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.TH BRK 2
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.SH NAME
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brk, sbrk \- change memory allocation
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.SH SYNOPSIS
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.B #include <u.h>
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.br
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.B #include <libc.h>
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.PP
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.ta \w'\fLvoid* 'u
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.B
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int	brk(void *addr)
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.PP
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.B
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void*	sbrk(ulong incr)
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.SH DESCRIPTION
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.I Brk
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sets the system's idea of the lowest bss location not used by the program
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(called the break)
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to
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.I addr
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rounded up to the next multiple of 8 bytes.
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Locations not less than
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.I addr
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and below the stack pointer
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may cause a memory violation if accessed.
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.PP
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In the alternate function
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.IR sbrk ,
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.I incr
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more bytes are added to the
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program's data space and a pointer to the
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start of the new area is returned.
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Rounding occurs as with
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.IR brk .
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.PP
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When a program begins execution via
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.I exec
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the break is set at the
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highest location defined by the program
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and data storage areas.
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Ordinarily, therefore, only programs with growing
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data areas need to use
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.IR brk .
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A call to
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.I sbrk
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with a zero argument returns the lowest address
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in the dynamic segment.
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.SH SOURCE
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.B /sys/src/libc/9sys/sbrk.c
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.SH SEE ALSO
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.IR intro (2),
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.IR malloc (2),
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.IR segattach (2),
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.IR segbrk (2)
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.SH DIAGNOSTICS
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These functions set
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.IR errstr .
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.PP
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The error return from
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.I sbrk
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is
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.BR (void*)-1 .