On Tue, Sep 20, 2011 at 02:12:25PM -0400, Christoph Hellwig wrote: > On Tue, Sep 20, 2011 at 06:13:10PM +0100, Stefan Hajnoczi wrote: > > You've probably thought of this but it would be nice to skip XOL for > > nops. This would be a common case with static probes (e.g. sdt.h) where > > the probe template includes a nop where we can easily plant int $0x3. > > Do we now have sdt.h support for uprobes? That's one of the killer > features that always seemed to get postponed. Not yet but it's a question of doing roughly what SystemTap does to parse the appropriate ELF sections and then putting those probes into uprobes. Masami looked at this and found that SystemTap sdt.h currently requires an extra userspace memory store in order to activate probes. Each probe has a "semaphore" 16-bit counter which applications may test before hitting the probe itself. This is used to avoid overhead in applications that do expensive argument processing (e.g. creating strings) for probes. But this should be solvable so it would be possible to use perf-probe(1) on a std.h-enabled binary. Some distros already ship such binaries! Stefan -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>