Re: [BProc] Access to /proc/<pid>/exe

[William H. <wd...@sg...>]

On Fri, 12 Dec 2003 er...@he... wrote:

> Bingo.  That's it exactly.  The 'readlink' for that one looks through
> the process's memory to find a region tagged as 'VM_EXECUTABLE' and
> tells you what file that one is mapped from.
> 
> I haven't done anything to try and make it so I guess it shouldn't. It
> probably wouldn't be that hard to make it do something reasonable if you
> really wanted it to work.  It might get a little weird if remote
> processes exec something that doesn't exist on the front end though.

Thanks for the response Erik!

Actually, how badly I wanted this to work may depend on the answer to 
my next question... How much of the ptrace interface is supported? 

I know from your paper at:

     http://public.lanl.gov/cluster/papers/papers/hendriks-ics02.pdf

that at least partial support is provided. And some of the text in this
paper implies that one can, at the very least, peek and poke the remote
process' address space via the ghost. Is that correct?

I'm currently trying to get Dyninst (http://www.dyninst.org/) working on
a bproc cluster. My goal is run a tool implemented using Dyninst on the 
master node while manipulating processes on the slave nodes. The first 
problem I encountered was the issue with /proc/<pid>/exe. This was easy 
enough to work around for the moment. But now I'm running into a Dyninst 
error message:

DYNINST ERROR: System error: <>unable to read 256@0x080483C0 from process 
data space: No such process (pid=4715)
EXIT DYNINST ERROR: Internal error: unable to find addr of _dl_open

Where pid 4715 is the ghost process for the real process I'm trying to
manipulate. I realize, of course, that you are not necessarily familiar
with Dyninst.  I've dug through their source and the error message leads
me to believe that a call to ptrace(PTRACE_PEEKTEXT, 4715, ...) failed.

Should performing a PTRACE_PEEKTEXT on a remote process work properly? Any 
caveats involved in doing so? How about the other PTRACE operations? 
Should they all work? Or just a specific subset?

Thanks again, Erik, for your time and patience with my questions!

-------------------------------------------------------------------
William Hachfeld                                EMail: wd...@sg...
SGI Debugger, Object, and Performance Tools     Phone: 651-683-3103