Environment:
AIX 4.3.3 - RS6000 H80 - VAC 5.0.2.0

Has anyone had data alignment problems when using
pthreads while compiling a program with the
"-qalign=packed" directive ????

Is this a known problem???

Our specific problem was in a pthread_mutex_trylock() call
.....it incorrectly reports the mutex is locked...
unless we force the pthread_mutex_t onto a full-word alignment...
....then it works correctly.

Are there other "subsystems" that have a similar problem ???

THANKS,
-tony

Nicholas Dronen wrote:
> T.R.Bennett <bennett.tony@cnf.com> wrote:
> TRB> Has anyone had data alignment problems when using
> TRB> pthreads while compiling a program with the
> TRB> "-qalign=packed" directive ????

Sounds like the system include files should incorporate
wrappers that undo any alignment chosen by the user...

> TRB> Our specific problem was in a pthread_mutex_trylock() call
> TRB> ....it incorrectly reports the mutex is locked...
> TRB> unless we force the pthread_mutex_t onto a full-word alignment...
> TRB> ...then it works correctly.
>
> Whose problem it is depends on whether the mistake happens in the
> code (bad assumptions, bad data or variable access methods, whatnot)
> or the compiler (invalid behavior for pragma). You don't say under
> what exact circumstances the problem occurs. Do you have a small
> testcase that you can use to debug the problem outside of your
> application? If so, you have a chance to gather some information
> that might be useful for you or the vendor.
>
> And if the behavior disappears when you wrap your pthread code in
> '#pragma options align=reset', you're one step closer to knowing
> who to blame. :-)

It would probably make more sense to "stack" the pragma for
system structures, then "pop" back to the prior behavior.

> Small testcase. Try using 'reset'. Post what happens. Gary Hook,
> AKA Superfly of Linking, will respond. Eventually all will be well.
> (And Gary works for free. How much better can it get? :-)

Yeah, but I'm setting up a 1-900 number :-)

The packing pragma would nominally be applied to all of the code.
Unfortunately, certain system structures are going to have be
left alone. In this case, a lock had better be word aligned;
there are no options, no choices, no changes. Perhaps you
only need to wrap your structure definitions in the pack
pragma; the compiler should understand how to access the
members in that case, but that would leave the rest of the
system code alone.

--
Gary R. Hook / AIX PartnerWorld for Developers / These opinions are MINE
__________________________________________________ ______________________

"Gary R. Hook" <nospam@nospammers.net> wrote in message news:<vaq1b.3019$Cp4.696@newssvr22.news.prodigy.co m>...
> Nicholas Dronen wrote:
> > T.R.Bennett <bennett.tony@cnf.com> wrote:
> > TRB> Has anyone had data alignment problems when using
> > TRB> pthreads while compiling a program with the
> > TRB> "-qalign=packed" directive ????
>
> Sounds like the system include files should incorporate
> wrappers that undo any alignment chosen by the user...
>
> > TRB> Our specific problem was in a pthread_mutex_trylock() call
> > TRB> ....it incorrectly reports the mutex is locked...
> > TRB> unless we force the pthread_mutex_t onto a full-word alignment...
> > TRB> ...then it works correctly.
> >
> > Whose problem it is depends on whether the mistake happens in the
> > code (bad assumptions, bad data or variable access methods, whatnot)
> > or the compiler (invalid behavior for pragma). You don't say under
> > what exact circumstances the problem occurs. Do you have a small
> > testcase that you can use to debug the problem outside of your
> > application? If so, you have a chance to gather some information
> > that might be useful for you or the vendor.
> >
> > And if the behavior disappears when you wrap your pthread code in
> > '#pragma options align=reset', you're one step closer to knowing
> > who to blame. :-)
>
> It would probably make more sense to "stack" the pragma for
> system structures, then "pop" back to the prior behavior.
>
> > Small testcase. Try using 'reset'. Post what happens. Gary Hook,
> > AKA Superfly of Linking, will respond. Eventually all will be well.
> > (And Gary works for free. How much better can it get? :-)
>
> Yeah, but I'm setting up a 1-900 number :-)
>
> The packing pragma would nominally be applied to all of the code.
> Unfortunately, certain system structures are going to have be
> left alone. In this case, a lock had better be word aligned;
> there are no options, no choices, no changes. Perhaps you
> only need to wrap your structure definitions in the pack
> pragma; the compiler should understand how to access the
> members in that case, but that would leave the rest of the
> system code alone.


Gary,

Thanks for the info.

Am I correct in my understanding that I should NOT use the "-qalign=packed"
compiler argument but instead should put "#pragma option align=packed"
in my source or include file before any structure I wish to have
packed, and follow those structures with a "#pragma option align=reset" ??

Also, am I correct in assuming that the "-qalign=packed" compiler command
line argument will override any "#pragma option align=-" directives
in my source and/or include files ???

-tony

T.R.Bennett wrote:
> Am I correct in my understanding that I should NOT use the "-qalign=packed"
> compiler argument but instead should put "#pragma option align=packed"
> in my source or include file before any structure I wish to have
> packed, and follow those structures with a "#pragma option align=reset" ??

It is my understanding that this is the preferred technique.

> Also, am I correct in assuming that the "-qalign=packed" compiler command
> line argument will override any "#pragma option align=-" directives
> in my source and/or include files ???

I'd have to read the docs, but I would think this would be correct.

--
Gary R. Hook / AIX PartnerWorld for Developers / These opinions are MINE
__________________________________________________ ______________________