From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-477993-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 7431 invoked by alias); 20 Feb 2015 19:09:09 -0000
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
Received: (qmail 7136 invoked by uid 48); 20 Feb 2015 19:09:05 -0000
From: "alexey.lapshin at oracle dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/65145] New: size of atomic object is not correct
Date: Fri, 20 Feb 2015 19:48:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c
X-Bugzilla-Version: 4.9.2
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: alexey.lapshin at oracle dot com
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags:
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status bug_severity priority component assigned_to reporter
Message-ID: <bug-65145-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-SW-Source: 2015-02/txt/msg02325.txt.bz2

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65145

            Bug ID: 65145
           Summary: size of atomic object is not correct
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: alexey.lapshin at oracle dot com

The size of atomic object does not match with documentation -
https://gcc.gnu.org/wiki/Atomic/GCCMM/UnalignedPolicy specifically : 

"GCC 4.9 will provide an atomic type attribute which can be set on objects. 
This attribute will force a specific alignment and size on the object which may
be different than the original data type. The alignment and size will attempt
to provide lock free operations, if they exist. ... An object will be promoted
up to the next lock-free size in order to enable lock free operations, as long
as it isn't already a documented lock free size. "

~/atomic_test$ cat non_power_2_atomic.c 

#include <stdatomic.h>
#include <stdio.h>

typedef struct {
    char c [5];
} non_power_to_obj;

int main ( void ) {

    non_power_to_obj obj;
    _Atomic non_power_to_obj aobj;

    printf("\n Size and Alignment usual object "); 
    printf(" : sizeof(obj) %d __alignof__(obj) %d ", sizeof(obj),
__alignof__(obj) );

    printf("\n Size and Alignment of atomic object "); 
    printf(" : sizeof(aobj) %d __alignof__(aobj) %d \n", sizeof(aobj),
__alignof__(aobj) );

    return 0;
}

~/atomic_test$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/opt/gcc/libexec/gcc/i386-pc-solaris2.11/4.9.2/lto-wrapper
Target: i386-pc-solaris2.11
Configured with: ./configure --prefix=/opt/gcc/
Thread model: posix
gcc version 4.9.2 (GCC) 


~/atomic_test$ gcc -O -latomic -std=c11 non_power_2_atomic.c

~/atomic_test$ ./a.out

 Size and Alignment usual object  : sizeof(obj) 5 __alignof__(obj) 1 
 Size and Alignment of atomic object  : sizeof(aobj) 5 __alignof__(aobj) 1 

According to the https://gcc.gnu.org/wiki/Atomic/GCCMM/UnalignedPolicy
the size and alignment of "aobj" should be 8.

The bug us found on Solaris x86, but it could be on other platforms
also(SPARC/Linux). This bug is also exist in g++.