huschi.net

BRK(2)                     Linux Programmer's Manual                    BRK(2)
NAME
       brk, sbrk - change data segment size
SYNOPSIS
       #include <unistd.h>
       int brk(void *addr);
       void *sbrk(intptr_t increment);
   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
       brk(), sbrk():
           Since glibc 2.19:
               _DEFAULT_SOURCE ||
                   (_XOPEN_SOURCE >= 500) &&
                   ! (_POSIX_C_SOURCE >= 200112L)
           From glibc 2.12 to 2.19:
               _BSD_SOURCE || _SVID_SOURCE ||
                   (_XOPEN_SOURCE >= 500) &&
                   ! (_POSIX_C_SOURCE >= 200112L)
           Before glibc 2.12:
               _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500
DESCRIPTION
       brk()  and  sbrk()  change  the  location  of  the program break, which
       defines the end of the process's data segment (i.e., the program  break
       is the first location after the end of the uninitialized data segment).
       Increasing the program break has the effect of allocating memory to the
       process; decreasing the break deallocates memory.
       brk()  sets the end of the data segment to the value specified by addr,
       when that value is reasonable, the system has enough  memory,  and  the
       process does not exceed its maximum data size (see setrlimit(2)).
       sbrk() increments the program's data space by increment bytes.  Calling
       sbrk() with an increment of 0 can be used to find the current  location
       of the program break.
RETURN VALUE
       On success, brk() returns zero.  On error, -1 is returned, and errno is
       set to ENOMEM.
       On success, sbrk() returns the previous program break.  (If  the  break
       was  increased,  then this value is a pointer to the start of the newly
       allocated memory).  On error, (void *) -1 is returned, and errno is set
       to ENOMEM.
CONFORMING TO
       4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.
NOTES
       Avoid  using  brk() and sbrk(): the malloc(3) memory allocation package
       is the portable and comfortable way of allocating memory.
       Various systems use various types for the argument of  sbrk().   Common
       are int, ssize_t, ptrdiff_t, intptr_t.
   C library/kernel differences
       The  return value described above for brk() is the behavior provided by
       the glibc wrapper function for the Linux brk() system call.   (On  most
       other  implementations,  the  return value from brk() is the same; this
       return value was also specified in SUSv2.)  However, the  actual  Linux
       system  call returns the new program break on success.  On failure, the
       system call returns the current break.  The glibc wrapper function does
       some  work  (i.e.,  checks  whether the new break is less than addr) to
       provide the 0 and -1 return values described above.
       On Linux, sbrk() is implemented as a library  function  that  uses  the
       brk()  system  call,  and does some internal bookkeeping so that it can
       return the old break value.
SEE ALSO
       execve(2), getrlimit(2), end(3), malloc(3)
COLOPHON
       This page is part of release 4.15 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.
Linux                             2016-03-15                            BRK(2)