From: Anders Carlsson <andersca@mac.com>
Date: Sat, 16 Feb 2008 01:20:23 +0000 (+0000)
Subject: Make sizeof and __alignof work correctly with packed structs.
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=6a24acbb3dbb3bea9426716bee6ad6023ad15f3f;p=clang

Make sizeof and __alignof work correctly with packed structs.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@47202 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/AST/ASTContext.cpp b/AST/ASTContext.cpp
index 608858b55f..7d7decb6ff 100644
--- a/AST/ASTContext.cpp
+++ b/AST/ASTContext.cpp
@@ -319,10 +319,13 @@ const ASTRecordLayout &ASTContext::getASTRecordLayout(const RecordDecl *D,
   unsigned RecordAlign = 8;  // Default alignment = 1 byte = 8 bits.
 
   if (D->getKind() != Decl::Union) {
+    bool StructIsPacked = D->getAttr<PackedAttr>();
+    
     // Layout each field, for now, just sequentially, respecting alignment.  In
     // the future, this will need to be tweakable by targets.
     for (unsigned i = 0, e = D->getNumMembers(); i != e; ++i) {
       const FieldDecl *FD = D->getMember(i);
+      bool FieldIsPacked = StructIsPacked || FD->getAttr<PackedAttr>();
       uint64_t FieldSize;
       unsigned FieldAlign;
       if (FD->getType()->isIncompleteType()) {
@@ -331,12 +334,12 @@ const ASTRecordLayout &ASTContext::getASTRecordLayout(const RecordDecl *D,
         // Flexible array members don't have any size, but they
         // have to be aligned appropriately for their element type.
         const ArrayType* ATy = FD->getType()->getAsArrayType();
-        FieldAlign = getTypeAlign(ATy->getElementType(), L);
+        FieldAlign = FieldIsPacked ? 8 : getTypeAlign(ATy->getElementType(), L);
         FieldSize = 0;
       } else {
         std::pair<uint64_t, unsigned> FieldInfo = getTypeInfo(FD->getType(), L);
         FieldSize = FieldInfo.first;
-        FieldAlign = FieldInfo.second;
+        FieldAlign = FieldIsPacked ? 8 : FieldInfo.second;
       }
 
       // Round up the current record size to the field's alignment boundary.
diff --git a/AST/Expr.cpp b/AST/Expr.cpp
index b8c564e94e..0410e284a7 100644
--- a/AST/Expr.cpp
+++ b/AST/Expr.cpp
@@ -784,16 +784,18 @@ bool Expr::isIntegerConstantExpr(llvm::APSInt &Result, ASTContext &Ctx,
     if (Exp->getArgumentType()->isFunctionType()) {
       // GCC extension: sizeof(function) = 1.
       Result = Exp->isSizeOf() ? 1 : 4;
-    } else if (Exp->isSizeOf()) {
+    } else { 
       unsigned CharSize =
         Ctx.Target.getCharWidth(Ctx.getFullLoc(Exp->getOperatorLoc()));
       
-      Result = Ctx.getTypeSize(Exp->getArgumentType(),
-                               Exp->getOperatorLoc()) / CharSize;
+      if (Exp->isSizeOf())
+        Result = Ctx.getTypeSize(Exp->getArgumentType(),
+                                 Exp->getOperatorLoc()) / CharSize;
+      else
+        Result = Ctx.getTypeAlign(Exp->getArgumentType(), 
+                                  Exp->getOperatorLoc()) / CharSize;
     }
-    else
-      Result = Ctx.getTypeAlign(Exp->getArgumentType(), Exp->getOperatorLoc());
-    
+
     break;
   }
   case BinaryOperatorClass: {
diff --git a/include/clang/AST/Decl.h b/include/clang/AST/Decl.h
index bf8a214eb1..0bf737c1ea 100644
--- a/include/clang/AST/Decl.h
+++ b/include/clang/AST/Decl.h
@@ -138,9 +138,9 @@ public:
   void addAttr(Attr *attr);
   const Attr *getAttrs() const;
 
-  template<typename T> T *getAttr() {
-    for (Attr *attr = getAttrs(); attr; attr = attr->getNext())
-      if (T *V = dyn_cast<T>(attr))
+  template<typename T> const T *getAttr() const {
+    for (const Attr *attr = getAttrs(); attr; attr = attr->getNext())
+      if (const T *V = dyn_cast<T>(attr))
         return V;
 
     return 0;
diff --git a/test/Sema/struct-packed-align.c b/test/Sema/struct-packed-align.c
new file mode 100644
index 0000000000..23885a5461
--- /dev/null
+++ b/test/Sema/struct-packed-align.c
@@ -0,0 +1,37 @@
+// RUN: clang %s -fsyntax-only -verify
+
+struct s {
+    char a;
+    int b  __attribute__((packed));
+    char c;
+    int d;
+};
+
+struct __attribute__((packed)) packed_s {
+    char a;
+    int b  __attribute__((packed));
+    char c;
+    int d;
+};
+
+struct fas {
+    char a;
+    int b[];
+};
+
+struct __attribute__((packed)) packed_fas {
+    char a;
+    int b[];
+};
+
+extern int a1[sizeof(struct s) == 12 ? 1 : -1];
+extern int a2[__alignof(struct s) == 4 ? 1 : -1];
+
+extern int b1[sizeof(struct packed_s) == 10 ? 1 : -1];
+extern int b2[__alignof(struct packed_s) == 1 ? 1 : -1];
+
+extern int c1[sizeof(struct fas) == 4 ? 1 : -1];
+extern int c2[__alignof(struct fas) == 4 ? 1 : -1];
+
+extern int d1[sizeof(struct packed_fas) == 1 ? 1 : -1];
+extern int d2[__alignof(struct packed_fas) == 1 ? 1 : -1];