacyPass() : FunctionPass(ID) {
855 initializeSafeStackLegacyPassPass(*PassRegistry::getPassRegistry());
856 }
857
858 void getAnalysisUsage(AnalysisUsage &AU) const override {
859 AU.addRequired<TargetPassConfig>();
860 AU.addRequired<TargetLibraryInfoWrapperPass>();
861 AU.addRequired<AssumptionCacheTracker>();
862 }
863
864 bool runOnFunction(Function &F) override {
865 LLVM_DEBUG(dbgs() << "[SafeStack] Function: " << F.getName() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] Function: " <<
F.getName() << "\n"; } } while (false)
;
866
867 if (!F.hasFnAttribute(Attribute::SafeStack)) {
868 LLVM_DEBUG(dbgs() << "[SafeStack] safestack is not requested"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] safestack is not requested"
" for this function\n"; } } while (false)
869 " for this function\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] safestack is not requested"
" for this function\n"; } } while (false)
;
870 return false;
871 }
872
873 if (F.isDeclaration()) {
874 LLVM_DEBUG(dbgs() << "[SafeStack] function definition"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] function definition"
" is not available\n"; } } while (false)
875 " is not available\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("safe-stack")) { dbgs() << "[SafeStack] function definition"
" is not available\n"; } } while (false)
;
876 return false;
877 }
878
879 TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
880 auto *TL = TM->getSubtargetImpl(F)->getTargetLowering();
881 if (!TL)
882 report_fatal_error("TargetLowering instance is required");
883
884 auto *DL = &F.getParent()->getDataLayout();
885 auto &TLI = getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
886 auto &ACT = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
887
888 // Compute DT and LI only for functions that have the attribute.
889 // This is only useful because the legacy pass manager doesn't let us
890 // compute analyzes lazily.
891 // In the backend pipeline, nothing preserves DT before SafeStack, so we
892 // would otherwise always compute it wastefully, even if there is no
893 // function with the safestack attribute.
894 DominatorTree DT(F);
895 LoopInfo LI(DT);
896
897 ScalarEvolution SE(F, TLI, ACT, DT, LI);
898
899 return SafeStack(F, *TL, *DL, SE).run();
900 }
901};
902
903} // end anonymous namespace
904
905char SafeStackLegacyPass::ID = 0;
906
907INITIALIZE_PASS_BEGIN(SafeStackLegacyPass, DEBUG_TYPE,static void *initializeSafeStackLegacyPassPassOnce(PassRegistry
&Registry) {
908 "Safe Stack instrumentation pass", false, false)static void *initializeSafeStackLegacyPassPassOnce(PassRegistry
&Registry) {
909INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)initializeTargetPassConfigPass(Registry);
910INITIALIZE_PASS_END(SafeStackLegacyPass, DEBUG_TYPE,PassInfo *PI = new PassInfo( "Safe Stack instrumentation pass"
, "safe-stack", &SafeStackLegacyPass::ID, PassInfo::NormalCtor_t
(callDefaultCtor<SafeStackLegacyPass>), false, false); Registry
.registerPass(*PI, true); return PI; } static llvm::once_flag
InitializeSafeStackLegacyPassPassFlag; void llvm::initializeSafeStackLegacyPassPass
(PassRegistry &Registry) { llvm::call_once(InitializeSafeStackLegacyPassPassFlag
, initializeSafeStackLegacyPassPassOnce, std::ref(Registry));
}
911 "Safe Stack instrumentation pass", false, false)PassInfo *PI = new PassInfo( "Safe Stack instrumentation pass"
, "safe-stack", &SafeStackLegacyPass::ID, PassInfo::NormalCtor_t
(callDefaultCtor<SafeStackLegacyPass>), false, false); Registry
.registerPass(*PI, true); return PI; } static llvm::once_flag
InitializeSafeStackLegacyPassPassFlag; void llvm::initializeSafeStackLegacyPassPass
(PassRegistry &Registry) { llvm::call_once(InitializeSafeStackLegacyPassPassFlag
, initializeSafeStackLegacyPassPassOnce, std::ref(Registry));
}
912
913FunctionPass *llvm::createSafeStackPass() { return new SafeStackLegacyPass(); }