[PATCH] D93072: Fix PR35902: incorrect alignment used for ubsan check.

[James Y Knight via Phabricator via cfe-commits]

jyknight created this revision.
jyknight added reviewers: rsmith, rnk.
jyknight requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

UBSan was using the complete-object align rather than nv alignment
when checking the "this" pointer of a method.

Furthermore, CGF.CXXABIThisAlignment was also being set incorrectly,
due to an incorrectly negated test. The latter doesn't appear to have
had any impact, due to it not really being used anywhere.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D93072

Files:
  clang/lib/CodeGen/CGCXXABI.cpp
  clang/lib/CodeGen/CodeGenFunction.cpp
  clang/test/CodeGenCXX/catch-undef-behavior.cpp


Index: clang/test/CodeGenCXX/catch-undef-behavior.cpp
===================================================================
--- clang/test/CodeGenCXX/catch-undef-behavior.cpp
+++ clang/test/CodeGenCXX/catch-undef-behavior.cpp
@@ -430,8 +430,8 @@
   // Note: C is laid out such that offsetof(C, B) + sizeof(B) extends outside
   // the C object.
   struct alignas(16) A { void *a1, *a2; };
-  struct B : virtual A { void *b; };
-  struct C : virtual A, virtual B {};
+  struct B : virtual A { void *b; void* g(); };
+  struct C : virtual A, virtual B { };
   // CHECK-LABEL: define {{.*}} @_ZN15VBaseObjectSize1fERNS_1BE(
   B &f(B &b) {
     // Size check: check for nvsize(B) == 16 (do not require size(B) == 32)
@@ -443,6 +443,15 @@
     // CHECK: and i64 [[PTRTOINT]], 7,
     return b;
   }
+
+  // CHECK-LABEL: define {{.*}} @_ZN15VBaseObjectSize1B1gEv(
+  void *B::g() {
+    // Ensure that the check on the "this" pointer also uses the proper
+    // alignment. We should be using nvalign(B) == 8, not 16.
+    // CHECK: [[PTRTOINT:%.+]] = ptrtoint {{.*}} to i64,
+    // CHECK: and i64 [[PTRTOINT]], 7
+    return nullptr;
+  }
 }
 
 namespace FunctionSanitizerVirtualCalls {
Index: clang/lib/CodeGen/CodeGenFunction.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenFunction.cpp
+++ clang/lib/CodeGen/CodeGenFunction.cpp
@@ -1137,11 +1137,9 @@
           MD->getParent()->getLambdaCaptureDefault() == LCD_None)
         SkippedChecks.set(SanitizerKind::Null, true);
 
-      EmitTypeCheck(isa<CXXConstructorDecl>(MD) ? TCK_ConstructorCall
-                                                : TCK_MemberCall,
-                    Loc, CXXABIThisValue, ThisTy,
-                    getContext().getTypeAlignInChars(ThisTy->getPointeeType()),
-                    SkippedChecks);
+      EmitTypeCheck(
+          isa<CXXConstructorDecl>(MD) ? TCK_ConstructorCall : TCK_MemberCall,
+          Loc, CXXABIThisValue, ThisTy, CXXABIThisAlignment, SkippedChecks);
     }
   }
 
Index: clang/lib/CodeGen/CGCXXABI.cpp
===================================================================
--- clang/lib/CodeGen/CGCXXABI.cpp
+++ clang/lib/CodeGen/CGCXXABI.cpp
@@ -136,7 +136,7 @@
   auto &Layout = CGF.getContext().getASTRecordLayout(MD->getParent());
   if (MD->getParent()->getNumVBases() == 0 || // avoid vcall in common case
       MD->getParent()->hasAttr<FinalAttr>() ||
-      !isThisCompleteObject(CGF.CurGD)) {
+      isThisCompleteObject(CGF.CurGD)) {
     CGF.CXXABIThisAlignment = Layout.getAlignment();
   } else {
     CGF.CXXABIThisAlignment = Layout.getNonVirtualAlignment();


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