_end, _etext, or _edata Identifier
Purpose
Define the first addresses following the program, initialized data, and all data.
Syntax
extern _end;extern _etext;extern _edata;Description
The external names _end, _etext, and _edata are defined by the loader for all programs. They are not subroutines but identifiers associated with the following addresses:
| Item | Description |
|---|---|
| _etext | The first address following the program text. |
| _edata | The first address following the initialized data region. |
| _end | The first address following the data region that is not initialized. The name end (with no underscore) defines the same address as does _end (with underscore). |
The break value of the program is the first location beyond the data. When a program begins running, this location coincides with end. However, many factors can change the break value, including:
- The brk or sbrk subroutine
- The malloc subroutine
- The standard I/O subroutines
- The -p flag with the cc command
Therefore, use the brk or sbrk(0) subroutine, not the end address, to determine the break value of the program.