Date: Thu, 24 May 2018 18:32:55 +0000 (UTC) From: Brooks Davis <brooks@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r334176 - head/lib/libc/sys Message-ID: <201805241832.w4OIWtNV032659@repo.freebsd.org>
next in thread | raw e-mail | index | archive | help
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.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201805241832.w4OIWtNV032659>