Unaligned Access Warning Added

Added warning for potential cases of
unaligned access when option
-mno-unaligned-access has been specified

clang/include/clang/Basic/DiagnosticASTKinds.td

@@ -590,4 +590,9 @@ def warn_padded_struct_size : Warning<
   InGroup<Padded>, DefaultIgnore;
 def warn_unnecessary_packed : Warning<
   "packed attribute is unnecessary for %0">, InGroup<Packed>, DefaultIgnore;
+
+// -Wunaligned-access
+def warn_unaligned_access : Warning<
+  "field %1 within its parent %0 has an alignment greater than its parent "
+  "this may be caused by %0 being packed and can lead to unaligned accesses">, InGroup<UnalignedAccess>, DefaultIgnore;
 }

clang/include/clang/Basic/DiagnosticGroups.td

@@ -542,6 +542,7 @@ def ExplicitInitializeCall : DiagGroup<"explicit-initialize-call">;
 def OrderedCompareFunctionPointers : DiagGroup<"ordered-compare-function-pointers">;
 def Packed : DiagGroup<"packed">;
 def Padded : DiagGroup<"padded">;
+def UnalignedAccess : DiagGroup<"unaligned-access">;
 
 def PessimizingMove : DiagGroup<"pessimizing-move">;
 def ReturnStdMove : DiagGroup<"return-std-move">;

clang/lib/AST/RecordLayoutBuilder.cpp

@@ -2021,6 +2021,7 @@ void ItaniumRecordLayoutBuilder::LayoutField(const FieldDecl *D,
   CharUnits UnpackedFieldAlign =
       !DefaultsToAIXPowerAlignment ? FieldAlign : PreferredAlign;
   CharUnits UnpackedFieldOffset = FieldOffset;
+  CharUnits OriginalFieldAlign = UnpackedFieldAlign;
 
   if (FieldPacked) {
     FieldAlign = CharUnits::One();
@@ -2105,6 +2106,22 @@ void ItaniumRecordLayoutBuilder::LayoutField(const FieldDecl *D,
   // Remember max struct/class ABI-specified alignment.
   UnadjustedAlignment = std::max(UnadjustedAlignment, FieldAlign);
   UpdateAlignment(FieldAlign, UnpackedFieldAlign, PreferredAlign);
+
+  // For checking the alignment of inner fields against
+  // the alignment of its parent record.
+  if (const RecordDecl *RD = D->getParent()) {
+    // Check if packed attribute or pragma pack is present.
+    if (RD->hasAttr<PackedAttr>() || !MaxFieldAlignment.isZero())
+      if (FieldAlign < OriginalFieldAlign)
+        if (D->getType()->isRecordType()) {
+          // If the offset is a multiple of the alignment of
+          // the type, raise the warning.
+          // TODO: Takes no account the alignment of the outer struct
+          if (FieldOffset % OriginalFieldAlign != 0)
+            Diag(D->getLocation(), diag::warn_unaligned_access)
+                << Context.getTypeDeclType(RD) << D->getName();
+        }
+  }
 }
 
 void ItaniumRecordLayoutBuilder::FinishLayout(const NamedDecl *D) {

clang/lib/Driver/ToolChains/Arch/AArch64.cpp

@@ -221,6 +221,7 @@ getAArch64MicroArchFeaturesFromMcpu(const Driver &D, StringRef Mcpu,
 void aarch64::getAArch64TargetFeatures(const Driver &D,
                                        const llvm::Triple &Triple,
                                        const ArgList &Args,
+                                       llvm::opt::ArgStringList &CmdArgs,
                                        std::vector<StringRef> &Features,
                                        bool ForAS) {
   Arg *A;
@@ -464,10 +465,14 @@ fp16_fml_fallthrough:
 
   if (Arg *A = Args.getLastArg(options::OPT_mno_unaligned_access,
                                options::OPT_munaligned_access)) {
-    if (A->getOption().matches(options::OPT_mno_unaligned_access))
+    if (A->getOption().matches(options::OPT_mno_unaligned_access)) {
       Features.push_back("+strict-align");
-  } else if (Triple.isOSOpenBSD())
+      CmdArgs.push_back("-Wunaligned-access");
+    }
+  } else if (Triple.isOSOpenBSD()) {
     Features.push_back("+strict-align");
+    CmdArgs.push_back("-Wunaligned-access");
+  }
 
   if (Args.hasArg(options::OPT_ffixed_x1))
     Features.push_back("+reserve-x1");

clang/lib/Driver/ToolChains/Arch/AArch64.h

@@ -22,6 +22,7 @@ namespace aarch64 {
 
 void getAArch64TargetFeatures(const Driver &D, const llvm::Triple &Triple,
                               const llvm::opt::ArgList &Args,
+                              llvm::opt::ArgStringList &CmdArgs,
                               std::vector<llvm::StringRef> &Features,
                               bool ForAS);
 

clang/lib/Driver/ToolChains/Arch/ARM.cpp

@@ -769,10 +769,11 @@ fp16_fml_fallthrough:
   }
 
   // Kernel code has more strict alignment requirements.
-  if (KernelOrKext)
+  if (KernelOrKext) {
     Features.push_back("+strict-align");
-  else if (Arg *A = Args.getLastArg(options::OPT_mno_unaligned_access,
-                                    options::OPT_munaligned_access)) {
+    CmdArgs.push_back("-Wunaligned-access");
+  } else if (Arg *A = Args.getLastArg(options::OPT_mno_unaligned_access,
+                                      options::OPT_munaligned_access)) {
     if (A->getOption().matches(options::OPT_munaligned_access)) {
       // No v6M core supports unaligned memory access (v6M ARM ARM A3.2).
       if (Triple.getSubArch() == llvm::Triple::SubArchType::ARMSubArch_v6m)
@@ -781,8 +782,10 @@ fp16_fml_fallthrough:
       // access either.
       else if (Triple.getSubArch() == llvm::Triple::SubArchType::ARMSubArch_v8m_baseline)
         D.Diag(diag::err_target_unsupported_unaligned) << "v8m.base";
-    } else
+    } else {
       Features.push_back("+strict-align");
+      CmdArgs.push_back("-Wunaligned-access");
+    }
   } else {
     // Assume pre-ARMv6 doesn't support unaligned accesses.
     //
@@ -801,14 +804,20 @@ fp16_fml_fallthrough:
     int VersionNum = getARMSubArchVersionNumber(Triple);
     if (Triple.isOSDarwin() || Triple.isOSNetBSD()) {
       if (VersionNum < 6 ||
-          Triple.getSubArch() == llvm::Triple::SubArchType::ARMSubArch_v6m)
+          Triple.getSubArch() == llvm::Triple::SubArchType::ARMSubArch_v6m) {
         Features.push_back("+strict-align");
+        CmdArgs.push_back("-Wunaligned-access");
+      }
     } else if (Triple.isOSLinux() || Triple.isOSNaCl() ||
                Triple.isOSWindows()) {
-      if (VersionNum < 7)
+      if (VersionNum < 7) {
         Features.push_back("+strict-align");
-    } else
+        CmdArgs.push_back("-Wunaligned-access");
+      }
+    } else {
       Features.push_back("+strict-align");
+      CmdArgs.push_back("-Wunaligned-access");
+    }
   }
 
   // llvm does not support reserving registers in general. There is support

clang/lib/Driver/ToolChains/Clang.cpp

@@ -346,7 +346,8 @@ static void getTargetFeatures(const Driver &D, const llvm::Triple &Triple,
   case llvm::Triple::aarch64:
   case llvm::Triple::aarch64_32:
   case llvm::Triple::aarch64_be:
-    aarch64::getAArch64TargetFeatures(D, Triple, Args, Features, ForAS);
+    aarch64::getAArch64TargetFeatures(D, Triple, Args, CmdArgs, Features,
+                                      ForAS);
     break;
   case llvm::Triple::x86:
   case llvm::Triple::x86_64:

clang/test/Sema/test-wunaligned-access.c

@@ -0,0 +1,476 @@
+// RUN: %clang_cc1 %s -verify -fsyntax-only -Wunaligned-access
+// expected-no-diagnostics
+// Set 1
+struct T1 {
+  char a;
+  int b;
+};
+
+struct __attribute__((packed)) U1 {
+  char a;
+  struct T1 b;
+  int c;
+};
+
+struct __attribute__((packed)) U2 {
+  char a;
+  struct T1 b __attribute__((aligned(2)));
+  int c;
+};
+
+struct __attribute__((packed)) U3 {
+  char a;
+  struct T1 b __attribute__((aligned(4)));
+  int c;
+};
+
+struct __attribute__((aligned(2))) U4 {
+  char a;
+  struct T1 b;
+  int c;
+};
+
+struct U5 {
+  char a;
+  struct T1 b;
+  int c;
+};
+
+struct U6 {
+  char a;
+  int b;
+  struct T1 c __attribute__((aligned(2)));
+};
+
+struct __attribute__((packed)) U7 {
+  short a;
+  short b;
+  char c;
+  struct T1 d;
+};
+
+struct U8 {
+  short a;
+  short b;
+  char c;
+  struct T1 d;
+};
+
+struct __attribute__((packed)) U9 {
+  short a;
+  short b;
+  char c;
+  struct T1 d __attribute__((aligned(4)));
+};
+
+struct __attribute__((packed)) U10 {
+  short a;
+  short b;
+  char c;
+  struct T1 d __attribute__((aligned(2)));
+};
+
+struct __attribute__((aligned(2))) U11 {
+  short a;
+  short b;
+  char c;
+  struct T1 d;
+};
+
+// Set 2
+#pragma pack(push, 1)
+
+struct U12 {
+  char a;
+  struct T1 b;
+  int c;
+};
+
+struct __attribute__((packed)) U13 {
+  char a;
+  struct T1 b;
+  int c;
+};
+
+struct __attribute__((packed)) U14 {
+  char a;
+  struct T1 b __attribute__((aligned(4)));
+  int c;
+};
+
+struct __attribute__((aligned(2))) U15 {
+  char a;
+  struct T1 b;
+  int c;
+};
+
+struct U16 {
+  char a;
+  char b;
+  short c;
+  struct T1 d;
+};
+
+struct U17 {
+  char a;
+  char b;
+  short c;
+  struct T1 d __attribute__((aligned(4)));
+};
+
+struct __attribute__((packed)) U18 {
+  char a;
+  short b;
+  struct T1 c __attribute__((aligned(4)));
+};
+
+struct __attribute__((aligned(4))) U19 {
+  char a;
+  struct T1 b;
+  int c;
+};
+
+struct __attribute__((aligned(4))) U20 {
+  char a[4];
+  struct T1 b;
+  int c;
+};
+
+struct U21 {
+  char a;
+  short c;
+  struct T1 d;
+};
+
+struct U22 {
+  char a;
+  short c;
+  struct T1 d __attribute__((aligned(4)));
+};
+
+#pragma pack(pop)
+
+// Set 3
+
+struct __attribute__((packed)) U23 {
+  char a;
+  struct T1 b;
+  int c;
+};
+
+struct U24 {
+  char a;
+  struct T1 b;
+  int c;
+};
+
+struct U25 {
+  char a;
+  char b;
+  short c;
+  struct T1 d;
+};
+
+#pragma pack(push, 1)
+
+struct U26 {
+  char a;
+  char b;
+  short c;
+  struct T1 d;
+};
+
+#pragma pack(pop)
+
+// Set 4
+
+struct __attribute__((packed)) T2 {
+  char a;
+  struct T1 b;
+};
+
+struct T3 {
+  char a;
+  struct T1 b;
+};
+
+struct __attribute__((packed)) U27 {
+  char a;
+  struct T2 b;
+  int c;
+};
+
+struct U28 {
+  char a;
+  char _p[2];
+  struct T2 b;
+  int c;
+};
+
+struct U29 {
+  char a;
+  struct T3 b;
+  int c;
+};
+
+struct __attribute__((packed)) U30 {
+  char a;
+  struct T3 b;
+  int c;
+};
+
+struct __attribute__((packed)) U31 {
+  char a;
+  struct T2 b __attribute__((aligned(4)));
+};
+
+struct __attribute__((packed)) U32 {
+  char a;
+  char b;
+  char c;
+  char d;
+  struct T3 e;
+};
+
+struct __attribute__((packed)) U33 {
+  char a;
+  char b;
+  char c;
+  char d;
+  struct T2 e __attribute__((aligned(4)));
+};
+
+struct __attribute__((packed)) U34 {
+  char a;
+  struct T1 b __attribute__((packed));
+  struct T2 c;
+};
+
+struct __attribute__((packed)) U35 {
+  char a;
+  struct T4 {
+    char b;
+    struct T1 c;
+  } d;
+};
+
+// Set 5
+
+#pragma pack(push, 1)
+struct T5 {
+  char a;
+  struct T1 b;
+};
+#pragma pack(pop)
+
+#pragma pack(push, 1)
+struct U36 {
+  char a;
+  struct T5 b;
+  int c;
+};
+
+struct U37 {
+  char a;
+  struct T3 b;
+  int c;
+};
+#pragma pack(pop)
+struct U38 {
+  char a;
+  struct T5 b __attribute__((aligned(4)));
+  int c;
+};
+
+struct U39 {
+  char a;
+#pragma pack(push, 4)
+  struct T5 b;
+#pragma pack(pop)
+  int c;
+};
+
+// Set 6
+
+struct __attribute__((packed)) A1 {
+  char a;
+  struct T1 b;
+};
+
+struct A2 {
+  char a;
+  struct T1 b;
+};
+
+struct __attribute__((packed)) A3 {
+  char a;
+  struct T1 b __attribute__((aligned(4)));
+};
+
+#pragma pack(push, 1)
+struct A4 {
+  char a;
+  struct T1 b;
+};
+
+struct A5 {
+  char a;
+  struct T1 b __attribute__((aligned(4)));
+};
+#pragma pack(pop)
+
+struct __attribute__((packed)) A6 {
+  struct T1 a;
+};
+
+struct A7 {
+  char a;
+  struct T1 b __attribute__((packed));
+};
+
+struct A8 {
+  char a;
+  char b;
+  short c;
+  struct T1 d;
+};
+
+struct A9 {
+  char a;
+  struct T2 b;
+};
+
+struct A10 {
+  char a;
+  struct T2 b __attribute__((aligned(4)));
+};
+
+struct __attribute__((packed)) A11 {
+  char a;
+  struct T2 b;
+};
+
+struct __attribute__((packed)) U40 {
+  char a;
+  struct A1 b;
+  int c;
+};
+
+struct __attribute__((packed)) U41 {
+  char a;
+  struct A3 b;
+  int c;
+};
+
+#pragma pack(push, 1)
+struct U42 {
+  char a;
+  struct A1 b;
+  int c;
+};
+#pragma pack(pop)
+
+struct __attribute__((packed)) U43 {
+  char a;
+  struct A9 b;
+  int c;
+};
+
+struct __attribute__((packed)) U44 {
+  char a;
+  struct A10 b;
+  int c;
+};
+
+#pragma pack(push, 1)
+
+struct U45 {
+  char a;
+  struct A10 b;
+  int c;
+};
+
+#pragma pack(pop)
+
+struct __attribute__((packed)) U46 {
+  char a;
+  struct A2 b;
+  int c;
+};
+
+struct __attribute__((packed)) U47 {
+  char a;
+  struct A8 b;
+  int c;
+};
+
+#pragma pack(push, 1)
+struct U48 {
+  char a;
+  struct A8 b;
+  int c;
+};
+#pragma pack(pop)
+
+struct U49 {
+  char a;
+  struct A11 b;
+  int c;
+};
+
+struct U50 {
+  char a;
+  struct A1 b;
+  int c;
+};
+
+struct U1 s1;
+struct U2 s2;
+struct U3 s3;
+struct U4 s4;
+struct U5 s5;
+struct U6 s6;
+struct U7 s7;
+struct U8 s8;
+struct U9 s9;
+struct U10 s10;
+struct U11 s11;
+struct U12 s12;
+struct U13 s13;
+struct U14 s14;
+struct U15 s15;
+struct U16 s16;
+struct U17 s17;
+struct U18 s18;
+struct U19 s19;
+struct U20 s20;
+struct U21 s21;
+struct U22 s22;
+struct U23 s23;
+struct U24 s24;
+struct U25 s25;
+struct U26 s26;
+struct U27 s27;
+struct U28 s28;
+struct U29 s29;
+struct U30 s30;
+struct U31 s31;
+struct U32 s32;
+struct U33 s33;
+struct U34 s34;
+struct U35 s35;
+struct U36 s36;
+struct U37 s37;
+struct U38 s38;
+struct U39 s39;
+struct U40 s40;
+struct U41 s41;
+struct U42 s42;
+struct U43 s43;
+struct U44 s44;
+struct U45 s45;
+struct U46 s46;
+struct U47 s47;
+struct U48 s48;
+struct U49 s49;
+struct U50 s50;

clang/test/Sema/test-wunaligned-access.cpp

@@ -0,0 +1,285 @@
+// RUN: %clang_cc1 %s -verify -fsyntax-only -Wunaligned-access
+
+// Packed-Unpacked Tests (No Pragma)
+
+struct T1 {
+  char a;
+  int b;
+};
+
+struct __attribute__((packed)) U1 // Causes warning
+{
+  char a;
+  T1 b; // expected-warning {{field b within its parent 'U1' has an alignment greater than its parent this may be caused by 'U1' being packed and can lead to unaligned accesses}}
+  int c;
+};
+
+struct __attribute__((packed)) U2 // No warning
+{
+  char a;
+  T1 b __attribute__((aligned(4)));
+  int c;
+};
+
+struct __attribute__((packed)) U3 // No warning
+{
+  char a;
+  char b;
+  short c;
+  T1 d;
+};
+
+struct __attribute__((packed)) U4 // No warning
+{
+  T1 a;
+  int b;
+};
+
+struct __attribute__((aligned(4), packed)) U5 // Causes warning
+{
+  char a;
+  T1 b; // expected-warning {{field b within its parent 'U5' has an alignment greater than its parent this may be caused by 'U5' being packed and can lead to unaligned accesses}}
+  int c;
+};
+
+struct __attribute__((aligned(4), packed)) U6 // No warning
+{
+  char a;
+  char b;
+  short c;
+  T1 d;
+};
+
+// Packed-Unpacked Tests with Pragma
+
+#pragma pack(push, 1)
+
+struct __attribute__((packed)) U7 // Causes warning
+{
+  char a;
+  T1 b; // expected-warning {{field b within its parent 'U7' has an alignment greater than its parent this may be caused by 'U7' being packed and can lead to unaligned accesses}}
+  int c;
+};
+
+struct __attribute__((packed)) U8 {
+  char a;
+  T1 b __attribute__((aligned(4))); // expected-warning {{field b within its parent 'U8' has an alignment greater than its parent this may be caused by 'U8' being packed and can lead to unaligned accesses}}
+  int c;
+};
+
+struct __attribute__((aligned(4))) U9 {
+  char a;
+  T1 b; // expected-warning {{field b within its parent 'U9' has an alignment greater than its parent this may be caused by 'U9' being packed and can lead to unaligned accesses}}
+  int c;
+};
+
+struct U10 {
+  char a;
+  T1 b; // expected-warning {{field b within its parent 'U10' has an alignment greater than its parent this may be caused by 'U10' being packed and can lead to unaligned accesses}}
+  int c;
+};
+
+#pragma pack(pop)
+
+// Packed-Packed Tests
+
+struct __attribute__((packed)) T2 {
+  char a;
+  int b;
+};
+
+struct __attribute__((packed)) U11 {
+  char a;
+  T2 b;
+  int c;
+};
+
+#pragma pack(push, 1)
+struct U12 // No warning
+{
+  char a;
+  T2 b;
+  int c;
+};
+#pragma pack(pop)
+
+// Unpacked-Packed Tests
+
+struct U13 // No warning
+{
+  char a;
+  T2 b;
+  int c;
+};
+
+struct U14 // No warning
+{
+  char a;
+  T2 b __attribute__((aligned(4)));
+  int c;
+};
+
+// Unpacked-Unpacked Test
+
+struct T3 {
+  char a;
+  int b;
+};
+
+struct U15 // No warning
+{
+  char a;
+  T3 b;
+  int c;
+};
+
+// Packed-Packed-Unpacked Test (No pragma)
+
+struct __attribute__((packed)) A1 {
+  char a;
+  T1 b; // expected-warning {{field b within its parent 'A1' has an alignment greater than its parent this may be caused by 'A1' being packed and can lead to unaligned accesses}}
+};
+
+struct __attribute__((packed)) U16 // No warning
+{
+  char a;
+  A1 b;
+  int c;
+};
+
+struct __attribute__((packed)) A2 // No warning
+{
+  char a;
+  T1 b __attribute__((aligned(4)));
+};
+
+struct __attribute__((packed)) U17 // Caused warning
+{
+  char a;
+  A2 b; // expected-warning {{field b within its parent 'U17' has an alignment greater than its parent this may be caused by 'U17' being packed and can lead to unaligned accesses}}
+  int c;
+};
+
+// Packed-Unpacked-Packed tests
+
+struct A3 {
+  char a;
+  T2 b;
+};
+
+struct __attribute__((packed)) U18 {
+  char a;
+  A3 b;
+  int c;
+};
+
+struct A4 {
+  char a;
+  T2 b;
+  int c;
+};
+
+#pragma pack(push, 1)
+struct U19 // Caused warning
+{
+  char a;
+  A4 b; // expected-warning {{field b within its parent 'U19' has an alignment greater than its parent this may be caused by 'U19' being packed and can lead to unaligned accesses}}
+  int c;
+};
+#pragma pack(pop)
+
+// Packed-Unpacked-Unpacked tests
+
+struct A5 {
+  char a;
+  T1 b;
+};
+
+struct __attribute__((packed)) U20 // Caused warning
+{
+  char a;
+  A5 b; // expected-warning {{field b within its parent 'U20' has an alignment greater than its parent this may be caused by 'U20' being packed and can lead to unaligned accesses}}
+  int c;
+};
+
+struct A6 {
+  char a;
+  T1 b;
+};
+
+#pragma pack(push, 1)
+struct U21 // Caused warning
+{
+  char a;
+  A6 b; // expected-warning {{field b within its parent 'U21' has an alignment greater than its parent this may be caused by 'U21' being packed and can lead to unaligned accesses}}
+  int c;
+};
+#pragma pack(pop)
+
+// Unpacked-Packed-Packed test
+
+struct __attribute__((packed)) A7 // No warning
+{
+  char a;
+  T2 b;
+};
+
+struct U22 // No warning
+{
+  char a;
+  A7 b;
+  int c;
+};
+
+// Unpacked-Packed-Unpacked tests
+
+struct __attribute__((packed)) A8 // Should cause warning
+{
+  char a;
+  T1 b; // expected-warning {{field b within its parent 'A8' has an alignment greater than its parent this may be caused by 'A8' being packed and can lead to unaligned accesses}}
+};
+
+struct U23 // No warning
+{
+  char a;
+  A8 b;
+  int c;
+};
+
+struct __attribute__((packed)) A9 // No warning
+{
+  char a;
+  T1 b __attribute__((aligned(4)));
+};
+
+struct U24 // No warning
+{
+  char a;
+  A9 b;
+  int c;
+};
+
+struct U1 s1;
+struct U2 s2;
+struct U3 s3;
+struct U4 s4;
+struct U5 s5;
+struct U6 s6;
+struct U7 s7;
+struct U8 s8;
+struct U9 s9;
+struct U10 s10;
+struct U11 s11;
+struct U12 s12;
+struct U13 s13;
+struct U14 s14;
+struct U15 s15;
+struct U16 s16;
+struct U17 s17;
+struct U18 s18;
+struct U19 s19;
+struct U20 s20;
+struct U21 s21;
+struct U22 s22;
+struct U23 s23;
+struct U24 s24;