[PEI] Don't re-allocate a pre-allocated stack protector slot

The LocalStackSlotPass pre-allocates a stack protector and makes sure
that it comes before the local variables on the stack.

We need to make sure that later during PEI we don't re-allocate a new
stack protector slot. If that happens, the new stack protector slot will
end up being **after** the local variables that it should be protecting.

Therefore, we would have two slots assigned for two different stack
protectors, one at the top of the stack, and one at the bottom. Since
PEI will overwrite the assigned slot for the stack protector, the load
that is used to compare the value of the stack protector will use the
slot assigned by PEI, which is wrong.

For this, we need to check if the object is pre-allocated, and re-use
that pre-allocated slot.

Differential Revision: https://reviews.llvm.org/D64757

llvm-svn: 366371

llvm/lib/CodeGen/LocalStackSlotAllocation.cpp

@@ -201,6 +201,14 @@ void LocalStackSlotPass::calculateFrameObjectOffsets(MachineFunction &Fn) {
   SmallSet<int, 16> ProtectedObjs;
   if (MFI.hasStackProtectorIndex()) {
     int StackProtectorFI = MFI.getStackProtectorIndex();
+
+    // We need to make sure we didn't pre-allocate the stack protector when
+    // doing this.
+    // If we already have a stack protector, this will re-assign it to a slot
+    // that is **not** covering the protected objects.
+    assert(!MFI.isObjectPreAllocated(StackProtectorFI) &&
+           "Stack protector pre-allocated in LocalStackSlotAllocation");
+
     StackObjSet LargeArrayObjs;
     StackObjSet SmallArrayObjs;
     StackObjSet AddrOfObjs;

llvm/lib/CodeGen/PrologEpilogInserter.cpp

@@ -933,8 +933,16 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &MF) {
     StackObjSet SmallArrayObjs;
     StackObjSet AddrOfObjs;
 
-    AdjustStackOffset(MFI, StackProtectorFI, StackGrowsDown, Offset, MaxAlign,
-                      Skew);
+    // If we need a stack protector, we need to make sure that
+    // LocalStackSlotPass didn't already allocate a slot for it.
+    // If we are told to use the LocalStackAllocationBlock, the stack protector
+    // is expected to be already pre-allocated.
+    if (!MFI.getUseLocalStackAllocationBlock())
+      AdjustStackOffset(MFI, StackProtectorFI, StackGrowsDown, Offset, MaxAlign,
+                        Skew);
+    else if (!MFI.isObjectPreAllocated(MFI.getStackProtectorIndex()))
+      llvm_unreachable(
+          "Stack protector not pre-allocated by LocalStackSlotPass.");
 
     // Assign large stack objects first.
     for (unsigned i = 0, e = MFI.getObjectIndexEnd(); i != e; ++i) {
@@ -968,6 +976,15 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &MF) {
       llvm_unreachable("Unexpected SSPLayoutKind.");
     }
 
+    // We expect **all** the protected stack objects to be pre-allocated by
+    // LocalStackSlotPass. If it turns out that PEI still has to allocate some
+    // of them, we may end up messing up the expected order of the objects.
+    if (MFI.getUseLocalStackAllocationBlock() &&
+        !(LargeArrayObjs.empty() && SmallArrayObjs.empty() &&
+          AddrOfObjs.empty()))
+      llvm_unreachable("Found protected stack objects not pre-allocated by "
+                       "LocalStackSlotPass.");
+
     AssignProtectedObjSet(LargeArrayObjs, ProtectedObjs, MFI, StackGrowsDown,
                           Offset, MaxAlign, Skew);
     AssignProtectedObjSet(SmallArrayObjs, ProtectedObjs, MFI, StackGrowsDown,

llvm/test/CodeGen/AArch64/stack-guard-reassign.ll

@@ -3,7 +3,7 @@
 ; Verify that the offset assigned to the stack protector is at the top of the
 ; frame, covering the locals.
 ; CHECK-LABEL: fn:
-; CHECK:      add x8, sp, #24
+; CHECK:      sub x8, x29, #24
 ; CHECK-NEXT: adrp x9, __stack_chk_guard
 ; CHECK-NEXT: ldr x9, [x9, :lo12:__stack_chk_guard]
 ; CHECK-NEXT: str x9, [x8]

llvm/test/CodeGen/AArch64/stack-guard-reassign.mir

@@ -11,13 +11,13 @@
 name:            main
 tracksRegLiveness: true
 frameInfo:
-# CHECK: stackSize: 560
+# CHECK: stackSize: 544
   stackProtector:  '%stack.0.StackGuardSlot'
 stack:
   - { id: 0, name: StackGuardSlot, size: 8, alignment: 8, stack-id: default }
 # Verify that the offset assigned to the stack protector is at the top of the
 # frame, covering the locals.
-# CHECK:       - { id: 0, name: StackGuardSlot, type: default, offset: -552, size: 8,
+# CHECK:       - { id: 0, name: StackGuardSlot, type: default, offset: -24, size: 8,
 # CHECK-NEXT:      alignment: 8, stack-id: default, callee-saved-register: '', callee-saved-restored: true,
 # CHECK-NEXT:      local-offset: -8, debug-info-variable: '', debug-info-expression: '',
 # CHECK-NEXT:      debug-info-location: '' }

llvm/test/CodeGen/AArch64/stack-guard-vaarg.ll

@@ -9,7 +9,7 @@
 ; CHECK: ldr [[GUARD:x[0-9]+]]{{.*}}:lo12:__stack_chk_guard]
 ; Make sure the canary is placed relative to the frame pointer, not
 ; the stack pointer.
-; CHECK: str [[GUARD]], [sp, #8]
+; CHECK: stur [[GUARD]], [x29, #-24]
 define void @test(i8* %i, ...) #0 {
 entry:
   %buf = alloca [10 x i8], align 1

llvm/test/CodeGen/ARM/stack-guard-reassign.ll

@@ -3,12 +3,12 @@
 ; Verify that the offset assigned to the stack protector is at the top of the
 ; frame, covering the locals.
 ; CHECK-LABEL: fn:
-; CHECK:      sub sp, sp, #40
+; CHECK:      sub sp, sp, #32
 ; CHECK-NEXT: sub sp, sp, #65536
-; CHECK-NEXT: add r1, sp, #28
+; CHECK-NEXT: add lr, sp, #65536
+; CHECK-NEXT: add r1, lr, #28
 ; CHECK-NEXT: ldr r2, .LCPI0_0
 ; CHECK-NEXT: ldr r3, [r2]
 ; CHECK-NEXT: str r3, [r1]
-; CHECK-NEXT: str r0, [sp, #32]
 ; CHECK: .LCPI0_0:
 ; CHECK-NEXT: .long __stack_chk_guard

llvm/test/CodeGen/PowerPC/stack-guard-reassign.ll

@@ -9,7 +9,9 @@
 ; CHECK-NEXT: ori 0, 0, 65488
 ; CHECK-NEXT: stwux 1, 1, 0
 ; CHECK-NEXT: subf 0, 0, 1
-; CHECK-NEXT: addi 4, 1, 36
+; CHECK-NEXT: lis 4, 1
+; CHECK-NEXT: ori 4, 4, 44
+; CHECK-NEXT: add 4, 1, 4
 ; CHECK-NEXT: lis 5, __stack_chk_guard@ha
 ; CHECK-NEXT: lwz 6, __stack_chk_guard@l(5)
 ; CHECK-NEXT: stw 6, 0(4)