BRK(2)                      Linux Programmer's Manual                     BRK(2)

       brk, sbrk - change data segment size

       #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:
                   || ((_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

       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.

       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.

       4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.

       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.

       execve(2), getrlimit(2), end(3), malloc(3)

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Linux                              2021-03-22                             BRK(2)