Re: [RFC] Hardware Breakpoint support for systemtap translator

[Roland McGrath <roland@redhat.com>]

> 1. probe kernel.data(ADDRESS).write     {....}   : To probe writes at 
> the given address
> 2. probe kernel.data(ADDRESS).rw         {....}   : To probe read & 
> write access to the given address.
> 3. probe kernel.data("SYMBOL").write   {....}
> 4. probe kernel.data("SYMBOL").rw       {....}   : Similar to 1,2, but 
> using a symbol name as argument.

That is a nice start!  But what about dynamic uses?
i.e.

	probe kernel.function("foobar")
	{
	  w1 = watch $foo->bar
	}

	probe kernel.function.return("foobar")
	{
	  unwatch w1
	}

	probe watch.w1
	{
	  val = $$watch.baz # i.e. $foo->bar.baz
	}

or probably some entirely different syntax.  But I think you get the idea:
enable/disable dynamically-discovered addresses to trigger watchpoint
probes of some sort.  I think it would be really nice if the watch probe
could somehow be embedded in the enabling probe's context so it can use
$bar there and have those address translations taken at enable-time.

Also, what about specifying access-size for the watchpoint, on machines
where that can be done (i.e. x86)?


Thanks,
Roland