[PATCH] make softirq.* probes work on older kernels

[Bryn M. Reeves]

Hi Folks,

Hit the following bug in the irq tapset while putting a probe on the
softirq entry/exit trace points:

# stap -e 'probe softirq.entry { print("foo\n") } probe softirq.exit {
print("bar\n") }'
semantic error: no match while resolving probe point softirq.entry
semantic error: no match while resolving probe point softirq.exit
Pass 2: analysis failed.  Try again with another '--vp 01' option.

irq.stp is using the new names for these functions:
# egrep 'softirq_(entry|exit)' /usr/share/systemtap/tapset/irq.stp
probe softirq.entry = kernel.trace("softirq_entry") ?
probe softirq.exit = kernel.trace("softirq_exit") ?

But RHEL5 kernels still call them irq_softirq_entry/irq_softirq_exit:

# stap -L 'kernel.trace("*")' | egrep 'softirq_(entry|exit)'
kernel.trace("irq_softirq_entry") $h:struct softirq_action*
$softirq_vec:struct softirq_action*
kernel.trace("irq_softirq_exit") $h:struct softirq_action*
$softirq_vec:struct softirq_action*

The attached patch seems to be working ok for me.

Cheers,
Bryn.
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