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Ability to disable 32-byte alignment of bss/data symbols with size > 32 bytes
- From: Yuly Finkelberg <yuly dot finkelberg at gmail dot com>
- To: gcc-help <gcc-help at gcc dot gnu dot org>
- Date: Wed, 29 Apr 2009 10:45:44 -0400
- Subject: Ability to disable 32-byte alignment of bss/data symbols with size > 32 bytes
Hi - I have the following test program:
struct
{
int arr[10];
} mycomm ;
int arr_bss[10] ;
int arr_data[10] = {1} ;
Compiling it with '-S' using gcc 4.3.2 under Linux (x86) shows that
each of the three symbols gets aligned on a 32 *BYTE* boundary.
...
.comm mycomm,40,32
.comm arr_bss,40,32
.align 32
.type arr_data, @object
.size arr_data, 40
If I pass "-Os", the alignments drop to 4 bytes (as expected);
"__attribute__ ((aligned(4))" also works. However, I'd very much like
a way to control this behavior globally without getting everything
else that "-Os" comes with. A "-f" switch perhaps? I was able to
find http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30004, which appears
to have relaxed the alignment under "-Os" specifically.
For what it's worth, GCC 4.3.2 on Solaris 10 (sparc) emits 4-byte
alignment. Also, sun's studio 12 compiler on Linux (x86) does the
same.
Thanks in advance.