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Re: Why does $$parms show value as "?"


On 2011-08-25, Josh Stone <jistone@redhat.com> wrote:
> On 08/25/2011 10:15 AM, Grant Edwards wrote:
>>[...]
>>   skb=?
>>   skb=?
>>   ^Csystemtap end
>>   # 
>> 
>> Why isn't systemtap printing the value of the parameter "skb"?
>
> This means that the debuginfo has defined this parameter, but we're
> unable to access it for some reason, most likely because gcc didn't
> output location information in the debuginfo.  The variable may not even
> exist at that point anymore due to optimization.  That function is so
> short that it quite likely has been inlined into its callers.
>
>> The module in question is built "out of tree" and then installed in 
>> /lib/modules/VERSION/misc, and according to "file" it's not stripped.
>
> Since this is out of tree, you could try building the module without
> optimization,

Good point.  I'll keep that in mind.

> and that should keep all variables around for your
> perusal.  Or it may be enough just to mark that function noinline.

Delcaring the function with the "noinline" keyword fixed the problem,
but turning down optimization is probably going to be needed as well
for other probes.

-- 
Grant Edwards               grant.b.edwards        Yow! Maybe I should have
                                  at               asked for my Neutron Bomb
                              gmail.com            in PAISLEY --


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