C/C++: Add -Waddress-of-packed-member

diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index 6cf7614f682..2e09a36061f 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -1270,6 +1270,7 @@  extern void c_do_switch_warnings (splay_tree, location_t, tree, tree, bool,
 				  bool);
 extern void warn_for_omitted_condop (location_t, tree);
 extern bool warn_for_restrict (unsigned, tree *, unsigned);
+extern void warn_for_address_of_packed_member (tree, tree);
 
 /* Places where an lvalue, or modifiable lvalue, may be required.
    Used to select diagnostic messages in lvalue_error and
diff --git a/gcc/c-family/c-warn.c b/gcc/c-family/c-warn.c
index d0d9c7894a8..43805b2f6df 100644
--- a/gcc/c-family/c-warn.c
+++ b/gcc/c-family/c-warn.c
@@ -2587,3 +2587,120 @@  warn_for_multistatement_macros (location_t body_loc, location_t next_loc,
     inform (guard_loc, "some parts of macro expansion are not guarded by "
 	    "this %qs clause", guard_tinfo_to_string (keyword));
 }
+
+/* Return struct or union type if the right hand value, RHS, takes the
+   unaligned address of packed member of struct or union when assigning
+   to TYPE.  Otherwise, return NULL_TREE.  */
+
+static tree
+check_address_of_packed_member (tree type, tree rhs)
+{
+  tree base;
+  tree object;
+  tree field;
+
+  if (INDIRECT_REF_P (rhs))
+    rhs = TREE_OPERAND (rhs, 0);
+
+  switch (TREE_CODE (rhs))
+    {
+    case ADDR_EXPR:
+      base = TREE_OPERAND (rhs, 0);
+      while (TREE_CODE (base) == ARRAY_REF)
+	base = TREE_OPERAND (base, 0);
+      if (TREE_CODE (base) != COMPONENT_REF)
+	return NULL_TREE;
+      object = TREE_OPERAND (base, 0);
+      field = TREE_OPERAND (base, 1);
+      break;
+    case COMPONENT_REF:
+      object = TREE_OPERAND (rhs, 0);
+      field = TREE_OPERAND (rhs, 1);
+      break;
+    default:
+      return NULL_TREE;
+    }
+
+  tree context;
+  unsigned int type_align, record_align;
+
+  /* Check alignment of the data member.  */
+  if (TREE_CODE (field) == FIELD_DECL && DECL_PACKED (field))
+    {
+      /* Check the expected alignment against the field alignment.  */
+      type_align = TYPE_ALIGN (type);
+      context = DECL_CONTEXT (field);
+      record_align = TYPE_ALIGN (context);
+      if ((record_align % type_align) != 0)
+	return context;
+      tree field_off = byte_position (field);
+      if (!multiple_of_p (TREE_TYPE (field_off), field_off,
+			  size_int (type_align / BITS_PER_UNIT)))
+	return context;
+    }
+
+  /* Check alignment of the object.  */
+  if (TREE_CODE (object) == COMPONENT_REF)
+    {
+      field = TREE_OPERAND (object, 1);
+      if (TREE_CODE (field) == FIELD_DECL && DECL_PACKED (field))
+	{
+	  type_align = TYPE_ALIGN (type);
+	  context = DECL_CONTEXT (field);
+	  record_align = TYPE_ALIGN (context);
+	  if ((record_align % type_align) != 0)
+	    return context;
+	}
+    }
+
+  return NULL_TREE;
+}
+
+/* Warn if the right hand value, RHS, takes the unaligned address of
+   packed member of struct or union when assigning to TYPE.  Otherwise,
+   return NULL_TREE.  */
+
+void
+warn_for_address_of_packed_member (tree type, tree rhs)
+{
+  if (!warn_address_of_packed_member)
+    return;
+
+  /* Don't warn if we don't assign RHS to a pointer.  */
+  if (!POINTER_TYPE_P (type))
+    return;
+
+  /* Get the type of the pointer pointing to.  */
+  type = TREE_TYPE (type);
+
+  if (TREE_CODE (rhs) == NOP_EXPR)
+    rhs = TREE_OPERAND (rhs, 0);
+
+  tree context;
+
+  if (TREE_CODE (rhs) == COND_EXPR)
+    {
+      /* Check the THEN path first.  */
+      tree op1 = TREE_OPERAND (rhs, 1);
+      context = check_address_of_packed_member (type, op1);
+      if (context)
+	rhs = op1;
+      else
+	{
+	  /* Check the ELSE path.  */
+	  rhs = TREE_OPERAND (rhs, 2);
+	  context = check_address_of_packed_member (type, rhs);
+	}
+    }
+  else
+    context = check_address_of_packed_member (type, rhs);
+
+  if (context)
+    {
+      location_t loc = EXPR_LOC_OR_LOC (rhs, input_location);
+      warning_at (loc, OPT_Waddress_of_packed_member,
+		  "taking address of packed member of %qT may result "
+		  "in an unaligned pointer value",
+		  context);
+    }
+}
diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index a4c8c8ffcb3..a347f5e42c4 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -599,6 +599,10 @@  Wincompatible-pointer-types
 C ObjC Var(warn_incompatible_pointer_types) Init(1) Warning
 Warn when there is a conversion between pointers that have incompatible types.
 
+Waddress-of-packed-member
+C ObjC C++ ObjC++ Var(warn_address_of_packed_member) Init(1) Warning
+Warn when the address of packed member of struct or union is taken.
+
 Winit-self
 C ObjC C++ ObjC++ Var(warn_init_self) Warning LangEnabledBy(C++ ObjC++,Wall)
 Warn about variables which are initialized to themselves.
diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index 5b3ea28af06..3ed89e9c4b0 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -6289,6 +6289,54 @@  inform_for_arg (tree fundecl, location_t ploc, int parmnum,
 	  expected_type, actual_type);
 }
 
+/* Warn if the right hand poiner value RHS isn't aligned to a
+   pointer type TYPE.  ERRTYPE says whether it is argument passing,
+   assignment, initialization or return.  PARMNUM is the number of
+   the argument, for printing in error messages.  NAME is the name
+   of the function.  */
+
+static void
+warn_for_pointer_of_packed_member (location_t location, tree type,
+				   tree rhs)
+{
+  if (!warn_address_of_packed_member || !POINTER_TYPE_P (type))
+    return;
+
+  bool pointer_p;
+  tree rhstype;
+
+  /* Check the original type of LHS.  */
+  switch (TREE_CODE (rhs))
+    {
+    case PARM_DECL:
+    case VAR_DECL:
+      rhstype = TREE_TYPE (rhs);
+      pointer_p = POINTER_TYPE_P (rhstype);
+      break;
+    case NOP_EXPR:
+      rhs = TREE_OPERAND (rhs, 0);
+      if (TREE_CODE (rhs) == ADDR_EXPR)
+	rhs = TREE_OPERAND (rhs, 0);
+      rhstype = TREE_TYPE (rhs);
+      pointer_p = TREE_CODE (rhstype) == ARRAY_TYPE;
+      break;
+    default:
+      return;
+    }
+
+  if (pointer_p
+      && TYPE_PACKED (TREE_TYPE (rhstype)))
+    {
+      unsigned int type_align = TYPE_ALIGN (TREE_TYPE (type));
+      unsigned int rhs_align = TYPE_ALIGN (TREE_TYPE (rhstype));
+      if ((rhs_align % type_align) != 0)
+	warning_at (location, OPT_Waddress_of_packed_member,
+		    "taking value of packed %qT may result in an "
+		    "unaligned pointer value",
+		    rhstype);
+    }
+}
+
 /* Convert value RHS to type TYPE as preparation for an assignment to
    an lvalue of type TYPE.  If ORIGTYPE is not NULL_TREE, it is the
    original type of RHS; this differs from TREE_TYPE (RHS) for enum
@@ -6499,7 +6547,10 @@  convert_for_assignment (location_t location, location_t expr_loc, tree type,
     }
 
   if (TYPE_MAIN_VARIANT (type) == TYPE_MAIN_VARIANT (rhstype))
-    return rhs;
+    {
+      warn_for_address_of_packed_member (type, orig_rhs);
+      return rhs;
+    }
 
   if (coder == VOID_TYPE)
     {
@@ -6986,6 +7037,13 @@  convert_for_assignment (location_t location, location_t expr_loc, tree type,
 	    }
 	}
 
+      /* If LHS is't an address, check pointer or array of packed
+	 struct or union.  */
+      if (TREE_CODE (orig_rhs) != ADDR_EXPR)
+	warn_for_pointer_of_packed_member (location, type, orig_rhs);
+      else
+	warn_for_address_of_packed_member (type, orig_rhs);
+
       return convert (type, rhs);
     }
   else if (codel == POINTER_TYPE && coder == ARRAY_TYPE)
diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index fb6d71d260d..841a67ea007 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -7446,6 +7446,9 @@  convert_for_arg_passing (tree type, tree val, tsubst_flags_t complain)
 	}
       maybe_warn_parm_abi (type, EXPR_LOC_OR_LOC (val, input_location));
     }
+
+  warn_for_address_of_packed_member (type, val);
+
   return val;
 }
 
diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index 907d31d9786..2d3f78d2e8a 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -8903,6 +8903,8 @@  convert_for_assignment (tree type, tree rhs,
       TREE_NO_WARNING (rhs) = 1;
     }
 
+  warn_for_address_of_packed_member (type, rhs);
+
   return perform_implicit_conversion_flags (strip_top_quals (type), rhs,
 					    complain, flags);
 }
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 9c7fe187f48..cdd29c9ff0d 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -260,8 +260,8 @@  Objective-C and Objective-C++ Dialects}.
 @xref{Warning Options,,Options to Request or Suppress Warnings}.
 @gccoptlist{-fsyntax-only  -fmax-errors=@var{n}  -Wpedantic @gol
 -pedantic-errors @gol
--w  -Wextra  -Wall  -Waddress  -Waggregate-return  @gol
--Walloc-zero  -Walloc-size-larger-than=@var{n}
+-w  -Wextra  -Wall  -Waddress -Waddress-of-packed-member @gol
+-Waggregate-return -Walloc-zero -Walloc-size-larger-than=@var{n} @gol
 -Walloca  -Walloca-larger-than=@var{n} @gol
 -Wno-aggressive-loop-optimizations  -Warray-bounds  -Warray-bounds=@var{n} @gol
 -Wno-attributes  -Wbool-compare  -Wbool-operation @gol
@@ -6469,6 +6469,13 @@  behavior and are not portable in C, so they usually indicate that the
 programmer intended to use @code{strcmp}.  This warning is enabled by
 @option{-Wall}.
 
+@item -Waddress-of-packed-member
+@opindex Waddress-of-packed-member
+@opindex Wno-address-of-packed-member
+Warn when the address of packed member of struct or union is taken,
+which usually results in an unaligned pointer value.  This is
+enabled by default.
+
 @item -Wlogical-op
 @opindex Wlogical-op
 @opindex Wno-logical-op
diff --git a/gcc/testsuite/c-c++-common/asan/misalign-1.c b/gcc/testsuite/c-c++-common/asan/misalign-1.c
index 5cd605ac045..ebeb0306706 100644
--- a/gcc/testsuite/c-c++-common/asan/misalign-1.c
+++ b/gcc/testsuite/c-c++-common/asan/misalign-1.c
@@ -1,5 +1,5 @@ 
 /* { dg-do run { target { ilp32 || lp64 } } } */
-/* { dg-skip-if "" { *-*-* }  { "*" } { "-O2" } } */
+/* { dg-skip-if "" { *-*-* }  { "*" } { "-O2 -Wno-address-of-packed-member" } } */
 /* { dg-additional-options "-fno-omit-frame-pointer" { target *-*-darwin* } } */
 /* { dg-shouldfail "asan" } */
 
diff --git a/gcc/testsuite/c-c++-common/asan/misalign-2.c b/gcc/testsuite/c-c++-common/asan/misalign-2.c
index a6ed49bac05..b27e22d35a8 100644
--- a/gcc/testsuite/c-c++-common/asan/misalign-2.c
+++ b/gcc/testsuite/c-c++-common/asan/misalign-2.c
@@ -1,5 +1,5 @@ 
 /* { dg-do run { target { ilp32 || lp64 } } } */
-/* { dg-skip-if "" { *-*-* }  { "*" } { "-O2" } } */
+/* { dg-skip-if "" { *-*-* }  { "*" } { "-O2 -Wno-address-of-packed-member" } } */
 /* { dg-additional-options "-fno-omit-frame-pointer" { target *-*-darwin* } } */
 /* { dg-shouldfail "asan" } */
 
diff --git a/gcc/testsuite/c-c++-common/pr51628-1.c b/gcc/testsuite/c-c++-common/pr51628-1.c
new file mode 100644
index 00000000000..5324f9cc964
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr51628-1.c
@@ -0,0 +1,29 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+struct pair_t
+{
+  int x;
+  int i;
+} __attribute__((packed, aligned (4)));
+
+extern struct pair_t p;
+extern int *x;
+extern void bar (int *);
+
+int *addr = &p.i;
+
+int *
+foo (void)
+{
+  struct pair_t arr[2] = { { 1, 10 }, { 2, 20 } };
+  int *p0, *p1;
+  p0 = &arr[0].i;
+  bar (p0);
+  p1 = &arr[1].i;
+  bar (p1);
+  bar (&p.i);
+  x = &p.i;
+  return &p.i;
+}
diff --git a/gcc/testsuite/c-c++-common/pr51628-10.c b/gcc/testsuite/c-c++-common/pr51628-10.c
new file mode 100644
index 00000000000..085fe1608c4
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr51628-10.c
@@ -0,0 +1,24 @@ 
+/* PR c/51628.  */
+/* { dg-do run { target int128 } } */
+/* { dg-options "-O2" } */
+
+struct pair_t
+{
+  char c;
+  __int128_t i;
+} __attribute__ ((packed));
+
+typedef struct unaligned_int128_t_
+{
+  __int128_t value;
+} __attribute__((packed)) unaligned_int128_t;
+
+struct pair_t p = {0, 1};
+unaligned_int128_t *addr = (unaligned_int128_t *) &p.i;
+
+int 
+main() 
+{
+  addr->value = ~(__int128_t)0;
+  return (p.i != 1) ? 0 : 1;
+}
diff --git a/gcc/testsuite/c-c++-common/pr51628-11.c b/gcc/testsuite/c-c++-common/pr51628-11.c
new file mode 100644
index 00000000000..7661232ac88
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr51628-11.c
@@ -0,0 +1,17 @@ 
+/* PR c/51628.  */
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O" } */
+
+struct tuple_t
+{
+  char c[12];
+  __int128_t i;
+} __attribute__((packed, aligned (8)));
+
+typedef struct unaligned_int128_t_
+{
+  __int128_t value;
+} __attribute__ ((packed, aligned(4))) unaligned_int128_t;
+
+struct tuple_t p = {{0}, 1};
+unaligned_int128_t *addr = (unaligned_int128_t *)(&p.i);
diff --git a/gcc/testsuite/c-c++-common/pr51628-12.c b/gcc/testsuite/c-c++-common/pr51628-12.c
new file mode 100644
index 00000000000..bc221fa87ef
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr51628-12.c
@@ -0,0 +1,18 @@ 
+/* PR c/51628.  */
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O" } */
+
+struct tuple_t
+{
+  char c[10];
+  __int128_t i;
+} __attribute__((packed, aligned (8)));
+
+typedef struct unaligned_int128_t_
+{
+  __int128_t value;
+} __attribute__ ((packed, aligned(4))) unaligned_int128_t;
+
+struct tuple_t p = {{0}, 1};
+unaligned_int128_t *addr = (unaligned_int128_t *)(&p.i);
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
diff --git a/gcc/testsuite/c-c++-common/pr51628-13.c b/gcc/testsuite/c-c++-common/pr51628-13.c
new file mode 100644
index 00000000000..0edd5e7f84d
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr51628-13.c
@@ -0,0 +1,9 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+struct B { int i; };
+struct C { struct B b; } __attribute__ ((packed));
+
+int* h4 (struct C *p) { return &p->b.i; }
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
diff --git a/gcc/testsuite/c-c++-common/pr51628-14.c b/gcc/testsuite/c-c++-common/pr51628-14.c
new file mode 100644
index 00000000000..f50378b8651
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr51628-14.c
@@ -0,0 +1,9 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+struct A {
+  int i;
+} __attribute__ ((packed));
+
+void* f0 (struct A *p) { return &p->i; }
diff --git a/gcc/testsuite/c-c++-common/pr51628-15.c b/gcc/testsuite/c-c++-common/pr51628-15.c
new file mode 100644
index 00000000000..bcac6d70ad5
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr51628-15.c
@@ -0,0 +1,14 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+struct A {
+  int i;
+} __attribute__ ((packed));
+
+int*
+f (struct A *p, int *q)
+{
+  return q ? q : &p->i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+}
diff --git a/gcc/testsuite/c-c++-common/pr51628-2.c b/gcc/testsuite/c-c++-common/pr51628-2.c
new file mode 100644
index 00000000000..abfb84ddd05
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr51628-2.c
@@ -0,0 +1,29 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+struct pair_t
+{
+  int x;
+  int i;
+} __attribute__((packed, aligned (8)));
+
+extern struct pair_t p;
+extern int *x;
+extern void bar (int *);
+
+int *addr = &p.i;
+
+int *
+foo (void)
+{
+  struct pair_t arr[2] = { { 1, 10 }, { 2, 20 } };
+  int *p0, *p1;
+  p0 = &arr[0].i;
+  bar (p0);
+  p1 = &arr[1].i;
+  bar (p1);
+  bar (&p.i);
+  x = &p.i;
+  return &p.i;
+}
diff --git a/gcc/testsuite/c-c++-common/pr51628-3.c b/gcc/testsuite/c-c++-common/pr51628-3.c
new file mode 100644
index 00000000000..0ea94c845a0
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr51628-3.c
@@ -0,0 +1,35 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+struct pair_t
+{
+  int x;
+  int i;
+} __attribute__((packed, aligned (2)));
+
+extern struct pair_t p;
+extern int *x;
+extern void bar (int *);
+
+int *addr = &p.i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+
+int *
+foo (void)
+{
+  struct pair_t arr[2] = { { 1, 10 }, { 2, 20 } };
+  int *p0, *p1;
+  p0 = &arr[0].i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  bar (p0);
+  p1 = &arr[1].i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  bar (p1);
+  bar (&p.i);
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  x = &p.i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  return &p.i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+}
diff --git a/gcc/testsuite/c-c++-common/pr51628-4.c b/gcc/testsuite/c-c++-common/pr51628-4.c
new file mode 100644
index 00000000000..c4c1fb72d6d
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr51628-4.c
@@ -0,0 +1,35 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+struct pair_t
+{
+  int x;
+  int i;
+} __attribute__((packed));
+
+extern struct pair_t p;
+extern int *x;
+extern void bar (int *);
+
+int *addr = &p.i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+
+int *
+foo (void)
+{
+  struct pair_t arr[2] = { { 1, 10 }, { 2, 20 } };
+  int *p0, *p1;
+  p0 = &arr[0].i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  bar (p0);
+  p1 = &arr[1].i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  bar (p1);
+  bar (&p.i);
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  x = &p.i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  return &p.i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+}
diff --git a/gcc/testsuite/c-c++-common/pr51628-5.c b/gcc/testsuite/c-c++-common/pr51628-5.c
new file mode 100644
index 00000000000..9d7c309a0ef
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr51628-5.c
@@ -0,0 +1,35 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+struct pair_t
+{
+  char x;
+  int i;
+} __attribute__((packed));
+
+extern struct pair_t p;
+extern int *x;
+extern void bar (int *);
+
+int *addr = &p.i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+
+int *
+foo (void)
+{
+  struct pair_t arr[2] = { { 1, 10 }, { 2, 20 } };
+  int *p0, *p1;
+  p0 = &arr[0].i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  bar (p0);
+  p1 = &arr[1].i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  bar (p1);
+  bar (&p.i);
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  x = &p.i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  return &p.i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+}
diff --git a/gcc/testsuite/c-c++-common/pr51628-6.c b/gcc/testsuite/c-c++-common/pr51628-6.c
new file mode 100644
index 00000000000..52aa07a4cf3
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr51628-6.c
@@ -0,0 +1,35 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+struct pair_t
+{
+  char x;
+  int i;
+} __attribute__((packed, aligned (4)));
+
+extern struct pair_t p;
+extern int *x;
+extern void bar (int *);
+
+int *addr = &p.i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+
+int *
+foo (void)
+{
+  struct pair_t arr[2] = { { 1, 10 }, { 2, 20 } };
+  int *p0, *p1;
+  p0 = &arr[0].i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  bar (p0);
+  p1 = &arr[1].i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  bar (p1);
+  bar (&p.i);
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  x = &p.i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  return &p.i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+}
diff --git a/gcc/testsuite/c-c++-common/pr51628-7.c b/gcc/testsuite/c-c++-common/pr51628-7.c
new file mode 100644
index 00000000000..ae4a681f966
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr51628-7.c
@@ -0,0 +1,29 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+struct pair_t
+{
+  int x;
+  int i[4];
+} __attribute__((packed, aligned (4)));
+
+extern struct pair_t p;
+extern int *x;
+extern void bar (int *);
+
+int *addr = p.i;
+
+int *
+foo (struct pair_t *p)
+{
+  int *p0, *p1;
+  p0 = p->i;
+  bar (p0);
+  p1 = &p->i[1];
+  bar (p1);
+  bar (p->i);
+  bar (&p->i[2]);
+  x = p->i;
+  return &p->i[3];
+}
diff --git a/gcc/testsuite/c-c++-common/pr51628-8.c b/gcc/testsuite/c-c++-common/pr51628-8.c
new file mode 100644
index 00000000000..cc2dae096ae
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr51628-8.c
@@ -0,0 +1,36 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+struct pair_t
+{
+  char x;
+  int i[4];
+} __attribute__ ((packed, aligned (4)));
+
+extern struct pair_t p;
+extern int *x;
+extern void bar (int *);
+
+int *addr = p.i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+
+int *
+foo (struct pair_t *p)
+{
+  int *p0, *p1;
+  p0 = p->i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  bar (p0);
+  p1 = &p->i[1];
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  bar (p1);
+  bar (p->i);
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  bar (&p->i[2]);
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  x = p->i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  return &p->i[3];
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+}
diff --git a/gcc/testsuite/c-c++-common/pr51628-9.c b/gcc/testsuite/c-c++-common/pr51628-9.c
new file mode 100644
index 00000000000..0470aa3b93d
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/pr51628-9.c
@@ -0,0 +1,36 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+struct pair_t
+{
+  int x;
+  int i[4];
+} __attribute__ ((packed));
+
+extern struct pair_t p;
+extern int *x;
+extern void bar (int *);
+
+int *addr = p.i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+
+int *
+foo (struct pair_t *p)
+{
+  int *p0, *p1;
+  p0 = p->i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  bar (p0);
+  p1 = &p->i[1];
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  bar (p1);
+  bar (p->i);
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  bar (&p->i[2]);
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  x = p->i;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  return &p->i[3];
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+}
diff --git a/gcc/testsuite/c-c++-common/ubsan/align-10.c b/gcc/testsuite/c-c++-common/ubsan/align-10.c
index 56ae9ebfe30..6210533173c 100644
--- a/gcc/testsuite/c-c++-common/ubsan/align-10.c
+++ b/gcc/testsuite/c-c++-common/ubsan/align-10.c
@@ -1,6 +1,6 @@ 
 /* Limit this to known non-strict alignment targets.  */
 /* { dg-do run { target { i?86-*-linux* x86_64-*-linux* } } } */
-/* { dg-options "-O -fsanitize=alignment -fsanitize-recover=alignment" } */
+/* { dg-options "-O -fsanitize=alignment -fsanitize-recover=alignment -Wno-address-of-packed-member" } */
 
 struct R { int a; } r;
 struct S { struct R a; char b; long long c; short d[10]; };
diff --git a/gcc/testsuite/c-c++-common/ubsan/align-2.c b/gcc/testsuite/c-c++-common/ubsan/align-2.c
index 071de8c202a..336b1c3c907 100644
--- a/gcc/testsuite/c-c++-common/ubsan/align-2.c
+++ b/gcc/testsuite/c-c++-common/ubsan/align-2.c
@@ -1,6 +1,6 @@ 
 /* Limit this to known non-strict alignment targets.  */
 /* { dg-do run { target { i?86-*-linux* x86_64-*-linux* } } } */
-/* { dg-options "-fsanitize=alignment" } */
+/* { dg-options "-fsanitize=alignment -Wno-address-of-packed-member" } */
 
 struct S { int a; char b; long long c; short d[10]; };
 struct T { char a; long long b; };
diff --git a/gcc/testsuite/c-c++-common/ubsan/align-4.c b/gcc/testsuite/c-c++-common/ubsan/align-4.c
index 3252595d330..d5feeee29c6 100644
--- a/gcc/testsuite/c-c++-common/ubsan/align-4.c
+++ b/gcc/testsuite/c-c++-common/ubsan/align-4.c
@@ -1,6 +1,6 @@ 
 /* Limit this to known non-strict alignment targets.  */
 /* { dg-do run { target { i?86-*-linux* x86_64-*-linux* } } } */
-/* { dg-options "-fsanitize=null,alignment" } */
+/* { dg-options "-fsanitize=null,alignment -Wno-address-of-packed-member" } */
 
 #include "align-2.c"
 
diff --git a/gcc/testsuite/c-c++-common/ubsan/align-6.c b/gcc/testsuite/c-c++-common/ubsan/align-6.c
index 3364746fb27..0302b7b8894 100644
--- a/gcc/testsuite/c-c++-common/ubsan/align-6.c
+++ b/gcc/testsuite/c-c++-common/ubsan/align-6.c
@@ -1,6 +1,6 @@ 
 /* Limit this to known non-strict alignment targets.  */
 /* { dg-do run { target { i?86-*-linux* x86_64-*-linux* } } } */
-/* { dg-options "-O -fsanitize=alignment -fsanitize-recover=alignment" } */
+/* { dg-options "-O -fsanitize=alignment -fsanitize-recover=alignment -Wno-address-of-packed-member" } */
 
 struct S { int a; char b; long long c; short d[10]; };
 struct T { char a; long long b; };
diff --git a/gcc/testsuite/c-c++-common/ubsan/align-7.c b/gcc/testsuite/c-c++-common/ubsan/align-7.c
index ec4e87f56d5..dd1e8c91cef 100644
--- a/gcc/testsuite/c-c++-common/ubsan/align-7.c
+++ b/gcc/testsuite/c-c++-common/ubsan/align-7.c
@@ -1,6 +1,6 @@ 
 /* Limit this to known non-strict alignment targets.  */
 /* { dg-do run { target { i?86-*-linux* x86_64-*-linux* } } } */
-/* { dg-options "-O -fsanitize=alignment -fno-sanitize-recover=alignment -fdump-tree-sanopt-details" } */
+/* { dg-options "-O -fsanitize=alignment -fno-sanitize-recover=alignment -Wno-address-of-packed-member -fdump-tree-sanopt-details" } */
 /* { dg-skip-if "" { *-*-* } { "-flto -fno-fat-lto-objects" } } */
 /* { dg-shouldfail "ubsan" } */
 
diff --git a/gcc/testsuite/c-c++-common/ubsan/align-8.c b/gcc/testsuite/c-c++-common/ubsan/align-8.c
index 61c1ceb6682..5fe0e0fe931 100644
--- a/gcc/testsuite/c-c++-common/ubsan/align-8.c
+++ b/gcc/testsuite/c-c++-common/ubsan/align-8.c
@@ -1,6 +1,6 @@ 
 /* Limit this to known non-strict alignment targets.  */
 /* { dg-do run { target { i?86-*-linux* x86_64-*-linux* } } } */
-/* { dg-options "-O -fsanitize=alignment -fsanitize-undefined-trap-on-error -fdump-tree-sanopt-details" } */
+/* { dg-options "-O -fsanitize=alignment -fsanitize-undefined-trap-on-error -Wno-address-of-packed-member -fdump-tree-sanopt-details" } */
 /* { dg-skip-if "" { *-*-* } { "-flto -fno-fat-lto-objects" } } */
 /* { dg-shouldfail "ubsan" } */
 
diff --git a/gcc/testsuite/g++.dg/ubsan/align-2.C b/gcc/testsuite/g++.dg/ubsan/align-2.C
index 3e4f5485d02..c97ede88392 100644
--- a/gcc/testsuite/g++.dg/ubsan/align-2.C
+++ b/gcc/testsuite/g++.dg/ubsan/align-2.C
@@ -1,6 +1,6 @@ 
 // Limit this to known non-strict alignment targets.
 // { dg-do run { target { i?86-*-linux* x86_64-*-linux* } } }
-// { dg-options "-fsanitize=alignment -Wall -Wno-unused-variable -std=c++11" }
+// { dg-options "-fsanitize=alignment -Wall -Wno-unused-variable -Wno-address-of-packed-member -std=c++11" }
 
 typedef const long int L;
 struct S { long int l; char buf[1 + sizeof (int) + sizeof (L)]; } s;
diff --git a/gcc/testsuite/gcc.dg/pr51628-16.c b/gcc/testsuite/gcc.dg/pr51628-16.c
new file mode 100644
index 00000000000..94a3a8fbaf2
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr51628-16.c
@@ -0,0 +1,9 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O -Wno-incompatible-pointer-types" } */
+
+struct B { int i; };
+struct C { struct B b; } __attribute__ ((packed));
+
+long* g8 (struct C *p) { return p; }
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
diff --git a/gcc/testsuite/gcc.dg/pr51628-17.c b/gcc/testsuite/gcc.dg/pr51628-17.c
new file mode 100644
index 00000000000..0be95b2294e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr51628-17.c
@@ -0,0 +1,10 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O -Wno-incompatible-pointer-types" } */
+
+struct A {
+  int i;
+} __attribute__ ((packed));
+
+long* f8 (struct A *p) { return &p->i; }
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
diff --git a/gcc/testsuite/gcc.dg/pr51628-18.c b/gcc/testsuite/gcc.dg/pr51628-18.c
new file mode 100644
index 00000000000..03a04eff75c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr51628-18.c
@@ -0,0 +1,23 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+void foo (int *);
+
+int *
+bar (int n, int k, void *ptr)
+{
+  struct A
+  {
+    int c[k];
+    int x[n];
+  } __attribute__ ((packed, aligned (4)));
+  struct A *p = (struct A *) ptr;
+
+  int *p0, *p1;
+  p0 = p->x;
+  foo (p0);
+  p1 = &p->x[1];
+  foo (p1);
+  return &p->x[1];
+}
diff --git a/gcc/testsuite/gcc.dg/pr51628-19.c b/gcc/testsuite/gcc.dg/pr51628-19.c
new file mode 100644
index 00000000000..7ff03e85cea
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr51628-19.c
@@ -0,0 +1,26 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+void foo (int *);
+
+int *
+bar (int n, int k, void *ptr)
+{
+  struct A
+  {
+    char c[k];
+    int x[n];
+  } __attribute__ ((packed));
+  struct A *p = (struct A *) ptr;
+
+  int *p0, *p1;
+  p0 = p->x;
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  foo (p0);
+  p1 = &p->x[1];
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+  foo (p1);
+  return &p->x[1];
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
+}
diff --git a/gcc/testsuite/gcc.dg/pr51628-20.c b/gcc/testsuite/gcc.dg/pr51628-20.c
new file mode 100644
index 00000000000..bcdbff1e554
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr51628-20.c
@@ -0,0 +1,11 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O -Wno-incompatible-pointer-types" } */
+
+struct B { int i; };
+struct C { struct B b; } __attribute__ ((packed));
+
+extern struct C *p;
+
+long* g8 (void) { return p; }
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
diff --git a/gcc/testsuite/gcc.dg/pr51628-21.c b/gcc/testsuite/gcc.dg/pr51628-21.c
new file mode 100644
index 00000000000..0c7fab75d8a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr51628-21.c
@@ -0,0 +1,11 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O -Wno-incompatible-pointer-types" } */
+
+struct B { int i; };
+struct C { struct B b; } __attribute__ ((packed));
+
+extern struct C p[];
+
+long* g8 (void) { return p; }
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
diff --git a/gcc/testsuite/gcc.dg/pr51628-22.c b/gcc/testsuite/gcc.dg/pr51628-22.c
new file mode 100644
index 00000000000..1bd5d791639
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr51628-22.c
@@ -0,0 +1,9 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O -Wno-incompatible-pointer-types" } */
+
+struct B { int i; };
+struct C { struct B b; } __attribute__ ((packed));
+
+int* g4 (struct C *p) { return &p->b; }
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
diff --git a/gcc/testsuite/gcc.dg/pr51628-23.c b/gcc/testsuite/gcc.dg/pr51628-23.c
new file mode 100644
index 00000000000..5709be60ac8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr51628-23.c
@@ -0,0 +1,9 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O -Wno-incompatible-pointer-types" } */
+
+struct A {
+  int i;
+} __attribute__ ((packed));
+
+char* f0 (struct A *p) { return &p->i; }
diff --git a/gcc/testsuite/gcc.dg/pr51628-24.c b/gcc/testsuite/gcc.dg/pr51628-24.c
new file mode 100644
index 00000000000..3ad99cd2f16
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr51628-24.c
@@ -0,0 +1,10 @@ 
+/* PR c/51628.  */
+/* { dg-do compile } */
+/* { dg-options "-O -Wno-incompatible-pointer-types" } */
+
+struct A {
+  int i;
+} __attribute__ ((packed));
+
+short* f2 (struct A *p) { return &p->i; }
+/* { dg-warning "may result in an unaligned pointer value" "" { target *-*-* } .-1 } */
diff --git a/gcc/testsuite/gcc.target/i386/avx512bw-vmovdqu16-2.c b/gcc/testsuite/gcc.target/i386/avx512bw-vmovdqu16-2.c
index a61609c40d2..c6e3ebdc507 100644
--- a/gcc/testsuite/gcc.target/i386/avx512bw-vmovdqu16-2.c
+++ b/gcc/testsuite/gcc.target/i386/avx512bw-vmovdqu16-2.c
@@ -1,5 +1,5 @@ 
 /* { dg-do run } */
-/* { dg-options "-O2 -mavx512bw" } */
+/* { dg-options "-O2 -mavx512bw -Wno-address-of-packed-member" } */
 /* { dg-require-effective-target avx512bw } */
 
 #define AVX512BW
diff --git a/gcc/testsuite/gcc.target/i386/avx512f-vmovdqu32-2.c b/gcc/testsuite/gcc.target/i386/avx512f-vmovdqu32-2.c
index f2edc3dff7b..95a657fc5ff 100644
--- a/gcc/testsuite/gcc.target/i386/avx512f-vmovdqu32-2.c
+++ b/gcc/testsuite/gcc.target/i386/avx512f-vmovdqu32-2.c
@@ -1,5 +1,5 @@ 
 /* { dg-do run } */
-/* { dg-options "-O2 -mavx512f" } */
+/* { dg-options "-O2 -mavx512f -Wno-address-of-packed-member" } */
 /* { dg-require-effective-target avx512f } */
 
 #define AVX512F
diff --git a/gcc/testsuite/gcc.target/i386/avx512f-vmovdqu64-2.c b/gcc/testsuite/gcc.target/i386/avx512f-vmovdqu64-2.c
index 14176965ace..954b091d976 100644
--- a/gcc/testsuite/gcc.target/i386/avx512f-vmovdqu64-2.c
+++ b/gcc/testsuite/gcc.target/i386/avx512f-vmovdqu64-2.c
@@ -1,5 +1,5 @@ 
 /* { dg-do run } */
-/* { dg-options "-O2 -mavx512f" } */
+/* { dg-options "-O2 -mavx512f -Wno-address-of-packed-member" } */
 /* { dg-require-effective-target avx512f } */
 
 #define AVX512F
diff --git a/gcc/testsuite/gcc.target/i386/avx512vl-vmovdqu16-2.c b/gcc/testsuite/gcc.target/i386/avx512vl-vmovdqu16-2.c
index 45ae83d4552..81465f8d9a0 100644
--- a/gcc/testsuite/gcc.target/i386/avx512vl-vmovdqu16-2.c
+++ b/gcc/testsuite/gcc.target/i386/avx512vl-vmovdqu16-2.c
@@ -1,5 +1,5 @@ 
 /* { dg-do run } */
-/* { dg-options "-O2 -mavx512bw -mavx512vl" } */
+/* { dg-options "-O2 -mavx512bw -mavx512vl -Wno-address-of-packed-member" } */
 /* { dg-require-effective-target avx512vl } */
 /* { dg-require-effective-target avx512bw } */
 
diff --git a/gcc/testsuite/gcc.target/i386/avx512vl-vmovdqu32-2.c b/gcc/testsuite/gcc.target/i386/avx512vl-vmovdqu32-2.c
index 4b928d0cd42..19390664bd0 100644
--- a/gcc/testsuite/gcc.target/i386/avx512vl-vmovdqu32-2.c
+++ b/gcc/testsuite/gcc.target/i386/avx512vl-vmovdqu32-2.c
@@ -1,5 +1,5 @@ 
 /* { dg-do run } */
-/* { dg-options "-O2 -mavx512vl" } */
+/* { dg-options "-O2 -mavx512vl -Wno-address-of-packed-member" } */
 /* { dg-require-effective-target avx512vl } */
 
 #define AVX512VL
diff --git a/gcc/testsuite/gcc.target/i386/avx512vl-vmovdqu64-2.c b/gcc/testsuite/gcc.target/i386/avx512vl-vmovdqu64-2.c
index 1863ed3616f..aea0c12a5ff 100644
--- a/gcc/testsuite/gcc.target/i386/avx512vl-vmovdqu64-2.c
+++ b/gcc/testsuite/gcc.target/i386/avx512vl-vmovdqu64-2.c
@@ -1,5 +1,5 @@ 
 /* { dg-do run } */
-/* { dg-options "-O2 -mavx512vl" } */
+/* { dg-options "-O2 -mavx512vl -Wno-address-of-packed-member" } */
 /* { dg-require-effective-target avx512vl } */
 
 #define AVX512VL
diff --git a/libgcc/unwind-pe.h b/libgcc/unwind-pe.h
index dd5ae95fc2c..05c2fb4dd50 100644
--- a/libgcc/unwind-pe.h
+++ b/libgcc/unwind-pe.h
@@ -177,6 +177,9 @@  read_sleb128 (const unsigned char *p, _sleb128_t *val)
    The function returns P incremented past the value.  BASE is as given
    by base_of_encoded_value for this encoding in the appropriate context.  */
 
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Waddress-of-packed-member"
+
 static const unsigned char *
 read_encoded_value_with_base (unsigned char encoding, _Unwind_Ptr base,
 			      const unsigned char *p, _Unwind_Ptr *val)
@@ -270,6 +273,8 @@  read_encoded_value_with_base (unsigned char encoding, _Unwind_Ptr base,
   return p;
 }
 
+#pragma GCC diagnostic pop
+
 #ifndef NO_BASE_OF_ENCODED_VALUE
 
 /* Like read_encoded_value_with_base, but get the base from the context