man(1) Manual page archive


NAME
     break, brk, sbrk - change core allocation

SYNOPSIS
     (break = 17.)
     sys break; addr

     char *brk(addr)

     char *sbrk(incr)

DESCRIPTION
     Break sets the system's idea of the lowest location not used
     by the program (called the break) to addr (rounded up to the
     next multiple of 64 bytes).  Locations not less than addr
     and below the stack pointer are not in the address space and
     will thus cause a memory violation if accessed.

     From C, brk will set the break to addr.  The old break is
     returned.

     In the alternate entry sbrk, incr more bytes are added to
     the program's data space and a pointer to the start of the
     new area is returned.

     When a program begins execution via exec the break is set at
     the highest location defined by the program and data storage
     areas.  Ordinarily, therefore, only programs with growing
     data areas need to use break.

SEE ALSO
     exec (II), alloc (III), end (III)

DIAGNOSTICS
     The c-bit is set if the program requests more memory than
     the system limit or if more than 8 segmentation registers
     would be required to implement the break.  From C, -1 is
     returned for these errors.

BUGS
     Setting the break in the range 0177700 to 0177777 is the
     same as setting it to zero.

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