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# IRC, freenode, #hurd, 2013-01-18

    <braunr> youpi: what would you think of adding a debug-related syscall to
      gnumach so that we have a printf-like tool even in situations where the
      code can't perform an rpc (i.e. glibc)
    <youpi> could be useful indeed
    <youpi> I've found myself having a hard time making some printfs from odd
      places of glibc :)
    <braunr> i also suggest we make it unprivileged
    <youpi> not enabled by default then
    <youpi> otherwise it's an easy DoS
    <braunr> well, for now, we don't care much about DoS, but we do care about
      debugging
    <braunr> at least until the very core issues we have are understood and
      resolved
    <youpi> I usually frown on debugging feature being too open
    <braunr> me too
    <youpi> you would always forget dropping one
    <braunr> that's why i didn't suggest it earlier
    <braunr> but i'm wasting too much time finding other decently effective
      ways


## IRC, freenode, #hurd, 2013-01-19

    <braunr> youpi: how about we build this debugging system call in debugging
      versions only ?
    <braunr> i suppose you already use such versions for buildds anyway
    <braunr> MACH_DEBUG is always enabled
    <braunr> the debugging version only adds --enable-kdb if i'm right
    <pinotree> check debian/rules
    <braunr> that, and -fno-omit-frame-pointer


## IRC, freenode, #hurd, 2013-01-21

    <braunr> youpi: concerning gnumach, i've added a mach_print system call,
      with one argument (a null terminated string) to -dbg kernels
      (--enable-kbd)
    <youpi> k
    <braunr> if it's fine with you, i'll commit it too
    <youpi> I'm fine


## IRC, freenode, #hurd, 2013-04-07

    <braunr> see http://www.sceen.net/~rbraun/mach_print/ for an example to use
      it

[[Makefile]], [[mach_print.S]], [[main.c]].


## IRC, freenode, #hurd, 2013-07-01

    <youpi> braunr: btw, we are missing the symbol in mach/Versions
    <braunr> youpi: what symbol ?
    <youpi> so the libc-provided RPC stub is not available
    <youpi> mach_printf
    <youpi> -f
    <braunr> it's a system calll
    <braunr> not exported
    <youpi> s/RPC/system call/
    <braunr> that's expected
    <youpi> libc does provide stubs for system calls too
    <braunr> yes but not for this one
    <youpi> I don't see why we wouldn't want to include it
    <youpi> ?! it does
    <braunr> it's temporary
    <braunr> oh
    <braunr> there must be automatic parsing during build
    <youpi> sure
    <braunr> nice

    <braunr> youpi: if we're going to make this system call exported by glibc,
      i should change its interface first
    <braunr> it was meant as a very quick-and-dirty hack and directly accesses
      the caller's address space without going through a special copy-from-user
      function
    <braunr> not very portable


## IRC, freenode, #hurd, 2013-11-25

    <teythoon> can we get the mach_printf function somewhere so that it's
      easier to use please ?
    <braunr> well
    <braunr> i'm not comfortable with that
    <teythoon> y not ?
    <braunr> i don't consider mach_print being part of the interface yet
    <teythoon> ...
    <braunr> it's really a debugging call
    <braunr> not always available
    <teythoon> so what, let it fail if it is not
    <braunr> ok
    <braunr> i should change it first
    <braunr> pass a size argument
    <braunr> and do a proper copyin
    <teythoon> cool, thanks :)
    <braunr> then we could add that printf function in libshouldbeinlibc i
      guess
    <teythoon> that'd be nice, yes
    <braunr> hm
    <braunr> that would make only hurd servers able to use it though
    <braunr> unless we preload it
    <teythoon> well, i thought it's a staging area for libc ?
    <braunr> in theory yes, in practice some functions have been stuck there
      for ages
    <braunr> we'll discuss that with youpi and tschwinge 
    <braunr> and pinotree