Date: Thu, 31 May 2018 16:01:10 +0000 (UTC) From: Brooks Davis <brooks@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-11@freebsd.org Subject: svn commit: r334439 - stable/11/lib/libc/sys Message-ID: <201805311601.w4VG1Adw067562@repo.freebsd.org>
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Author: brooks Date: Thu May 31 16:01:10 2018 New Revision: 334439 URL: https://svnweb.freebsd.org/changeset/base/334439 Log: MFC r334176: 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. Approved by: re (kib) Reviewed by: emaste, Marcin Cieślak Sponsored by: DARPA, AFRL Differential Revision: https://reviews.freebsd.org/D15535 Modified: stable/11/lib/libc/sys/brk.2 Directory Properties: stable/11/ (props changed) Modified: stable/11/lib/libc/sys/brk.2 ============================================================================== --- stable/11/lib/libc/sys/brk.2 Thu May 31 16:00:03 2018 (r334438) +++ stable/11/lib/libc/sys/brk.2 Thu May 31 16:01:10 2018 (r334439) @@ -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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