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From:	Heiko Elger <heiko_elger AT arburg DOT com>
Subject:	Re: perl fork error: =?utf-8?b?Y2hpbGRfaW5mb19mb3JrOjphYm9ydDo=?= data segment start: - example code!
Date:	Thu, 9 Feb 2012 14:50:18 +0000 (UTC)
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Corinna Vinschen writes:

> So with the latest snapshot we can at least see which DLL is affected
> by this problem.  Then we can check where this DLL is really supposed to
> be in memory (objdump -h) and then we can check what really is at this
> location in the process VM (/proc/$PID/maps)

Hello, 

I instrumented dll_list::alloc() a little bit - a now we will see the 
following.
New code from Corinna and some other code ...

$ ./forktest.pl
start
      0 [main] perl 8424 dll_list::alloc: alloc() - Error
    396 [main] perl 8424 dll_list::alloc: 
C:\PROGRAMME\CYGWIN1710MINIMAL\bin\cygperl5_10.dll: Loaded to different 
address: parent(0xC40000) != child(0xB80000)
   1116 [main] perl 8424 dll_list::alloc: data segment start: parent
(0xD7A000) != child(0xCBA000)
   1240 [main] perl 8424 dll_list::alloc: data segment end: parent(0xD991E0) !
= child(0xCD91E0)
   1350 [main] perl 8424 dll_list::alloc: bss segment start: parent(0xD9C000) !
= child(0xCDC000)
   1461 [main] perl 8424 dll_list::alloc: bss segment end: parent(0xD9C610) != 
child(0xCDC610)
   1538 [main] perl 8424 dll_list::alloc: Long Sleep: 1h
   1599 [main] perl 8424 dll_list::alloc: Sleep 100s

With sysinternal tool vmmap I see the correct addresses of cygperl5_10.dll of 
the parent perl process (BSS and DATA)
Using vmmap for the forked perl process is not possible - utility hangs - 
perhaps cause of hanging process?!?
Similar problem looking into /proc/PID/map ....

Why is this wrong mapping done?
I figured our the following:

Using SEP there is a service running called sysplant ("Application and Device 
Control", system32\Drivers\SysPlant.sys).
Disabling this service on cmd line (cmd.exe) 
    sc config sysplant start= disabled
rebooting all seems to work fine!

I will contact Symantec for more details about this service.

The output of objdump -h is the following:
$ objdump -h cygperl5_10.dll

cygperl5_10.dll:     file format pei-i386

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .text         001386fc  57011000  57011000  00000400  2**4
                  CONTENTS, ALLOC, LOAD, READONLY, CODE, DATA
  1 .data         0001f1e4  5714a000  5714a000  00138c00  2**5
                  CONTENTS, ALLOC, LOAD, DATA
  2 .rdata        00000780  5716a000  5716a000  00157e00  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  3 .eh_frame     00000004  5716b000  5716b000  00158600  2**2
                  CONTENTS, ALLOC, LOAD, DATA
  4 .bss          00000610  5716c000  5716c000  00000000  2**5
                  ALLOC
  5 .edata        0000dcd0  5716d000  5716d000  00158800  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  6 .idata        00001a08  5717b000  5717b000  00166600  2**2
                  CONTENTS, ALLOC, LOAD, DATA
  7 .reloc        00008818  5717d000  5717d000  00168200  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  8 .gnu_debuglink 00000014  57186000  57186000  00170c00  2**2
                  CONTENTS, READONLY

What is the recommended address layout?
Should DATA be mapped to 0x5714a000 and BSS to 0x5716c000?

Well - I just do the test again with disabled Symantec sysplant service.

... and ... voila ...
Verifying address layout is:
cygperl5_10.dll is loaded at address 0x50710000 and all addresses shown with 
objdump -h
are used!

That's really fine ...

Thanks a lot Corinna and all others ....

best regards

Heiko



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