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From:	"Dave Korn" <dave DOT korn AT artimi DOT com>
To:	<cygwin AT cygwin DOT com>
Subject:	RE: Need information about data and bss segment address access in cygwin
Date:	Fri, 20 Jan 2006 11:23:49 -0000
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Sudhahar wrote:

> from parent process to child process. After trying to find where the
> data_start and data_end get the address of running process data and
> bss segment, I ended up with a declaration  of
> 
> extern char _data_start__, _data_end__, _bss_start__, _bss_end__; in
> file Winsup.h
> 
> There is no other place where _data_start__, _data_end__,
> _bss_start__, _bss_end__ are defined they act as external symbols for
> cygwin.
> 
> Can anyone through some light on where these variables are actually
> declared and how they get the running process segment addresses.

  They are generated by the linker.  Take a look at the linker script by
running "ld --verbose".

dk AT espanola /usr/build/src-binutils/bfd> ld --verbose  | grep _start
     to include this between __data_start__ and __data_end__, but that
    __data_start__ = . ;
    __bss_start__ = . ;
    ___crt_xc_start__ = . ;
    ___crt_xi_start__ = . ;
    ___crt_xl_start__ = . ;
    ___crt_xp_start__ = . ;
    ___crt_xt_start__ = . ;
    ___tls_start__ = . ;
dk AT espanola /usr/build/src-binutils/bfd> ld --verbose  | grep _end
     to include this between __data_start__ and __data_end__, but that
     ".data_cygwin_nocopy" and explictly include it after __data_end__. */
    __data_end__ = . ;
    __bss_end__ = . ;
    ___crt_xc_end__ = . ;
    ___crt_xi_end__ = . ;
    /* ___crt_xl_end__ is defined in the TLS Directory support code */
    ___crt_xp_end__ = . ;
    ___crt_xt_end__ = . ;
    ___tls_end__ = . ;
    PROVIDE ( _end = .);
     __end__ = .;
dk AT espanola /usr/build/src-binutils/bfd>


    cheers,
      DaveK
-- 
Can't think of a witty .sigline today....


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