dtrace discuss - Jan 2008 - copyin not giving expected result

Hi,

I''m having C function

size_t mutt_iconv (iconv_t cd, char **inbuf, ...

I would like to print the inbuf using dtrace.

I was thinking to use something like

"PTR=copyin(arg1, 4); trace(copyinstr(PTR));" but it does not work for
me.

$ dtrace -32 -w -n ''pid14243::mutt_iconv:entry{printf("0x%x
", arg1); A=copyin(arg1,4); printf("0x%x ", ((unsigned int)A));
stop();}''
dtrace: description ''pid14243::mutt_iconv:entry'' matched 1
probe
dtrace: allowing destructive actions
CPU     ID                    FUNCTION:NAME
  0  75510                 mutt_iconv:entry 0x8045168 0x97aa7018
^C

However if I try to dereference the pointer in mdb:

pub 12:54 ~/test: mdb -p 14243
Loading modules: [ ld.so.1 libc.so.1 ]
> 0x8045168/X
0x8045168:      8e4c038
>
I get correct resutl 8e4c038. I''m a bit confused, what am I doing wrong
?

And alternatively, is there better way of getting char **inbuf, than twhice
manually copyin ?

Thanks

-- 
	Vlad
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Hi Tiller,
> If you dereference A does it give you what you want?
> 
> Try this (see the extra * added in the second printf ):
> 
> $ dtrace -32 -w -n ''pid14243::mutt_iconv:entry{printf("0x%x
", arg1); A=copyin(arg1,4); printf("0x%x ", *((unsigned int)A));
stop();}''
Yes, this is exactly where I made the mistake. copyin is returning
pointer to the ''scratch'' space, and not the buffer content
itself.

For the reference, the function looks like

pid$target::mutt_iconv:entry
{
        A=*(unsigned int*)copyin(arg1,4);
        printf("0x%x ", A); trace(copyinstr(A));
}
> .tiller
Thank you Tiller

-- 
	Vlad
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