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The SPARC assembly is often hard to understand because a single
instruction will show up as not executed. The instructions before
and after it will be marked as executed. The instruction before
the one not executed should be a "bxx,a" instruction which means
that the instruction following the branch instruction is executed
ONLY if the branch is taken. Otherwise it is "annulled" or skipped.
So when you see these cases, it means the branch was NOT taken.
===================================================================
Subject: <offlist> annul slot explanation
From: Jiri Gaisler <jiri@gaisler.com>
Date: Wed, 3 Jun 2009 14:57:48 -0500
To: Joel Sherrill <Joel.Sherrill@OARcorp.com>
Joel Sherrill wrote:
> > Hi,
> >
> > I am trying to look at more coverage cases and
> > wanted to make sure I am reading things correctly.
> >
> > The code in question is:
> >
> >
> > if ( the_thread->current_priority > interested_priority )
> > 200fd00: d8 00 e0 14 ld [ %g3 + 0x14 ], %o4
> > 200fd04: 80 a3 00 04 cmp %o4, %g4
> > 200fd08: 38 80 00 1c bgu,a 200fd78 <killinfo+0x224>
> > 200fd0c: 98 10 00 04 mov %g4,
> > %o4 <== NOT EXECUTED
> >
> > /*
> > * If this thread is not interested, then go on to the next thread.
> > */
> >
> > api = the_thread->API_Extensions[ THREAD_API_POSIX ];
> > 200fd10: d4 00 e1 6c ld [ %g3 + 0x16c ], %o2
> >
> > Am I correct in interpreting this as meaning 0x200fd0c
> > is not executed because the bgu,a is never taken. And it
> > is not executed as part of falling through.
Yes, this is correct. The branch delay slot is only executed
when the branch is taken.
Jiri.
> >
> > So in this case we need a test where the "if" condition
> > is true if I am reading things correctly.
> >
> > Thanks. There are a number of these 4 byte cases which
> > are probably easy to hit if I read the code correctly.
> >
> >
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