Re: java/1305: GCJ ignores volatile modifier

Re: java/1305: GCJ ignores volatile modifier

[Dara Hazeghi]

The following reply was made to PR java/1305; it has been noted by GNATS.

From: Dara Hazeghi <dhazeghi@yahoo.com>
To: gcc-gnats@gcc.gnu.org
Cc:  
Subject: Re: java/1305: GCJ ignores volatile modifier
Date: Mon, 12 May 2003 11:02:16 -0700

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit- 
 trail&database=gcc&pr=1305
 
 Hans Boehm says:
 
 "I think 1305 still needs to remain open.  It's not clear that this can
 be fixed completely until JSR133 finishes its job, and it becomes clear
 what the Java memory model really is.  (I'm one of the participants,
 and we have been trying.  It's not easy.)"
 
 So this PR should stay open.
 
 Dara
 

Re: java/1305: GCJ ignores volatile modifier

[Dara Hazeghi]

The following reply was made to PR java/1305; it has been noted by GNATS.

From: Dara Hazeghi <dhazeghi@yahoo.com>
To: apbianco@gcc.gnu.org, gcc-gnats@gcc.gnu.org, jeff.sturm@appnet.com
Cc:  
Subject: Re: java/1305: GCJ ignores volatile modifier
Date: Sun, 11 May 2003 20:04:19 -0700

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit- 
 trail&database=gcc&pr=1305
 
 Hello,
 
 this problem was reported against gcc cvs (20000730). Would it be  
 possible to determine if it is still present in current 3.3 branch or  
 mainline, and update this report accordingly? Thanks,
 
 Dara
 

java/1305: GCJ ignores volatile modifier

[jeff.sturm]

>Number:         1305
>Category:       java
>Synopsis:       GCJ ignores volatile modifier
>Confidential:   no
>Severity:       serious
>Priority:       low
>Responsible:    apbianco
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Dec 20 12:18:51 PST 2000
>Closed-Date:    
>Last-Modified:  
>Originator:     jeff.sturm@appnet.com
>Release:        CVS trunk (071300)
>Organization:
>Environment:
Linux 2.2 SMP
>Description:
GCJ doesn't implement volatile behavior as outlined in
JLS ch. 17 (or at all, evidently).

Ch. 17 specifies that loads and stores of volatile variables
must be consistent, atomic and sequential.  On some
multiprocessors, gcj-compiled code fails all tests.

Bill Pugh and Doug Lea are credited with discovering this
disrepancy between the JLS and existing JVMs (all current
VMs including those from Sun fail some of the tests.)  This
test case and others are available on Bill's site:

http://www.cs.umd.edu/~pugh/java/memoryModel
>How-To-Repeat:
Run the attached program on a multiprocessor (SMP) host.
It will test for proper sequential access to volatile
variables.  Any inconsistencies will be reported to stdout.

I tested ReadAfterWrite on a quad-PPro running a Linux 2.2
SMP kernel.
>Fix:
Insert a store barrier instruction before and after volatile
loads and stores.

Note that atomic loads and stores of volatile doubles and
longs will be difficult to implement correctly on many
32-bit architectures, including x86.
>Release-Note:
>Audit-Trail:

Formerly PR gcj/284

>Unformatted:
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