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[[!tag open_issue_glibc open_issue_gnumach]]


# IRC, frenode, #hurd, 2012-11-04

    <tschwinge> braunr, pinotree, youpi: Has either of you already figured out
      what [glibc]/sysdeps/mach/hurd/dl-sysdep.c:fmh »XXX loser kludge for
      vm_map kernel bug« is about?
    <pinotree> tschwinge: ETOOLOWLEVELFORME :)
    <pinotree> tschwinge: 5bf62f2d3a8af353fac661b224fc1604d4de51ea added it
    <braunr> tschwinge: no, but that looks interesting
    <braunr> i'll have a look later
    <tschwinge> Heh, "interesting".  ;-)
    <tschwinge> It seems related to vm_map's mask
      parameter/ELF_MACHINE_USER_ADDRESS_MASK, though the latter in only used
      in the mmap implementation in sysdeps/mach/hurd/dl-sysdep.c (in mmap.c, 0
      is passed; perhaps due to the bug?).
    <tschwinge> braunr: Anyway, I'd already welcome a patch to simply turn that
      into a more comprehensible form.
    <braunr> tschwinge: ELF_MACHINE_USER_ADDRESS_MASK is defined as "Mask
      identifying addresses reserved for the user program, where the dynamic
      linker should not map anything."
    <braunr> about the vm_map parameter, which is a mask, it is described by
      "Bits asserted in this mask must not be asserted in the address returned"
    <braunr> so it's an alignment constraint
    <braunr> the kludge disables alignment, apparently because gnumach doesn't
      handle them correctly for some cases
    <tschwinge> braunr: But ELF_MACHINE_USER_ADDRESS_MASK is 0xf8000000, so I'd
      rather assume this means to restrict to addresses lower than 0xf8000000.
      (What are whigher ones reserved for?)
    <braunr> tschwinge: the linker i suppose
    <braunr> tschwinge: sorry, i don't understand what
      ELF_MACHINE_USER_ADDRESS_MASK really is used for :/
    <braunr> tschwinge: it looks unused for the other systems
    <braunr> tschwinge: i guess it's just one way to partition the address
      space, so that the linker knows where to load libraries and mmap can
      still allocate large contiguous blocks
    <braunr> tschwinge: 0xf8000000 means each "chunk" of linker/other blocks
      are 128 MiB large
    <tschwinge> braunr: OK, thanks for looking.  I guess I'll ask Roland about
      it.
    <braunr> it could be that gnumach isn't good at aligning to large values

[[!message-id "87fw4pb4c7.fsf@kepler.schwinge.homeip.net"]]


# IRC, frenode, #hurd, 2013-01-22

In context of [[libpthread]].

    <braunr> pinotree: do you understand what the fmh function does in
      sysdeps/mach/hurd/dl-sysdep.c ?
    <braunr> ok i understand what it does
    <braunr> and youpi has changed the code, so he does too
    <braunr> youpi: do you have a suggestion about how to solve this issue in
      the fmh function ?
    <youpi> do we remember which bug it's after?
    <braunr> what do you mean ?
    <braunr> ah
    <braunr> no :/
    <braunr> it could be a good occasion to get rid of it, yes