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# Strategies
* [[GDB]] -- the GNU debugger
* [[gdb/Backtrace]]s
* [[subhurd]] -- running another Hurd system in parallel
* In context of [[glibc/debugging/ld_so_console]]: [[!message-id
"20111108190129.750BC2C098@topped-with-meat.com"]]
* [[rpctrace]] -- tracing [[RPC]]s
* [[microkernel/mach/gnumach/interface/syscall/mach_print]] sycall
# About Specific Packages
* [[glibc]]
* [[translator]]s
* [[trap_in_the_kernel]]
* [[hardware_watchpoint]]
# IRC, freenode, #hurd, 2013-06-30
<hacklu> braunr: I don't understand your question totally, but I want to
know how do you do this inspecting? <braunr> i have a small test program
that creates a thread, and inspect its state before any thread dies
<braunr> i use portinfo
<braunr> and rpctrace
<braunr> (there is also vminfo but you're not likely to need it for what
you're doing right now)
<hacklu> I have used rpctrace before, but portinfo, I will try it.
<hacklu> is portinfo show a process's all port use log?
<braunr> not log
<braunr> current state
<hacklu> dump the port name space?
<braunr> yes
<hacklu> I found some names are not continuous. how this come out?
<braunr> continuous ?
<hacklu> 101:send 103:send
<hacklu> missing 102
<braunr> some are freed
<braunr> a lot actually
<braunr> every RPC needs a reply port
<braunr> a temporary receive right to get replies from servers
<hacklu> so we can reuse the name which are freed before
<braunr> of course
## IRC, freenode, #hurd, 2013-11-08
<teythoon> braunr: btw, portinfo --search turned out quite nice for
detecting port leaks
<braunr> teythoon: something you added i guess ?
<teythoon> braunr: just yesterday
<teythoon> braunr: portinfo.c is full of useful ideas
<teythoon> braunr: for example, with a little help of the target server
(introspection protocol for libports) we could reliably detect leaks of
ports managed with libports
<braunr> yes introspection is probably required
## IRC, freenode, #hurd, 2013-11-20
<braunr> looking forward to using portinfo --search btw :)
<teythoon> yeah, that turned out to be quite helpful
<teythoon> that reminds me of the libports introspection idea :)
<braunr> introspection ?
<braunr> i mean
<braunr> that much, or a simple name for each port ?
<teythoon> I thought about returning more information, like the port class
<braunr> class ?
<braunr> i don't think you should
<braunr> iirc, classes are deemed not very useful for hurdng
<braunr> they were supposed to be removed, leaving only buckets
<teythoon> hurdng ... ?
<braunr> which seems more appropriate
<braunr> oh :)
<teythoon> well, no need for an introspectino interface then
<braunr> http://www.gnu.org/software/hurd/hurd/ng.html
<braunr> introspection is a bit too much
<teythoon> just look at the ports in the only port set then
<braunr> but something that would be reusable in lsof
<braunr> or /proc/*/maps
<braunr> would be very nice
<teythoon> if you could just be a little more specific then I might just go
and implement it ;)
<antrik> braunr: I don't think bucket information would be useful to the
outside world; classes OTOH might
<teythoon> worked fine with the mtab translator, let's do that again ;)
<braunr> antrik: buckets aren't, clearly
<braunr> antrik: more than classes, object types
<braunr> teythoon: well cat /proc/self/maps on linux
<antrik> ain't that the same? ;-)
<braunr> i don't know
<braunr> and i'm not sure it's that easy to make classes/types something
global
<braunr> so simply returning a path, or even more generally a description
string (sometimes a path)
<braunr> should be fine
<braunr> teythoon: just consider ports are frontends to objects
<teythoon> yes
<braunr> what i'd like is something like object.toString() :p
<teythoon> right
<braunr> something that would help us gather information about objects
accessible from user applications
<braunr> what is known as open files on unix :)
<teythoon> so 1) get a list of ports managed by libports, and 2) map those
ports to strings describing the object ?
<braunr> the list isn't strictly necessary
<braunr> just associate a string description to ports
<braunr> portinfo and such already create port lists
<teythoon> and fail if the port wasn't vaild?
<teythoon> rihgt
<braunr> well
<braunr> if the port isn't valid, you can't succeed anyway
<braunr> but
<braunr> what is more likely is the port not supporting the operation
<teythoon> yes
<braunr> in which case assume the empty string
<braunr> it may not be that straightforward
<braunr> imagine reply ports in select() for example
<teythoon> so where would I put such an rpc ?
<braunr> i'm not sure
<braunr> for a time, i considered making it a kernel call
<braunr> it could be implemented in the signal thread too
<teythoon> uh, oh, that's glibc land, right... ?
<braunr> in addition to "what are you waiting on", we could have "what's
the name for that port"
<braunr> yes
<braunr> :)
<braunr> well not name
<braunr> port names refer to integers
<braunr> port desc
<teythoon> yes
<braunr> i'm not sure how it should be done
<braunr> ideally, user applications should never have any reply ports
<braunr> and we could implement it all in libports
<braunr> select (and maybe others) make it hard
<teythoon> how so ?
<braunr> such calls don't expect any kind of request
<braunr> other than what's intended
<braunr> if select gets something else than a select reply, it returns with
an error
<teythoon> so ?
<braunr> changing that to deal with unexpected requests makes the select
implementation even harder than it is
<braunr> hum so, you don't want something like a mail server to fail
because you used lsof right ?
<teythoon> why would it get unexpected requests ?
<teythoon> no
<braunr> a new rpc like "give me your description" would be unexpected for
select
<braunr> servers properly demuxing messages would already reply they don't
implement the interface
<braunr> select would return an error to its caller
<braunr> that's very different
<teythoon> ah, well, ok, but if we put it in the signal thread, then lsof
would talk to that port
<braunr> yes
<teythoon> you mentioned that as a reason not to put it in libports ?
<braunr> yes
<braunr> normal applications don't use libports
<braunr> but they do have receive rights
<teythoon> I see, yes
## IRC, freenode, #hurd, 2013-11-29
<braunr> is the format of portinfo --search ORIG_PID => ... FOUND_PID =>
... ?
<teythoon> i think so, not sure atm
<braunr> 4 -> 5: 1 => 1: send (refs: 65534)
<braunr> :/
<braunr> hm i don't see such a right in pid 1
<teythoon> no, frompid -> topid: port name in frompid => corresponding name
in topid
<braunr> oh ok
# IRC, freenode, #hurd, 2013-11-08
[[!tag open_issue_gdb]]
<braunr> what i'd like personally would be gdb to be able to track threads
across address spaces, when it has the right to do so
<crocket> braunr, can gdb debug across threads?
<braunr> no
<braunr> the same is it can't follow system calls
<braunr> it can follow RPCs
<crocket> Then, I guess you have to debug multiple applications at once.
<braunr> can't*
<braunr> well
<braunr> the goal would be that
<braunr> right now, we debug them one at a time
<braunr> following our leads across applications
<braunr> it's a bit more tricky but not that hard
<teythoon> braunr: that would be nice indeed
<braunr> we're talking about cross-address-space debugging
<braunr> which is needed only when objects are shared between multiple
applications
<crocket> gdb can't do it
<braunr> but it can't do it on a monolithic system either
<braunr> people debug the kernel separately
<braunr> we debug our servers separately
<braunr> it's almost the same
<braunr> we don't debug all our servers, only those relevant in the code
path
<braunr> that's only a few
<teythoon> no it's worse for the monolithic kernel
<crocket> braunr, "Additionally, just tracking down a FS/write issue means
examining the user space process, the block device service, VFS service,
file system service and (possibly) the PCI service. If you get a blank on
that, its time to look at the IPC service. This is often easier in a
monolithic kernel."
<braunr> teythoon: depends
<braunr> crocket: agreed
<braunr> but again, such bugs are huge
<braunr> rare
<braunr> the only real class of cross-address-space bugs are leaks
<braunr> and leaks are easy to solve in practice
# [[open_issues/Translate_FD_or_Port_to_File_Name]]
# IRC, freenode, #hurd, 2014-01-30
<pere> btw, is there some alternative to strace? wanted to figure out why
lightdm didn't find dbus.
<pochu> there's rpctrace but that's a bit different
<youpi> there's also sotruss from recent glibc