Messages in this thread | | | Subject | Re: malloc() tracing in perf? | From | Peter Zijlstra <> | Date | Thu, 06 Aug 2009 14:59:34 +0200 |
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On Thu, 2009-08-06 at 07:55 -0400, Frank Ch. Eigler wrote: > Hi - > > On Thu, Aug 06, 2009 at 01:28:14PM +0200, Peter Zijlstra wrote: > > [...] > > > That work is ongoing, and being discussed on utrace-devel@redhat.com, > > > since it is a prerequisite. > > > > Still hiding the discussion and the design never helped anybody. > > I guess "hiding" is a matter of opinion.
Yeah in plain sight where nobody looks, really I thought the idea was to get utrace upstream, this means posting to linux-kernel. Going on LKML posts I'd say the utrace project was dead. Same goes for uprobe.
I've told this before and I'll say it again, post to LKML.
> > > While these deliberations are ongoing, you can use systemtap. Probing > > > random places in userspace is about as casual as probing the kernel: > > > > Right, but that still doesn't tell us anything on how you're doing that, > > does it? > > Since you asked... the probe process("/lib64/libc.so.6") points > systemtap to a shared library file, whose symbol table & debug data > gives us information about what functions & parameters are available. > Among other things, we record a shared-library base-relative address > for the function. > > At run time, we monitor the entire system (or just a given process if > -x PID/-c CMD was specified) to see when that shared library gets > loaded. (This in turn is done with a utrace-based hook of the mmap > syscall - see "task_finder" in our sources).
Does this also iterate the already existing tasks to find if it was already mmap()ed?
> This overview skims over issues related to return probes, tracing > buffer manipulations, and much other stuff.
Right, so you basically read the (dwarf2) debug info for a particular lib/symbol and generate a kernel module that knows about that and then insert that into the kernel to act as a uprobe handler?
Uprobe will then do the code rewrite on mmap() time to insert a trap much like kprobe does? What if its a JITed code section and the JIT rewrites it? Will uprobes detect that?
> All the code for this is hidden in plain sight in every systemtap > release, so please feel free to refer to that and/or ask more detailed > questions.
I thought the goal was to get stuff upstream, but if you want to continue living in la-la land and not bother with upstream Linux then so be it I guess :-(
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