Q43165: LINK: Creating and Accessing _edata and _end

Article: Q43165
Product(s): See article
Version(s): 3.X 4.06 | 5.01.20 5.01.21
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | s_c | mspl13_basic
Last Modified: 6-APR-1989

LINK creates the two symbols _edata and _end when the LINK option
/DOSSEG is used. If a program is compiled by a Microsoft high-level
language compiler, or if an assembly program written in Microsoft MASM
uses .DOSSEG directive, LINK uses this option automatically.

LINK gives _edata the address of the beginning of BSS segment and
gives _end the address of the end of BSS segment. Since the STACK
segment is directly above the BSS segment, the address of _end also
marks the lowest address of the STACK segment.

To obtain the addresses for these two symbols, declare the following
in your C program:

unsigned char edata, end ;

The addresses, &edata and &end, can now be used to locate _BSS and
STACK. They can also be examined in CodeView. Modifying these two
variables is not recommended.

Note: The segment BSS referred to in this article actually includes
the segment C_COMMON. However in a map file created by LINK, BSS and
C_COMMON are listed as two separate segments.

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