On Fri, May 11, 2007 at 10:27:29AM +0530, Ananth N Mavinakayanahalli wrote: > On Thu, May 10, 2007 at 12:59:18PM -0400, Mathieu Desnoyers wrote: > > * Alan Cox ([EMAIL PROTECTED]) wrote: > > ... > > > > * Third issue : Scalability. Changing code will stop every CPU on the > > > > system for a while. Compared to this, the int3-based approach will run > > > > through the breakpoint handler "if" one of the CPU happens to execute > > > > this code at the wrong time. The standard case is just an IPI (to > > > > > > If I read the errata right then patching in an int3 will itself trigger > > > the errata so anything could happen. > > > > > > I believe there are other safe sequences for doing code patching - perhaps > > > one of the Intel folk can advise ? > > IIRC, when the first implementation of what exists now as kprobes was > done (as part of the dprobes framework), this question did come up. I > think the conclusion was that the errata applies only to multi-byte > modifications and single-byte changes are guaranteed to be atomic. > Given int3 on Intel is just 1-byte, we are safe. > > > I'll let the Intel guys confirm this, I don't have the reference nearby > > (I got this information by talking with the kprobe team members, and > > they got this information directly from Intel developers) but the > > int3 is the one special case to which the errata does not apply. > > Otherwise, kprobes and gdb would have a big, big issue. > > Perhaps Richard/Suparna can confirm.
I just tried digging up past discussions on this from Richard, about int3 being safe http://sourceware.org/ml/systemtap/2005-q3/msg00208.html http://lkml.org/lkml/2006/9/20/30 Regards Suparna > > Ananth -- Suparna Bhattacharya ([EMAIL PROTECTED]) Linux Technology Center IBM Software Lab, India - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/