svn commit: r334176 - head/lib/libc/sys
Brooks Davis
brooks at FreeBSD.org
Thu May 24 18:32:56 UTC 2018
Author: brooks
Date: Thu May 24 18:32:54 2018
New Revision: 334176
URL: https://svnweb.freebsd.org/changeset/base/334176
Log:
Indicate the brk/sbrk are deprecated and not portable.
More firmly suggest mmap(2) instead.
Include the history of arm64 and riscv shipping without brk/sbrk.
Mention that sbrk(0) produces unreliable results.
Reviewed by: emaste, Marcin Cieślak
MFC after: 3 days
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D15535
Modified:
head/lib/libc/sys/brk.2
Modified: head/lib/libc/sys/brk.2
==============================================================================
--- head/lib/libc/sys/brk.2 Thu May 24 18:22:13 2018 (r334175)
+++ head/lib/libc/sys/brk.2 Thu May 24 18:32:54 2018 (r334176)
@@ -28,7 +28,7 @@
.\" @(#)brk.2 8.4 (Berkeley) 5/1/95
.\" $FreeBSD$
.\"
-.Dd December 15, 2015
+.Dd May 24, 2018
.Dt BRK 2
.Os
.Sh NAME
@@ -51,6 +51,10 @@ and
.Fn sbrk
functions are legacy interfaces from before the
advent of modern virtual memory management.
+They are deprecated and not present on the arm64 or riscv architectures.
+The
+.Xr mmap 2
+interface should be used to allocate pages instead.
.Ef
.Pp
The
@@ -152,6 +156,11 @@ The
.Fn brk
function appeared in
.At v7 .
+.Fx 11.0
+introduced the arm64 and riscv architectures which do not support
+.Fn brk
+or
+.Fn sbrk .
.Sh BUGS
Mixing
.Fn brk
@@ -168,3 +177,9 @@ It is not possible to distinguish this
from a failure caused by exceeding the maximum size of
the data segment without consulting
.Xr getrlimit 2 .
+.Pp
+.Fn sbrk
+is sometimes used to monitor heap use by calling with an argument of 0.
+The result is unlikely to reflect actual utilization in combination with an
+.Xr mmap 2
+based malloc.
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