Date: Mon, 29 Aug 2016 22:10:35 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Andrey Chernov <ache@freebsd.org> Cc: John Baldwin <jhb@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r304928 - in head/lib/libc: amd64/sys i386/sys sys Message-ID: <20160829191035.GV83214@kib.kiev.ua> In-Reply-To: <a6921ce6-ca99-6ee9-24de-fe90a440879d@freebsd.org> References: <201608272303.u7RN3N0D078505@repo.freebsd.org> <1595604.93PBdSz0kX@ralph.baldwin.cx> <20160829065813.GP83214@kib.kiev.ua> <18206408.GMLM77D01s@ralph.baldwin.cx> <20160829180454.GU83214@kib.kiev.ua> <a6921ce6-ca99-6ee9-24de-fe90a440879d@freebsd.org>
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On Mon, Aug 29, 2016 at 09:16:29PM +0300, Andrey Chernov wrote: > Previous text is documented everywhere and describing usual good > practice, so it should remains in place, in that means r304928 should be > reverted, because replace proper way of doing things with obsoleted > feature description. > > What I suggest is not _replace_ old text with new, but _add_ new text as > describing current and not recommended way, with the direct mention that > this feature is obsoleted and not recommended for relay on it. > diff --git a/lib/libc/sys/ptrace.2 b/lib/libc/sys/ptrace.2 index 48802f4..d406efc 100644 --- a/lib/libc/sys/ptrace.2 +++ b/lib/libc/sys/ptrace.2 @@ -2,7 +2,7 @@ .\" $NetBSD: ptrace.2,v 1.2 1995/02/27 12:35:37 cgd Exp $ .\" .\" This file is in the public domain. -.Dd August 28, 2016 +.Dd August 29, 2016 .Dt PTRACE 2 .Os .Sh NAME @@ -900,19 +900,29 @@ argument is ignored. .Pp Additionally, other machine-specific requests can exist. .Sh RETURN VALUES +Most requests return 0 on success and \-1 on error. Some requests can cause .Fn ptrace to return \-1 -as a non-error value; to disambiguate, +as a non-error value, among them are +.Dv PT_READ_I +and +.Dv PT_READ_D , +which return the value read from the process memory on success. +To disambiguate, .Va errno -is set to 0 in the libc wrapper for the -.Fn ptrace -system call and +can be set to 0 before the call and checked afterwards. +.Pp +Current .Fn ptrace -callers can reliably check +implementation always sets +.Va errno +to 0 before calling into kernel, both for historic reasons and for +consistency with other operating systems. +It is recommended to assign zero to .Va errno -for non-zero value afterwards. +explicitely for future compatibility. .Sh ERRORS The .Fn ptrace
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