On Fri, Dec 07, 2012 at 11:36:40AM -0500, Steven Rostedt wrote: > On Fri, 2012-12-07 at 16:23 +0000, Russell King - ARM Linux wrote: > > > That's fine if there are better ways. If your view is that this would > > bring things "up to the future" consider this: what you suggest is possible > > with the standard ARM 32-bit instruction set. With the more modern Thumb > > instruction set, because we now effectively have prefixes, where those > > prefixes control the execution of the following instructions, what you > > suggest becomes no longer possible. > > > > So, it's not a question of bringing stuff up to the future at all... you > > can call it a design regression of you will, but you're really making > > demands about how CPUs work which are outside of your remit. > > > > Think of this a bit like you changing the opcodes immediately following a > > 'LOCK' prefix on x86. I suspect divorsing the following opcodes from its > > prefix would be very bad for the instructions atomicity. > > But what about the limitations that the function tracer imposes on the > code that gets modified by stop_machine()? > > 1) the original code is simply a call to mcount > > 2) on boot up, that call gets converted into a nop > > 3) the code that gets changed will only be converting a nop to a call > into the function tracer, and back again. > > IOW, it's a very limited subset of the ARM assembly that gets touched. > I'm not sure what the op codes are for the above, but I can imagine they > don't impose the prefixes as you described. > > If that's the case, is it still possible to change to the breakpoint > method?
I have no idea; I've no idea how ftrace works on ARM. That's something other people use and deal with. Last (and only) time I used the built-in kernel tracing facilities I ended up giving up with it and going back to using my sched-clock+record+printk based approaches instead on account of the kernels built-in tracing being far too heavy. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
