[Fwd: dlopen regression in 1.7? (or is it just me?)]

[Corinna Vinschen <corinna-cygwin at cygwin dot com>]

Hi Dave,

did you see this very fresh mail on the Cygwin list?
http://cygwin.com/ml/cygwin/2009-08/msg00352.html

----- Forwarded message from Peter Rosin -----
> Date: Tue, 11 Aug 2009 18:57:36 +0200
> From: Peter Rosin <schubidu>
> Subject: dlopen regression in 1.7? (or is it just me?)
> To: cygwin ML
> 
> Hi!
>
> I trouble with dlopen in cygwin-1.7
>
> STC:
> [...]
> $ ./reload
> one 0x63d80000, two 0x6ffc0000
> one 0x0, two 0x6ffc0000
----- End forwarded message -----

I debugged this a bit to find out what happens.  I don't understand
exactly what's going on, but the reason for the failing dlopen is a
crash in _cygwin_crt0_common, line 124.  That's the first of the
CONDITIONALLY_OVERRIDE macros.  When I link the simple1.dll and
simple2.dll files against a debug version of libcygwin.a (otherwise you
don't see the line number information) it crashes at this point with a
SIGSEGV.  Examining newu, it turns out that the cxx_malloc member points
into an address space not yet allocated:

(gdb) p newu
$1 = (per_process *) 0x6116b2c0
(gdb) p *newu
$2 = {initial_sp = 0x22ff68 "\210ÿ\"", magic_biscuit = 168, dll_major = 1007,
  dll_minor = 0, impure_ptr_ptr = 0x6116fcc0, envptr = 0x404028,
  malloc = 0x4015c0 <malloc>, free = 0x4015c8 <free>,
  realloc = 0x4015d0 <realloc>, fmode_ptr = 0x40402c, main = 0x4010f0 <main>,
  ctors = 0x401610, dtors = 0x40161c, data_start = 0x402000,
  data_end = 0x4020ac, bss_start = 0x404000, bss_end = 0x404050,
  calloc = 0x4015d8 <calloc>, premain = {0x401580 <cygwin_premain0>,
    0x401590 <cygwin_premain1>, 0x4015a0 <cygwin_premain2>,
    0x4015b0 <cygwin_premain3>}, run_ctors_p = 0, unused = {0, 0, 0, 0, 0, 0,
    0}, cxx_malloc = 0x67d42020, hmodule = 0x400000, api_major = 0,
  api_minor = 212, unused2 = {0, 0, 0, 0, 0, 0},
  threadinterface = 0x611f02a8, impure_ptr = 0x6116fce0}
(gdb) p *newu->cxx_malloc
Cannot access memory at address 0x67d42020
 
Since that only occurs on the second invocation of dlopen for the
same file, is it possible that there's some old information hanging
around?


Corinna

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