man.postnix Miscellaneous man pages of Plan 9 related material

     BRK(2)                                                     BRK(2)

     NAME
          brk, sbrk - change memory allocation

     SYNOPSIS
          #include <u.h>
          #include <libc.h>

          int   brk(void *addr)

          void* sbrk(ulong incr)

     DESCRIPTION
          Brk sets the system's idea of the lowest bss location not
          used by the program (called the break) to addr rounded up to
          the next multiple of 8 bytes.  Locations not less than addr
          and below the stack pointer may cause a memory violation if
          accessed.

          In the alternate function sbrk, incr more bytes are added to
          the program's data space and a pointer to the start of the
          new area is returned.  Rounding occurs as with brk.

          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 brk. A call to sbrk with a zero argu-
          ment returns the lowest address in the dynamic segment.

     SOURCE
          /sys/src/libc/9sys/sbrk.c

     SEE ALSO
          intro(2), malloc(2), segattach(2), segbrk(2)

     DIAGNOSTICS
          These functions set errstr.

          The error return from sbrk is (void*)-1.

     Page 1                       Plan 9            (printed 10/29/25)