mirror of https://github.com/mkerrisk/man-pages
111 lines
3.2 KiB
Groff
111 lines
3.2 KiB
Groff
.\" Copyright (c) 2008, Linux Foundation, written by by Michael Kerrisk
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.\" <mtk.manpages@gmail.com>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" License.
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.\"
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.TH END 3 2008-07-17 "GNU" "Linux Programmer's Manual"
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.SH NAME
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etext, edata, end \- end of program segments
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.SH SYNOPSIS
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.nf
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.BI extern " etext" ;
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.BI extern " edata" ;
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.BI extern " end" ;
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.fi
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.SH DESCRIPTION
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The addresses of these symbols indicate the end of various program
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segments:
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.TP
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.I etext
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This is the first address past the end of the text segment
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(the program code).
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.TP
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.I edata
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This is the first address past the end of the
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initialized data segment.
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.TP
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.I end
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This is the first address past the end of the
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uninitialized data segment (also known as the BSS segment).
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.SH CONFORMING TO
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Although these symbols have long been provided on most Unix systems,
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they are not standardized; use with caution.
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.SH NOTES
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The program must explicitly declare these symbols;
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they are not defined in any header file.
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On some systems the names of these symbols are preceded by underscores,
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thus:
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.IR _etext ,
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.IR _edata ,
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and
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.IR _end .
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These symbols are also defined for programs compiled on Linux.
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At the start of program execution,
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the program break will be somewhere near
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.IR &end
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(perhaps at the start of the following page).
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However, the break will change as memory is allocated via
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.BR brk (2)
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or
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.BR malloc (3).
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Use
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.BR sbrk (2)
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with an argument of zero to find the current value of the program break.
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.SH EXAMPLE
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When run, the program below produces output such as the following:
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.in +4n
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.nf
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$ ./a.out
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First address past:
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program text (etext) 0x8048568
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initialized data (edata) 0x804a01c
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uninitialized data (end) 0x804a024
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.fi
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.in
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.nf
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#include <stdio.h>
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#include <stdlib.h>
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extern char etext, edata, end; /* The symbols must have some type,
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or "gcc -Wall" complains */
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int
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main(int argc, char *argv[])
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{
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printf("First address past:\\n");
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printf(" program text (etext) %10p\\n", &etext);
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printf(" initialized data (edata) %10p\\n", &edata);
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printf(" uninitialized data (end) %10p\\n", &end);
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exit(EXIT_SUCCESS);
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}
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.fi
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.SH "SEE ALSO"
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.BR objdump (1),
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.BR readelf (1),
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.BR sbrk (2),
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.BR elf (5)
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