Date: Thu, 12 Feb 2015 11:27:28 +0200
From: Konstantin Belousov <kostikbel@gmail.com>
To: Bryan Drewery <bdrewery@FreeBSD.org>
Cc: threads@freebsd.org, arch@freebsd.org
Subject: Re: Fixing dlopen("libpthread.so")
Message-ID: <20150212092728.GE34251@kib.kiev.ua>
In-Reply-To: <54DBF417.4050206@FreeBSD.org>
References: <20141226165337.GJ1754@kib.kiev.ua> <54DBF417.4050206@FreeBSD.org>
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On Wed, Feb 11, 2015 at 06:30:15PM -0600, Bryan Drewery wrote: > On 12/26/2014 10:53 AM, Konstantin Belousov wrote: > > [Long] > > Proposed patch does the following: > [...] > > It seems libthr.3 needs to be updated for the dlopen(3) support, to > remove some of r272070. Also note the ordering comment (which I know you > may not be ready to change yet). Thanks for noting, I forgot about the man page and about the text. See the patch at the end of the message. > As for the dlclose(3) refusing to work on libthr, I cannot find the > supporting code. Where is it? libthr is linked with -z nodelete linker flag. diff --git a/lib/libthr/libthr.3 b/lib/libthr/libthr.3 index 4b636ce..8108e2f 100644 --- a/lib/libthr/libthr.3 +++ b/lib/libthr/libthr.3 @@ -1,5 +1,5 @@ .\" Copyright (c) 2005 Robert N. M. Watson -.\" Copyright (c) 2014 The FreeBSD Foundation, Inc. +.\" Copyright (c) 2014,2015 The FreeBSD Foundation, Inc. .\" All rights reserved. .\" .\" Part of this documentation was written by @@ -29,7 +29,7 @@ .\" .\" $FreeBSD$ .\" -.Dd September 26, 2014 +.Dd February 12, 2015 .Dt LIBTHR 3 .Os .Sh NAME @@ -200,45 +200,25 @@ Bigger values reduce the frequency of the FIFO discipline. The value must be between 0 and 255. .El .Sh INTERACTION WITH RUN-TIME LINKER -The +On load, .Nm -library must appear before -.Li libc -in the global order of depended objects. -.Pp -Loading -.Nm -with the -.Xr dlopen 3 -call in the process after the program binary is activated -is not supported, and causes miscellaneous and hard-to-diagnose misbehaviour. -This is due to -.Nm -interposing several important -.Li libc -symbols to provide thread-safe services. -In particular, -.Dv errno -and the locking stubs from -.Li libc -are affected. -This requirement is currently not enforced. -.Pp -If the program loads any modules at run-time, and those modules may require -threading services, the main program binary must be linked with -.Li libpthread , -even if it does not require any services from the library. +installs interposing handlers into the hooks exported by +.Li libc . +The interposers provide real locking implementation instead of the +stubs for single-threaded processes in +.Li , +cancellation support and some modifications to the signal operations. .Pp .Nm cannot be unloaded; the .Xr dlclose 3 function does not perform any action when called with a handle for .Nm . -One of the reasons is that the interposing of +One of the reasons is that the internal interposing of .Li libc functions cannot be undone. .Sh SIGNALS -The implementation also interposes the user-installed +The implementation interposes the user-installed .Xr signal 3 handlers. This interposing is done to postpone signal delivery to threads which
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