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da77eace90
When address of packed member of struct or union is taken, it may result
in an unaligned pointer value. This patch adds -Waddress-of-packed-member
to check alignment at pointer assignment and warn unaligned address as
well as unaligned pointer:
$ cat x.i
struct pair_t
{
char c;
int i;
} __attribute__ ((packed));
extern struct pair_t p;
int *addr = &p.i;
$ gcc -O2 -S x.i
x.i:8:13: warning: taking address of packed member of ‘struct pair_t’ may result in an unaligned pointer value [-Waddress-of-packed-member]
8 | int *addr = &p.i;
| ^
$ cat c.i
struct B { int i; };
struct C { struct B b; } __attribute__ ((packed));
long* g8 (struct C *p) { return p; }
$ gcc -O2 -S c.i -Wno-incompatible-pointer-types
c.i: In function ‘g8’:
c.i:4:18: warning: converting a packed ‘struct C *’ pointer (alignment 1) to ‘long int *’ (alignment 8) may may result in an unaligned pointer value [-Waddress-of-packed-member]
4 | long* g8 (struct C *p) { return p; }
| ^
c.i:2:8: note: defined here
2 | struct C { struct B b; } __attribute__ ((packed));
| ^
$
This warning is enabled by default. Since read_encoded_value_with_base
in unwind-pe.h has
union unaligned
{
void *ptr;
unsigned u2 __attribute__ ((mode (HI)));
unsigned u4 __attribute__ ((mode (SI)));
unsigned u8 __attribute__ ((mode (DI)));
signed s2 __attribute__ ((mode (HI)));
signed s4 __attribute__ ((mode (SI)));
signed s8 __attribute__ ((mode (DI)));
} __attribute__((__packed__));
_Unwind_Internal_Ptr result;
and GCC warns:
gcc/libgcc/unwind-pe.h:210:37: warning: taking address of packed member of 'union unaligned' may result in an unaligned pointer value [-Waddress-of-packed-member]
result = (_Unwind_Internal_Ptr) u->ptr;
^
we need to add GCC pragma to ignore -Waddress-of-packed-member.
gcc/
PR c/51628
* doc/invoke.texi: Document -Wno-address-of-packed-member.
gcc/c-family/
PR c/51628
* c-common.h (warn_for_address_or_pointer_of_packed_member): New.
* c-warn.c (check_alignment_of_packed_member): New function.
(check_address_of_packed_member): Likewise.
(check_and_warn_address_of_packed_member): Likewise.
(warn_for_address_or_pointer_of_packed_member): Likewise.
* c.opt: Add -Wno-address-of-packed-member.
gcc/c/
PR c/51628
* c-typeck.c (convert_for_assignment): Call
warn_for_address_or_pointer_of_packed_member.
gcc/cp/
PR c/51628
* call.c (convert_for_arg_passing): Call
warn_for_address_or_pointer_of_packed_member.
* typeck.c (convert_for_assignment): Likewise.
gcc/testsuite/
PR c/51628
* c-c++-common/pr51628-1.c: New test.
* c-c++-common/pr51628-2.c: Likewise.
* c-c++-common/pr51628-3.c: Likewise.
* c-c++-common/pr51628-4.c: Likewise.
* c-c++-common/pr51628-5.c: Likewise.
* c-c++-common/pr51628-6.c: Likewise.
* c-c++-common/pr51628-7.c: Likewise.
* c-c++-common/pr51628-8.c: Likewise.
* c-c++-common/pr51628-9.c: Likewise.
* c-c++-common/pr51628-10.c: Likewise.
* c-c++-common/pr51628-11.c: Likewise.
* c-c++-common/pr51628-12.c: Likewise.
* c-c++-common/pr51628-13.c: Likewise.
* c-c++-common/pr51628-14.c: Likewise.
* c-c++-common/pr51628-15.c: Likewise.
* c-c++-common/pr51628-26.c: Likewise.
* c-c++-common/pr51628-27.c: Likewise.
* c-c++-common/pr51628-28.c: Likewise.
* c-c++-common/pr51628-29.c: Likewise.
* c-c++-common/pr51628-30.c: Likewise.
* c-c++-common/pr51628-31.c: Likewise.
* c-c++-common/pr51628-32.c: Likewise.
* gcc.dg/pr51628-17.c: Likewise.
* gcc.dg/pr51628-18.c: Likewise.
* gcc.dg/pr51628-19.c: Likewise.
* gcc.dg/pr51628-20.c: Likewise.
* gcc.dg/pr51628-21.c: Likewise.
* gcc.dg/pr51628-22.c: Likewise.
* gcc.dg/pr51628-23.c: Likewise.
* gcc.dg/pr51628-24.c: Likewise.
* gcc.dg/pr51628-25.c: Likewise.
* c-c++-common/asan/misalign-1.c: Add
-Wno-address-of-packed-member.
* c-c++-common/asan/misalign-2.c: Likewise.
* c-c++-common/ubsan/align-2.c: Likewise.
* c-c++-common/ubsan/align-4.c: Likewise.
* c-c++-common/ubsan/align-6.c: Likewise.
* c-c++-common/ubsan/align-7.c: Likewise.
* c-c++-common/ubsan/align-8.c: Likewise.
* c-c++-common/ubsan/align-10.c: Likewise.
* g++.dg/ubsan/align-2.C: Likewise.
* gcc.target/i386/avx512bw-vmovdqu16-2.c: Likewise.
* gcc.target/i386/avx512f-vmovdqu32-2.c: Likewise.
* gcc.target/i386/avx512f-vmovdqu64-2.c: Likewise.
* gcc.target/i386/avx512vl-vmovdqu16-2.c: Likewise.
* gcc.target/i386/avx512vl-vmovdqu32-2.c: Likewise.
* gcc.target/i386/avx512vl-vmovdqu64-2.c: Likewise.
libgcc/
* unwind-pe.h (read_encoded_value_with_base): Add GCC pragma
to ignore -Waddress-of-packed-member.
From-SVN: r267313
This directory contains the GNU Compiler Collection (GCC). The GNU Compiler Collection is free software. See the files whose names start with COPYING for copying permission. The manuals, and some of the runtime libraries, are under different terms; see the individual source files for details. The directory INSTALL contains copies of the installation information as HTML and plain text. The source of this information is gcc/doc/install.texi. The installation information includes details of what is included in the GCC sources and what files GCC installs. See the file gcc/doc/gcc.texi (together with other files that it includes) for usage and porting information. An online readable version of the manual is in the files gcc/doc/gcc.info*. See http://gcc.gnu.org/bugs/ for how to report bugs usefully. Copyright years on GCC source files may be listed using range notation, e.g., 1987-2012, indicating that every year in the range, inclusive, is a copyrightable year that could otherwise be listed individually.