From 00aa1fa221744dc57f6c6cea8baa669b732d1101 Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Fri, 18 Aug 2017 09:38:38 +0000 Subject: Add warn_if_not_aligned attribute Add warn_if_not_aligned attribute as well as command line options: -Wif-not-aligned and -Wpacked-not-aligned. __attribute__((warn_if_not_aligned(N))) causes compiler to issue 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 This warning is controlled by -Wif-not-aligned and is enabled by default. When -Wpacked-not-aligned is used, the same warning is also issued 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 This warning is disabled by default and enabled by -Wall. gcc/ PR c/53037 * print-tree.c (print_node): Support DECL_WARN_IF_NOT_ALIGN and TYPE_WARN_IF_NOT_ALIGN. * stor-layout.c (do_type_align): Merge DECL_WARN_IF_NOT_ALIGN. (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-core.h (tree_type_common): Add warn_if_not_align. Set spare to 18. (tree_decl_common): Add warn_if_not_align. * tree.c (build_range_type_1): Copy TYPE_WARN_IF_NOT_ALIGN. * tree.h (TYPE_WARN_IF_NOT_ALIGN): New. (SET_TYPE_WARN_IF_NOT_ALIGN): Likewise. (DECL_WARN_IF_NOT_ALIGN): Likewise. (SET_DECL_WARN_IF_NOT_ALIGN): Likewise. * doc/extend.texi: Document warn_if_not_aligned attribute. * doc/invoke.texi: Document -Wif-not-aligned and -Wpacked-not-aligned. gcc/c-family/ PR c/53037 * 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.opt: Add -Wif-not-aligned and -Wpacked-not-aligned. gcc/c/ PR c/53037 * c-decl.c (merge_decls): Also merge DECL_WARN_IF_NOT_ALIGN. (check_bitfield_type_and_width): Don't allow bit-field with warn_if_not_aligned type. gcc/cp/ PR c/53037 * decl.c (duplicate_decls): Also merge DECL_WARN_IF_NOT_ALIGN. * decl2.c (grokbitfield): Don't allow bit-field with warn_if_not_aligned type. gcc/testsuite/ PR c/53037 * c-c++-common/pr53037-5.c: New test. * g++.dg/pr53037-1.C: Likewise. * g++.dg/pr53037-2.C: Likewise. * g++.dg/pr53037-3.C: Likewise. * g++.dg/pr53037-4.C: Likewise. * gcc.dg/pr53037-1.c: Likewise. * gcc.dg/pr53037-2.c: Likewise. * gcc.dg/pr53037-3.c: Likewise. * gcc.dg/pr53037-4.c: Likewise. From-SVN: r251180 --- gcc/tree.h | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) (limited to 'gcc/tree.h') diff --git a/gcc/tree.h b/gcc/tree.h index 1f3cf1a..9fbf640 100644 --- a/gcc/tree.h +++ b/gcc/tree.h @@ -1919,6 +1919,16 @@ 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 @@ -2371,6 +2381,16 @@ extern machine_mode element_mode (const_tree t); #define SET_DECL_ALIGN(NODE, X) \ (DECL_COMMON_CHECK (NODE)->decl_common.align = ffs_hwi (X)) +/* The minimum alignment necessary for the datum, in bits, without + warning. */ +#define DECL_WARN_IF_NOT_ALIGN(NODE) \ + (DECL_COMMON_CHECK (NODE)->decl_common.warn_if_not_align \ + ? ((unsigned)1) << ((NODE)->decl_common.warn_if_not_align - 1) : 0) + +/* Specify that DECL_WARN_IF_NOT_ALIGN(NODE) is X. */ +#define SET_DECL_WARN_IF_NOT_ALIGN(NODE, X) \ + (DECL_COMMON_CHECK (NODE)->decl_common.warn_if_not_align = ffs_hwi (X)) + /* The alignment of NODE, in bytes. */ #define DECL_ALIGN_UNIT(NODE) (DECL_ALIGN (NODE) / BITS_PER_UNIT) /* Set if the alignment of this DECL has been set by the user, for -- cgit v1.1