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* c++/8464: Bus Error (SIGBUS) due to misaligned access
@ 2002-11-05 8:26 kyle_s_hoyt
0 siblings, 0 replies; 3+ messages in thread
From: kyle_s_hoyt @ 2002-11-05 8:26 UTC (permalink / raw)
To: gcc-gnats
>Number: 8464
>Category: c++
>Synopsis: Bus Error (SIGBUS) due to misaligned access
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: wrong-code
>Submitter-Id: net
>Arrival-Date: Tue Nov 05 08:26:00 PST 2002
>Closed-Date:
>Last-Modified:
>Originator: Kyle Hoyt
>Release: 2.95.2 19991024
>Organization:
>Environment:
SunOS 2.6 Generic_108528-06 sun4u sparc SUNW,Ultra-250
>Description:
Copying of data from a pointer results in a SIGBUS error.
Basically, the compiler is generating a ldd instruction
when the data is not guaranteed to be 8-byte aligned.
I have tried to multiple options such as the __attribute__
((aligned)); but I can not get the compiler not to
create the ldd instruction.
>How-To-Repeat:
Compile the included code and run. Basically, this is
a real stripped down version of the program. The program
receives Navigation Data messages via a data tape. The
message is guarranteed to be 4 byte aligned but not 8 byte.
The ProcessNav routine stores a history of the navigation
data. Thus it copies the message and puts it in a FIFO.
The code works on Pentium (G++ complier) and PowerPC
(GreenHills compiler) platforms but not on Sparc.
>Fix:
Change the code to use bcopy.
>Release-Note:
>Audit-Trail:
>Unformatted:
----gnatsweb-attachment----
Content-Type: text/plain; name="gccbug.txt"
Content-Disposition: inline; filename="gccbug.txt"
typedef struct
{
int message;
int numwords;
double latitude;
double longitude;
double altitude;
double ew_rate;
double ns_rate;
int time;
} NAVIGATION_DATAS __attribute__ ((aligned(4)));
void ProcessNavData(NAVIGATION_DATAS *nav_ptr)
{
NAVIGATION_DATAS store;
store = *nav_ptr;
}
int main()
{
unsigned int data[1024];
ProcessNavData((NAVIGATION_DATAS *)&data[0]);
ProcessNavData((NAVIGATION_DATAS *)&data[1]);
}
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: c++/8464: Bus Error (SIGBUS) due to misaligned access
@ 2002-11-05 8:49 bangerth
0 siblings, 0 replies; 3+ messages in thread
From: bangerth @ 2002-11-05 8:49 UTC (permalink / raw)
To: gcc-bugs, gcc-prs, kyle_s_hoyt, nobody
Synopsis: Bus Error (SIGBUS) due to misaligned access
State-Changed-From-To: open->closed
State-Changed-By: bangerth
State-Changed-When: Tue Nov 5 08:49:44 2002
State-Changed-Why:
Confirmed with 2.95, but does not happen with 3.0 any more.
3.2 rejects the code for other reasons.
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=8464
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: c++/8464: Bus Error (SIGBUS) due to misaligned access
@ 2002-11-05 9:16 Andreas Schwab
0 siblings, 0 replies; 3+ messages in thread
From: Andreas Schwab @ 2002-11-05 9:16 UTC (permalink / raw)
To: nobody; +Cc: gcc-prs
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The following reply was made to PR c++/8464; it has been noted by GNATS.
From: Andreas Schwab <schwab@suse.de>
To: kyle_s_hoyt@raytheon.com
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: c++/8464: Bus Error (SIGBUS) due to misaligned access
Date: Tue, 05 Nov 2002 18:10:46 +0100
kyle_s_hoyt@raytheon.com writes:
|> typedef struct
|> {
|> int message;
|> int numwords;
|> double latitude;
|> double longitude;
|> double altitude;
|> double ew_rate;
|> double ns_rate;
|> int time;
|> } NAVIGATION_DATAS __attribute__ ((aligned(4)));
|>
|> void ProcessNavData(NAVIGATION_DATAS *nav_ptr)
|> {
|> NAVIGATION_DATAS store;
|>
|> store = *nav_ptr;
|> }
|>
|> int main()
|> {
|> unsigned int data[1024];
|>
|> ProcessNavData((NAVIGATION_DATAS *)&data[0]);
|> ProcessNavData((NAVIGATION_DATAS *)&data[1]);
|> }
This is invoking undefined behavior. The aligned attribute by itself
cannot _decrease_ the alignment, only _increase_ it (ie. it specifies a
minimum alignment). You have to add packed as well.
Andreas.
--
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux AG, Deutschherrnstr. 15-19, D-90429 Nürnberg
Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."
^ permalink raw reply [flat|nested] 3+ messages in thread
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