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Re: Regression for OCaml introduced by rebase 4.4.4




On Feb  8 11:47, David Allsopp wrote:
> TL;DR flexlink-compiled DLLs (i.e. ocaml libraries) are broken by the
> 0x200000000 base address requirement added in rebase 4.4.4. Possible fixes
> for this at the bottom.
> 
> Commit bfd383 in the rebase sources introduces a new minimum base address
> requirement of 0x200000000 for Cygwin64. This is a problem for the correct
> operation of the flexdll package and affects ocaml. On a fresh up-to-date
> Cygwin64 installation, install the ocaml package:
> 
>   $ rebase -i /usr/lib/ocaml/stublibs/*
>   /usr/lib/ocaml/stublibs/dllbigarray.so    base 0x000000010000 size
> 0x00015000 *
>   /usr/lib/ocaml/stublibs/dllcamlstr.so     base 0x000000010000 size
> 0x00014000 *
>   /usr/lib/ocaml/stublibs/dllgraphics.so    base 0x000000010000 size
> 0x00038000 *
> [...]
> Here you can see a problem we already know about with flexlink - all
> libraries have a base address of 0x10000
> (https://github.com/alainfrisch/flexdll/issues/50).
> 
> However, this allows you to load libraries dynamically:
> 
>   $ ocaml
>           OCaml version 4.04.2
> 
>   # #load "unix.cma";;
>   # #directory "+threads";;
>   # #load "threads.cma";;
> 
> but not fork (we know about this problem):
> 
>   # Unix.fork ();;
>         0 [main] ocamlrun 5688 child_info_fork::abort: address space needed
> by 'dllunix.so' (0x400000) is already occupied
>   Exception: Unix.Unix_error (Unix.EAGAIN, "fork", "").
> 
> Now do a rebaseall.
> 
>   $ rebase -i /usr/lib/ocaml/stublibs/*
>   /usr/lib/ocaml/stublibs/dllvmthreads.so   base 0x0003fec20000 size
> 0x0001f000
>   /usr/lib/ocaml/stublibs/dllunix.so        base 0x0003fec40000 size
> 0x0004c000
> [...]
> 
> So forking should now be fine. However:
> 
>   $ ocaml
>           OCaml version 4.04.2
> 
>   # #load "unix.cma";;
>   Cannot load required shared library dllunix.
>   Reason: /usr/lib/ocaml/stublibs/dllunix.so: flexdll error: cannot relocate
> RELOC_REL32, target is too far: 0xfffffffc013d8b5f  0x13d8b5f. 

The problem is this:  Given that the lib is in a safe space anyway,
why do you still try to relocate it?  That's exactly what you don't
have to do anymore and you shouldn't do this.  The DLL is loaded
where it belongs, end of story.  What should another relocation
gain?  So, just wwitch it off for 64 bit Cygwin, no?


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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