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Re: profiling on sh
kewarken@qnx.com wrote:
>
> Given the delay slot, could one also do this?
>
> jsr @r0
> mov.l lab,r0
> .align 4
> .long .LP0
> lab:
> .long _mcount
Unfortunately not - the reason for having the delay slot is to allow
the processor time to go get the instructions at the target address,
so it needs to know the target address when it starts executing the jsr.
> I'm also wondering about the label 'lab'. Does that need to be done every
> time and does the label need to be unique? This profiling code is inserted
> with every function call so I'm wondering if there's some way to globally
> insert this.
The problem here is that the mov.l lab,r0 instruction is actually a
pc-relative load:
mov.l @(lab-($+4), pc), r0
and the value of lab-($+4) has to be in the range [0,512).
So you need to make sure that lab is close enough to this mov.l instruction.
The simplest and most _inefficient_ thing to do, it to have a unique copy of
the label and _mcount literal for each call. This will bulk the code out,
but you're already doing that with all the calls to _mcount. If you're really
concerned about code size, then the original trapa scheme is much more
space efficient.
> Both the arm and thumb just do a 'bl mcount' but that didn't look to me like
> the way functions were called on sh
Sorry - you're right. I'd forgotten that thumb does not need to
embed an address literal in the code in order to make a function call.
Steve.
--
Stephen Clarke, Principal Engineer, SuperH Inc.
Phone:1-408-922-4062, Fax:1-408-954-8507, mailto:Stephen.Clarke@st.com
Mail: SuperH Inc., 3801 Zanker Rd., San Jose, CA 95134, USA.