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* c/9110: Zero-length bitfields cause wider structure when -fpack-struct is specified
@ 2002-12-30 16:46 etiotto
0 siblings, 0 replies; 2+ messages in thread
From: etiotto @ 2002-12-30 16:46 UTC (permalink / raw)
To: gcc-gnats
>Number: 9110
>Category: c
>Synopsis: Zero-length bitfields cause wider structure when -fpack-struct is specified
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: sw-bug
>Submitter-Id: net
>Arrival-Date: Mon Dec 30 16:46:00 PST 2002
>Closed-Date:
>Last-Modified:
>Originator: Ettore Tiotto
>Release: gcc-3.2
>Organization:
>Environment:
powerpc-suse-linux
>Description:
When the -fpack-struct command line option is used, a zero-length bitfield
of type short causes padding to the next 4-byte boundary, and makes the
structure size greater than the one it has when -fpack-struct is not
specified.
>How-To-Repeat:
Consider the following structure:
struct A {
int a;
short :0;
int b:15;
};
without -fpack-struct, the structure layout is:
aaaaaaaa ........ bbbbbbbb bbbbbbb.
the zero-length bit-field of type short caused member b to be mapped at offset 2
from the beginning of the structure. The structure has size 4 bytes.
With -fpack-struct the structure layout is:
aaaaaaaa ........ ........ ........ bbbbbbbb bbbbbbb.
Member b is now mapped at offset 4 and the structure occupies 6 bytes.
When -fpack-struct is specified I would expect the structure to occupies
3 bytes, with no padding between members a and b:
aaaaaaaa bbbbbbbb bbbbbbb.
or alternativelly to have the same layout as without -fpack-struct.
Whichever layout is choosen, the structure size should not be greater
than 4 bytes.
Note: with -fpack-struct specified, member b is mapped at offset 4 even when
it is a bitfield of type char, int or long. Strange enough when member b
has long long type and -fpack-struct is specified, b has offset 8.
>Fix:
>Release-Note:
>Audit-Trail:
>Unformatted:
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: c/9110: Zero-length bitfields cause wider structure when -fpack-struct is specified
@ 2003-01-03 10:56 Christian Ehrhardt
0 siblings, 0 replies; 2+ messages in thread
From: Christian Ehrhardt @ 2003-01-03 10:56 UTC (permalink / raw)
To: nobody; +Cc: gcc-prs
The following reply was made to PR c/9110; it has been noted by GNATS.
From: "Christian Ehrhardt" <ehrhardt@mathematik.uni-ulm.de>
To: gcc-gnats@gcc.gnu.org, gcc-prs@gcc.gnu.org, gcc-bugs@gcc.gnu.org,
nobody@gcc.gnu.org, etiotto@ca.ibm.com
Cc:
Subject: Re: c/9110: Zero-length bitfields cause wider structure when -fpack-struct is specified
Date: Fri, 3 Jan 2003 11:46:46 +0100
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=9110
Some discussion about this PR got picked up by GNATS as PR 9141 and PR 9142.
The executive summary is:
a) Mark probably fixed this but someone has to verify on power-pc or build
a cross compiler.
b) The code snipped in the test case is is wrong, field a should habe type
char.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2002-12-30 16:46 c/9110: Zero-length bitfields cause wider structure when -fpack-struct is specified etiotto
2003-01-03 10:56 Christian Ehrhardt
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