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If applicable, add the following below this CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your own identifying information: Portions Copyright [yyyy] [name of copyright owner] .TH brk 2 "14 Jan 1997" "SunOS 5.11" "System Calls" .SH NAME brk, sbrk \- change the amount of space allocated for the calling process's data segment .SH SYNOPSIS .LP .nf #include \fBint\fR \fBbrk\fR(\fBvoid *\fR\fIendds\fR); .fi .LP .nf \fBvoid *\fR\fBsbrk\fR(\fBintptr_t\fR \fIincr\fR); .fi .SH DESCRIPTION .sp .LP The \fBbrk()\fR and \fBsbrk()\fR functions are used to change dynamically the amount of space allocated for the calling process's data segment (see \fBexec\fR(2)). The change is made by resetting the process's break value and allocating the appropriate amount of space. The break value is the address of the first location beyond the end of the data segment. The amount of allocated space increases as the break value increases. Newly allocated space is set to zero. If, however, the same memory space is reallocated to the same process its contents are undefined. .sp .LP When a program begins execution using \fBexecve()\fR the break is set at the highest location defined by the program and data storage areas. .sp .LP The \fBgetrlimit\fR(2) function may be used to determine the maximum permissible size of the \fIdata\fR segment; it is not possible to set the break beyond the \fBrlim_max\fR value returned from a call to \fBgetrlimit()\fR, that is to say, "\fBend + rlim.rlim_max\fR." See \fBend\fR(3C). .sp .LP The \fBbrk()\fR function sets the break value to \fIendds\fR and changes the allocated space accordingly. .sp .LP The \fBsbrk()\fR function adds \fIincr\fR function bytes to the break value and changes the allocated space accordingly. The \fIincr\fR function can be negative, in which case the amount of allocated space is decreased. .SH RETURN VALUES .sp .LP Upon successful completion, \fBbrk()\fR returns \fB0\fR. Otherwise, it returns \fB\(mi1\fR and sets \fBerrno\fR to indicate the error. .sp .LP Upon successful completion, \fBsbrk()\fR returns the prior break value. Otherwise, it returns \fB(void *)\(mi1\fR and sets \fBerrno\fR to indicate the error. .SH ERRORS .sp .LP The \fBbrk()\fR and \fBsbrk()\fR functions will fail and no additional memory will be allocated if: .sp .ne 2 .mk .na \fB\fBENOMEM\fR\fR .ad .RS 10n .rt The data segment size limit as set by \fBsetrlimit()\fR (see \fBgetrlimit\fR(2)) would be exceeded; the maximum possible size of a data segment (compiled into the system) would be exceeded; insufficient space exists in the swap area to support the expansion; or the new break value would extend into an area of the address space defined by some previously established mapping (see \fBmmap\fR(2)). .RE .sp .ne 2 .mk .na \fB\fBEAGAIN\fR\fR .ad .RS 10n .rt Total amount of system memory available for private pages is temporarily insufficient. This may occur even though the space requested was less than the maximum data segment size (see \fBulimit\fR(2)). .RE .SH USAGE .sp .LP The behavior of \fBbrk()\fR and \fBsbrk()\fR is unspecified if an application also uses any other memory functions (such as \fBmalloc\fR(3C), \fBmmap\fR(2), \fBfree\fR(3C)). The \fBbrk()\fR and \fBsbrk()\fR functions have been used in specialized cases where no other memory allocation function provided the same capability. The use of \fBmmap\fR(2) is now preferred because it can be used portably with all other memory allocation functions and with any function that uses other allocation functions. .sp .LP It is unspecified whether the pointer returned by \fBsbrk()\fR is aligned suitably for any purpose. .SH ATTRIBUTES .sp .LP See \fBattributes\fR(5) for descriptions of the following attributes: .sp .sp .TS tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) . ATTRIBUTE TYPEATTRIBUTE VALUE _ MT-LevelMT-Safe .TE .SH SEE ALSO .sp .LP \fBexec\fR(2), \fBgetrlimit\fR(2), \fBmmap\fR(2), \fBshmop\fR(2), \fBulimit\fR(2), \fBend\fR(3C), \fBfree\fR(3C), \fBmalloc\fR(3C) .SH NOTES .sp .LP The value of \fIincr\fR may be adjusted by the system before setting the new break value. Upon successful completion, the implementation guarantees a minimum of \fIincr\fR bytes will be added to the data segment if \fIincr\fR is a positive value. If \fIincr\fR is a negative value, a maximum of \fIincr\fR bytes will be removed from the data segment. This adjustment may not be necessary for all machine architectures. .sp .LP The value of the arguments to both \fBbrk()\fR and \fBsbrk()\fR are rounded up for alignment with eight-byte boundaries. .SH BUGS .sp .LP Setting the break may fail due to a temporary lack of swap space. It is not possible to distinguish this from a failure caused by exceeding the maximum size of the data segment without consulting \fBgetrlimit()\fR.