invoke.texi: Document -Wabi.

2002-08-27  Mark Mitchell  <mark@codesourcery.com>

	* doc/invoke.texi: Document -Wabi.

2002-08-27  Mark Mitchell  <mark@codesourcery.com>

	* cp-tree.h (warn_abi): Declare it.
	* decl.c (warn_abi): Define it.
	(cxx_decode_option): Set it.
	* class.c (layout_virtual_bases): Warn about bugs in G++ that
	result in incorrect object layouts.
	(layout_class_type): Likewise.

2002-08-27  Mark Mitchell  <mark@codesourcery.com>

	* testsuite/g++.dg/abi/bitfield5.C: New test.
	* testsuite/g++.dg/abi/vbase10.C: Likewise.

From-SVN: r56623

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 6cd1b836a755d4fdad09d2664e7ebedb2f43ceaf..4bd213dc7cc86b8e3ed7b49900b89f049a456981 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,7 @@
+2002-08-27  Mark Mitchell  <mark@codesourcery.com>
+
+       * doc/invoke.texi: Document -Wabi.
+       
 2002-08-23  David Edelsohn  <edelsohn@gnu.org>
 
         * config/rs6000/rs6000.c (rs6000_select_section): Treat

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 8e84fe6f62e53b55ebfec331701076a316f47549..e7c5b8c5316d9f14d768bd3917cb642fc0ce1f41 100644 (file)
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,12 @@
+2002-08-27  Mark Mitchell  <mark@codesourcery.com>
+
+       * cp-tree.h (warn_abi): Declare it.
+       * decl.c (warn_abi): Define it.
+       (cxx_decode_option): Set it.
+       * class.c (layout_virtual_bases): Warn about bugs in G++ that
+       result in incorrect object layouts.
+       (layout_class_type): Likewise.
+
 2002-08-22  Jason Merrill  <jason@redhat.com>
 
        PR c++/5607

diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index f655846e060c5ceb0a8081b3cb60157e5721e85e..2395d794bfc7118cf807720565738d046127e501 100644 (file)
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -4557,6 +4557,7 @@ layout_virtual_bases (t, offsets)
 {
   tree vbases, dsize;
   unsigned HOST_WIDE_INT eoc;
+  bool first_vbase = true;
 
   if (CLASSTYPE_N_BASECLASSES (t) == 0)
     return;
@@ -4584,6 +4585,7 @@ layout_virtual_bases (t, offsets)
 
       if (!TREE_VIA_VIRTUAL (vbases))
        continue;
+
       vbase = binfo_for_vbase (BINFO_TYPE (vbases), t);
 
       if (!BINFO_PRIMARY_P (vbase))
@@ -4601,7 +4603,6 @@ layout_virtual_bases (t, offsets)
          /* Add padding so that we can put the virtual base class at an
             appropriately aligned offset.  */
          dsize = round_up (dsize, desired_align);
-
          usize = size_binop (CEIL_DIV_EXPR, dsize, bitsize_unit_node);
 
          /* We try to squish empty virtual bases in just like
@@ -4629,11 +4630,30 @@ layout_virtual_bases (t, offsets)
                                              CLASSTYPE_SIZE (basetype)));
            }
 
+         /* If the first virtual base might have been placed at a
+            lower address, had we started from CLASSTYPE_SIZE, rather
+            than TYPE_SIZE, issue a warning.  There can be both false
+            positives and false negatives from this warning in rare
+            cases; to deal with all the possibilities would probably
+            require performing both layout algorithms and comparing
+            the results which is not particularly tractable.  */
+         if (warn_abi
+             && first_vbase
+             && tree_int_cst_lt (size_binop (CEIL_DIV_EXPR,
+                                             round_up (CLASSTYPE_SIZE (t),
+                                                       desired_align),
+                                             bitsize_unit_node),
+                                 BINFO_OFFSET (vbase)))
+           warning ("offset of virtual base `%T' is not ABI-compliant and may change in a future version of GCC",
+                    basetype);
+
          /* Keep track of the offsets assigned to this virtual base.  */
          record_subobject_offsets (BINFO_TYPE (vbase), 
                                    BINFO_OFFSET (vbase),
                                    offsets,
                                    /*vbases_p=*/0);
+
+         first_vbase = false;
        }
     }
 
@@ -4771,6 +4791,8 @@ layout_class_type (t, empty_p, vfuns_p, virtuals_p)
   /* Maps offsets (represented as INTEGER_CSTs) to a TREE_LIST of
      types that appear at that offset.  */
   splay_tree empty_base_offsets;
+  /* True if the last field layed out was a bit-field.  */
+  bool last_field_was_bitfield = false;
 
   /* Keep track of the first non-static data member.  */
   non_static_data_members = TYPE_FIELDS (t);
@@ -4860,6 +4882,18 @@ layout_class_type (t, empty_p, vfuns_p, virtuals_p)
       layout_nonempty_base_or_field (rli, field, NULL_TREE,
                                     empty_base_offsets, t);
 
+      /* If a bit-field does not immediately follow another bit-field,
+        and yet it starts in the middle of a byte, we have failed to
+        comply with the ABI.  */
+      if (warn_abi
+         && DECL_C_BIT_FIELD (field) 
+         && !last_field_was_bitfield
+         && !integer_zerop (size_binop (TRUNC_MOD_EXPR,
+                                        DECL_FIELD_BIT_OFFSET (field),
+                                        bitsize_unit_node)))
+       cp_warning_at ("offset of `%D' is not ABI-compliant and may change in a future version of GCC", 
+                      field);
+
       /* If we needed additional padding after this field, add it
         now.  */
       if (padding)
@@ -4877,6 +4911,8 @@ layout_class_type (t, empty_p, vfuns_p, virtuals_p)
                                         NULL_TREE, 
                                         empty_base_offsets, t);
        }
+
+      last_field_was_bitfield = DECL_C_BIT_FIELD (field);
     }
 
   /* It might be the case that we grew the class to allocate a

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 48b615bf8d790991ea00794445e04698ff8ed0ee..787114f492b4802e9502ec98d762593b88584802 100644 (file)
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -934,6 +934,11 @@ extern int flag_operator_names;
 
 extern int flag_gnu_binutils;
 
+/* Nonzero means warn about things that will change when compiling
+   with an ABI-compliant compiler.  */
+
+extern int warn_abi;
+
 /* Nonzero means warn about implicit declarations.  */
 
 extern int warn_implicit;

diff --git a/gcc/cp/decl2.c b/gcc/cp/decl2.c
index 499ff73b9f594fbb54331fd7b5e78e239b620058..09a30f4a007f51ed57749170777db5bbbde072b3 100644 (file)
--- a/gcc/cp/decl2.c
+++ b/gcc/cp/decl2.c
@@ -172,6 +172,11 @@ int flag_implicit_templates = 1;
 
 int flag_implicit_inline_templates = 1;
 
+/* Nonzero means warn about things that will change when compiling
+   with an ABI-compliant compiler.  */
+
+int warn_abi = 0;
+
 /* Nonzero means warn about implicit declarations.  */
 
 int warn_implicit = 1;
@@ -600,7 +605,9 @@ cxx_decode_option (argc, argv)
       if (p[0] == 'n' && p[1] == 'o' && p[2] == '-')
        setting = 0, p += 3;
 
-      if (!strcmp (p, "implicit"))
+      if (!strcmp (p, "abi"))
+       warn_abi = setting;
+      else if (!strcmp (p, "implicit"))
        warn_implicit = setting;
       else if (!strcmp (p, "long-long"))
        warn_long_long = setting;

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 0fbea884fa051ca34f2d9030ac0d7a301d93eb75..a3b53ed3822c543952b28b9109183818be228e56 100644 (file)
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -187,7 +187,7 @@ in the following sections.
 -fno-optional-diags  -fpermissive @gol
 -frepo  -fno-rtti  -fstats  -ftemplate-depth-@var{n} @gol
 -fuse-cxa-atexit  -fvtable-gc  -fno-weak  -nostdinc++ @gol
--fno-default-inline  -Wctor-dtor-privacy @gol
+-fno-default-inline -Wabi -Wctor-dtor-privacy @gol
 -Wnon-virtual-dtor  -Wreorder @gol
 -Weffc++  -Wno-deprecated @gol
 -Wno-non-template-friend  -Wold-style-cast @gol
@@ -211,7 +211,7 @@ in the following sections.
 @xref{Warning Options,,Options to Request or Suppress Warnings}.
 @gccoptlist{
 -fsyntax-only  -pedantic  -pedantic-errors @gol
--w  -W  -Wall  -Waggregate-return @gol
+-w  -W  -Wall -Waggregate-return @gol
 -Wcast-align  -Wcast-qual  -Wchar-subscripts  -Wcomment @gol
 -Wconversion  -Wno-deprecated-declarations @gol
 -Wdisabled-optimization  -Wdiv-by-zero  -Werror @gol
@@ -1551,6 +1551,58 @@ Do not assume @samp{inline} for functions defined inside a class scope.
 functions will have linkage like inline functions; they just won't be
 inlined by default.
 
+@item -Wabi @r{(C++ only)}
+@opindex Wabi
+Warn when G++ generates code that is probably not compatible with the
+vendor-neutral C++ ABI.  Although an effort has been made to warn about
+all such cases, there are probably some cases that are not warned about, 
+even though G++ is generating incompatible code.  There may also be
+cases where warnings are emitted even though the code that is generated
+will be compatible.
+
+You should rewrite your code to avoid these warnings if you are
+concerned about the fact that code generated by G++ may not be binary
+compatible with code generated by other compilers.
+
+The known incompatibilites at this point include:
+
+@itemize @bullet
+
+@item
+Incorrect handling of tail-padding for bit-fields.  G++ may attempt to
+pack data into the same byte as a base class.  For example:
+
+@smallexample
+struct A @{ virtual void f(); int f1 : 1; @};
+struct B : public A @{ int f2 : 1; @};
+@end smallexample
+
+@noindent
+In this case, G++ will place @code{B::f2} into the same byte
+as@code{A::f1}; other compilers will not.  You can avoid this problem 
+by explicitly padding @code{A} so that its size is a multiple of the
+byte size on your platform; that will cause G++ and other compilers to
+layout @code{B} identically.
+
+@item
+Incorrect handling of tail-padding for virtual bases.  G++ does not use
+tail padding when laying out virtual bases.  For example:
+
+@smallexample
+struct A @{ virtual void f(); char c1; @};
+struct B @{ B(); char c2; @};
+struct C : public A, public virtual B @{@};
+@end smallexample
+
+@noindent
+In this case, G++ will not place @code{B} into the tail-padding for
+@code{A}; other compilers will.  You can avoid this problem by
+explicitly padding @code{A} so that its size is a multiple of its
+alignment (ignoring virtual base classes); that will cause G++ and other
+compilers to layout @code{C} identically.
+
+@end itemize
+
 @item -Wctor-dtor-privacy @r{(C++ only)}
 @opindex Wctor-dtor-privacy
 Warn when a class seems unusable, because all the constructors or

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index b15075dbac50e3de23754115adcc1f5028b25ddb..d70091b663a492e43277a3fb77e62b9de9cd3599 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2002-08-27  Mark Mitchell  <mark@codesourcery.com>
+
+       * testsuite/g++.dg/abi/bitfield5.C: New test.
+       * testsuite/g++.dg/abi/vbase10.C: Likewise.
+       
 2002-08-15  Neil Booth  <neil@daikokuya.co.uk>
 
        * gcc.dg/cpp/_Pragma3.c, gcc.dg/cpp/vararg3.c, gcc.dg/cpp/vararg4.c: