__attribute__((warn_if_not_aligned(N))) issues a warning if the field
in a struct or union is not aligned to N:
typedef unsigned long long __u64
__attribute__((aligned(4),warn_if_not_aligned(8)));
struct foo
{
int i1;
int i2;
__u64 x;
};
__u64 is aligned to 4 bytes. But inside struct foo, __u64 should be
aligned at 8 bytes. It is used to define struct foo in such a way that
struct foo has the same layout and x has the same alignment when __u64
is aligned at either 4 or 8 bytes.
Since struct foo is normally aligned to 4 bytes, a warning will be issued:
warning: alignment 4 of ‘struct foo’ is less than 8
Align struct foo to 8 bytes:
struct foo
{
int i1;
int i2;
__u64 x;
} __attribute__((aligned(8)));
silences the warning. It also warns the field with misaligned offset:
struct foo
{
int i1;
int i2;
int i3;
__u64 x;
} __attribute__((aligned(8)));
warning: ‘x’ offset 12 in ‘struct foo’ isn't aligned to 8
The same warning is also issued without the warn_if_not_aligned attribute
for the field with explicitly specified alignment in a packed struct or
union:
struct __attribute__ ((aligned (8))) S8 { char a[8]; };
struct __attribute__ ((packed)) S {
struct S8 s8;
};
warning: alignment 1 of ‘struct S’ is less than 8
gcc/
PR c/53037
* c-decl.c (finish_enum): Also copy TYPE_WARN_IF_NOT_ALIGN.
* print-tree.c (print_node): Support TYPE_WARN_IF_NOT_ALIGN.
* stor-layout.c (handle_warn_if_not_align): New.
(place_union_field): Call handle_warn_if_not_align.
(place_field): Call handle_warn_if_not_align. Copy
TYPE_WARN_IF_NOT_ALIGN.
(finish_builtin_struct): Copy TYPE_WARN_IF_NOT_ALIGN.
(layout_type): Likewise.
* tree.c (build_range_type_1): Likewise.
* tree-core.h (tree_type_common): Add warn_if_not_align. Set
spare to 18.
* tree.h (TYPE_WARN_IF_NOT_ALIGN): New.
(SET_TYPE_WARN_IF_NOT_ALIGN): Likewise.
* c-family/c-attribs.c (handle_warn_if_not_aligned_attribute): New.
(c_common_attribute_table): Add warn_if_not_aligned.
(handle_aligned_attribute): Renamed to ...
(common_handle_aligned_attribute): Remove argument, name, and add
argument, warn_if_not_aligned. Handle warn_if_not_aligned.
(handle_aligned_attribute): New.
* c/c-decl.c (finish_enum): Copy TYPE_WARN_IF_NOT_ALIGN.
gcc/testsuite/
PR c/53037
* gcc.dg/pr53037-1.c: New test.
---
gcc/c-family/c-attribs.c | 55 +++++++++++++++++++++++++++++++++----
gcc/c/c-decl.c | 2 ++
gcc/print-tree.c | 6 ++--
gcc/stor-layout.c | 45 ++++++++++++++++++++++++++++++
gcc/testsuite/gcc.dg/pr53037-1.c | 59 ++++++++++++++++++++++++++++++++++++++++
gcc/tree-core.h | 3 +-
gcc/tree.c | 1 +
gcc/tree.h | 10 +++++++
8 files changed, 172 insertions(+), 9 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/pr53037-1.c
diff --git a/gcc/c-family/c-attribs.c b/gcc/c-family/c-attribs.c
index 695c58c..a76f9f7 100644
--- a/gcc/c-family/c-attribs.c
+++ b/gcc/c-family/c-attribs.c
@@ -85,6 +85,8 @@ static tree handle_destructor_attribute (tree *, tree, tree,
int, bool *);
static tree handle_mode_attribute (tree *, tree, tree, int, bool *);
static tree handle_section_attribute (tree *, tree, tree, int, bool *);
static tree handle_aligned_attribute (tree *, tree, tree, int, bool *);
+static tree handle_warn_if_not_aligned_attribute (tree *, tree, tree,
+ int, bool *);
static tree handle_weak_attribute (tree *, tree, tree, int, bool *) ;
static tree handle_noplt_attribute (tree *, tree, tree, int, bool *) ;
static tree handle_alias_ifunc_attribute (bool, tree *, tree, tree, bool *);
@@ -208,6 +210,9 @@ const struct attribute_spec c_common_attribute_table[] =
handle_section_attribute, false },
{ "aligned", 0, 1, false, false, false,
handle_aligned_attribute, false },
+ { "warn_if_not_aligned", 0, 1, false, false, false,
+ handle_warn_if_not_aligned_attribute,
+ false },
{ "weak", 0, 0, true, false, false,
handle_weak_attribute, false },
{ "noplt", 0, 0, true, false, false,
@@ -1558,12 +1563,13 @@ check_cxx_fundamental_alignment_constraints (tree node,
return !alignment_too_large_p;
}
-/* Handle a "aligned" attribute; arguments as in
- struct attribute_spec.handler. */
+/* Common codes shared by handle_warn_if_not_aligned_attribute and
+ handle_aligned_attribute. */
static tree
-handle_aligned_attribute (tree *node, tree ARG_UNUSED (name), tree args,
- int flags, bool *no_add_attrs)
+common_handle_aligned_attribute (tree *node, tree args, int flags,
+ bool *no_add_attrs,
+ bool warn_if_not_aligned)
{
tree decl = NULL_TREE;
tree *type = NULL;
@@ -1612,8 +1618,16 @@ handle_aligned_attribute (tree *node, tree ARG_UNUSED
(name), tree args,
else
*type = build_variant_type_copy (*type);
- SET_TYPE_ALIGN (*type, (1U << i) * BITS_PER_UNIT);
- TYPE_USER_ALIGN (*type) = 1;
+ if (warn_if_not_aligned)
+ {
+ SET_TYPE_WARN_IF_NOT_ALIGN (*type, (1U << i) * BITS_PER_UNIT);
+ warn_if_not_aligned = false;
+ }
+ else
+ {
+ SET_TYPE_ALIGN (*type, (1U << i) * BITS_PER_UNIT);
+ TYPE_USER_ALIGN (*type) = 1;
+ }
}
else if (! VAR_OR_FUNCTION_DECL_P (decl)
&& TREE_CODE (decl) != FIELD_DECL)
@@ -1650,9 +1664,38 @@ handle_aligned_attribute (tree *node, tree ARG_UNUSED
(name), tree args,
DECL_USER_ALIGN (decl) = 1;
}
+ if (warn_if_not_aligned)
+ {
+ error ("warn_if_not_aligned may not be specified for %q+D", decl);
+ *no_add_attrs = true;
+ }
+
return NULL_TREE;
}
+/* Handle a "aligned" attribute; arguments as in
+ struct attribute_spec.handler. */
+
+static tree
+handle_aligned_attribute (tree *node, tree ARG_UNUSED (name), tree args,
+ int flags, bool *no_add_attrs)
+{
+ return common_handle_aligned_attribute (node, args, flags,
+ no_add_attrs, false);
+}
+
+/* Handle a "warn_if_not_aligned" attribute; arguments as in
+ struct attribute_spec.handler. */
+
+static tree
+handle_warn_if_not_aligned_attribute (tree *node, tree ARG_UNUSED (name),
+ tree args, int flags,
+ bool *no_add_attrs)
+{
+ return common_handle_aligned_attribute (node, args, flags,
+ no_add_attrs, true);
+}
+
/* Handle a "weak" attribute; arguments as in
struct attribute_spec.handler. */
diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
index f2b8096..f27356b 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -8363,6 +8363,8 @@ finish_enum (tree enumtype, tree values, tree attributes)
TYPE_PRECISION (tem) = TYPE_PRECISION (enumtype);
SET_TYPE_ALIGN (tem, TYPE_ALIGN (enumtype));
TYPE_USER_ALIGN (tem) = TYPE_USER_ALIGN (enumtype);
+ SET_TYPE_WARN_IF_NOT_ALIGN (tem,
+ TYPE_WARN_IF_NOT_ALIGN (enumtype));
TYPE_UNSIGNED (tem) = TYPE_UNSIGNED (enumtype);
TYPE_LANG_SPECIFIC (tem) = TYPE_LANG_SPECIFIC (enumtype);
}
diff --git a/gcc/print-tree.c b/gcc/print-tree.c
index ea26a0b..7b53c49 100644
--- a/gcc/print-tree.c
+++ b/gcc/print-tree.c
@@ -603,8 +603,10 @@ print_node (FILE *file, const char *prefix, tree node, int
indent,
if (TYPE_USER_ALIGN (node))
fprintf (file, " user");
- fprintf (file, " align %d symtab %d alias set " HOST_WIDE_INT_PRINT_DEC,
- TYPE_ALIGN (node), TYPE_SYMTAB_ADDRESS (node),
+ fprintf (file, " align %d warn_if_not_align %d symtab %d alias set "
+ HOST_WIDE_INT_PRINT_DEC,
+ TYPE_ALIGN (node), TYPE_WARN_IF_NOT_ALIGN (node),
+ TYPE_SYMTAB_ADDRESS (node),
(HOST_WIDE_INT) TYPE_ALIAS_SET (node));
if (TYPE_STRUCTURAL_EQUALITY_P (node))
diff --git a/gcc/stor-layout.c b/gcc/stor-layout.c
index 1574e43..28249bc 100644
--- a/gcc/stor-layout.c
+++ b/gcc/stor-layout.c
@@ -1074,6 +1074,38 @@ update_alignment_for_field (record_layout_info rli, tree
field,
return desired_align;
}
+static void
+handle_warn_if_not_align (tree field, unsigned int record_align)
+{
+ tree type = TREE_TYPE (field);
+
+ if (type == error_mark_node)
+ return;
+
+ unsigned int warn_if_not_align = TYPE_WARN_IF_NOT_ALIGN (type);
+
+ if (!warn_if_not_align && TYPE_USER_ALIGN (type))
+ warn_if_not_align = TYPE_ALIGN (type);
+
+ if (!warn_if_not_align)
+ return;
+
+ tree context = DECL_CONTEXT (field);
+
+ warn_if_not_align /= BITS_PER_UNIT;
+ record_align /= BITS_PER_UNIT;
+ if ((record_align % warn_if_not_align) != 0)
+ warning (0, "alignment %d of %qT is less than %d",
+ record_align, context, warn_if_not_align);
+
+ unsigned int off
+ = (tree_to_uhwi (DECL_FIELD_OFFSET (field))
+ + tree_to_uhwi (DECL_FIELD_BIT_OFFSET (field)) / BITS_PER_UNIT);
+ if ((off % warn_if_not_align) != 0)
+ warning (0, "%q+D offset %d in %qT isn't aligned to %d",
+ field, off, context, warn_if_not_align);
+}
+
/* Called from place_field to handle unions. */
static void
@@ -1084,6 +1116,7 @@ place_union_field (record_layout_info rli, tree field)
DECL_FIELD_OFFSET (field) = size_zero_node;
DECL_FIELD_BIT_OFFSET (field) = bitsize_zero_node;
SET_DECL_OFFSET_ALIGN (field, BIGGEST_ALIGNMENT);
+ handle_warn_if_not_align (field, rli->record_align);
/* If this is an ERROR_MARK return *after* having set the
field at the start of the union. This helps when parsing
@@ -1169,6 +1202,7 @@ place_field (record_layout_info rli, tree field)
DECL_FIELD_OFFSET (field) = rli->offset;
DECL_FIELD_BIT_OFFSET (field) = rli->bitpos;
SET_DECL_OFFSET_ALIGN (field, rli->offset_align);
+ handle_warn_if_not_align (field, rli->record_align);
return;
}
@@ -1290,6 +1324,9 @@ place_field (record_layout_info rli, tree field)
if (! DECL_PACKED (field))
TYPE_USER_ALIGN (rli->t) |= TYPE_USER_ALIGN (type);
+
+ SET_TYPE_WARN_IF_NOT_ALIGN (rli->t,
+ TYPE_WARN_IF_NOT_ALIGN (type));
}
#ifdef BITFIELD_NBYTES_LIMITED
@@ -1328,6 +1365,8 @@ place_field (record_layout_info rli, tree field)
rli->bitpos = round_up (rli->bitpos, type_align);
TYPE_USER_ALIGN (rli->t) |= TYPE_USER_ALIGN (type);
+ SET_TYPE_WARN_IF_NOT_ALIGN (rli->t,
+ TYPE_WARN_IF_NOT_ALIGN (type));
}
#endif
@@ -1478,6 +1517,7 @@ place_field (record_layout_info rli, tree field)
DECL_FIELD_OFFSET (field) = rli->offset;
DECL_FIELD_BIT_OFFSET (field) = rli->bitpos;
SET_DECL_OFFSET_ALIGN (field, rli->offset_align);
+ handle_warn_if_not_align (field, rli->record_align);
/* Evaluate nonconstant offsets only once, either now or as soon as safe. */
if (TREE_CODE (DECL_FIELD_OFFSET (field)) != INTEGER_CST)
@@ -2088,6 +2128,8 @@ finish_builtin_struct (tree type, const char *name, tree
fields,
{
SET_TYPE_ALIGN (type, TYPE_ALIGN (align_type));
TYPE_USER_ALIGN (type) = TYPE_USER_ALIGN (align_type);
+ SET_TYPE_WARN_IF_NOT_ALIGN (type,
+ TYPE_WARN_IF_NOT_ALIGN (align_type));
}
layout_type (type);
@@ -2324,6 +2366,9 @@ layout_type (tree type)
align = MAX (align, TYPE_ALIGN (type));
else
TYPE_USER_ALIGN (type) = TYPE_USER_ALIGN (element);
+ if (!TYPE_WARN_IF_NOT_ALIGN (type))
+ SET_TYPE_WARN_IF_NOT_ALIGN (type,
+ TYPE_WARN_IF_NOT_ALIGN (element));
#ifdef ROUND_TYPE_ALIGN
align = ROUND_TYPE_ALIGN (type, align, BITS_PER_UNIT);
#else
diff --git a/gcc/testsuite/gcc.dg/pr53037-1.c b/gcc/testsuite/gcc.dg/pr53037-1.c
new file mode 100644
index 0000000..1ab1f86
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr53037-1.c
@@ -0,0 +1,59 @@
+/* PR c/53037. */
+/* { dg-do compile } */
+/* { dg-options "-O0" } */
+
+typedef unsigned long long __u64
+ __attribute__((aligned(4),warn_if_not_aligned(8)));
+
+struct foo1
+{
+ int i1;
+ int i2;
+ int i3;
+ __u64 x; /* { dg-warning "'x' offset 12 in 'struct foo1' isn't aligned to 8"
} */
+}; /* { dg-warning "alignment 4 of 'struct foo1' is less than 8" } */
+
+struct foo2
+{
+ int i1;
+ int i2;
+ int i3;
+ __u64 x; /* { dg-warning "'x' offset 12 in 'struct foo2' isn't aligned to 8"
} */
+} __attribute__((aligned(8)));
+
+struct foo3
+{
+ int i1;
+ int i3;
+ __u64 x;
+}; /* { dg-warning "alignment 4 of 'struct foo3' is less than 8" } */
+
+struct foo4
+{
+ int i1;
+ int i2;
+ __u64 x;
+} __attribute__((aligned(8)));
+
+union bar1
+{
+ int i1;
+ int i3;
+ __u64 x;
+}; /* { dg-warning "alignment 4 of 'union bar1' is less than 8" } */
+
+union bar2
+{
+ int i1;
+ int i3;
+ __u64 x;
+} __attribute__((aligned(8)));
+
+struct __attribute__ ((aligned (8))) S8 { char a[8]; };
+struct __attribute__ ((packed)) S0 {
+ struct S8 s8;
+}; /* { dg-warning "alignment 1 of 'struct S0' is less than 8" } */
+
+struct __attribute__ ((packed)) S1 {
+ long long ll;
+};
diff --git a/gcc/tree-core.h b/gcc/tree-core.h
index ea73477..0882bdc 100644
--- a/gcc/tree-core.h
+++ b/gcc/tree-core.h
@@ -1516,8 +1516,9 @@ struct GTY(()) tree_type_common {
so we need to store the value 32 (not 31, as we need the zero
as well), hence six bits. */
unsigned align : 6;
+ unsigned warn_if_not_align : 6;
unsigned typeless_storage : 1;
- unsigned spare : 24;
+ unsigned spare : 18;
alias_set_type alias_set;
tree pointer_to;
diff --git a/gcc/tree.c b/gcc/tree.c
index a58f9aa..66287ae 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -8303,6 +8303,7 @@ build_range_type_1 (tree type, tree lowval, tree highval,
bool shared)
TYPE_SIZE_UNIT (itype) = TYPE_SIZE_UNIT (type);
SET_TYPE_ALIGN (itype, TYPE_ALIGN (type));
TYPE_USER_ALIGN (itype) = TYPE_USER_ALIGN (type);
+ SET_TYPE_WARN_IF_NOT_ALIGN (itype, TYPE_WARN_IF_NOT_ALIGN (type));
if (!shared)
return itype;
diff --git a/gcc/tree.h b/gcc/tree.h
index c6e883c..7d9572e 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -1922,6 +1922,16 @@ extern machine_mode element_mode (const_tree t);
/* The alignment for NODE, in bytes. */
#define TYPE_ALIGN_UNIT(NODE) (TYPE_ALIGN (NODE) / BITS_PER_UNIT)
+/* The minimum alignment necessary for objects of this type without
+ warning. The value is an int, measured in bits. */
+#define TYPE_WARN_IF_NOT_ALIGN(NODE) \
+ (TYPE_CHECK (NODE)->type_common.warn_if_not_align \
+ ? ((unsigned)1) << ((NODE)->type_common.warn_if_not_align - 1) : 0)
+
+/* Specify that TYPE_WARN_IF_NOT_ALIGN(NODE) is X. */
+#define SET_TYPE_WARN_IF_NOT_ALIGN(NODE, X) \
+ (TYPE_CHECK (NODE)->type_common.warn_if_not_align = ffs_hwi (X))
+
/* If your language allows you to declare types, and you want debug info
for them, then you need to generate corresponding TYPE_DECL nodes.
These "stub" TYPE_DECL nodes have no name, and simply point at the
--
2.9.4
