Blob Blame Raw
#
# Posted upstream:
# https://sourceware.org/ml/libc-alpha/2013-10/msg00065.html
#
# This is related to bug 1013801 in that it fixes the problem
# by modifying the runtime. In bug 1013801 we have libselinux
# using pthread_atfork which pulls in libpthread, but we don't
# want that, we want libpthread to be pulled in only when
# actually needed by the application. This patch makes it
# possible to avoid requiring libpthread and still use
# pthread_atfork.
#
# The general idea for the design is in the leading comment
# in the source code.
#
Index: glibc-2.24-163-ge299076/nptl/Makefile
===================================================================
--- glibc-2.24-163-ge299076.orig/nptl/Makefile
+++ glibc-2.24-163-ge299076/nptl/Makefile
@@ -30,7 +30,8 @@ install-lib-ldscripts := libpthread.so
 
 routines = alloca_cutoff forward libc-lowlevellock libc-cancellation \
 	   libc-cleanup libc_pthread_init libc_multiple_threads \
-	   register-atfork unregister-atfork
+	   register-atfork unregister-atfork libc_pthread_atfork
+static-only-routines += libc_pthread_atfork
 shared-only-routines = forward
 
 # We need to provide certain routines for compatibility with existing
Index: glibc-2.24-163-ge299076/nptl/libc_pthread_atfork.c
===================================================================
--- /dev/null
+++ glibc-2.24-163-ge299076/nptl/libc_pthread_atfork.c
@@ -0,0 +1,54 @@
+/* Copyright (C) 2013 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* The standard design pattern for making it optional to link against
+   libpthread is to mark the function weak, test if the function
+   address is non-zero and call the function, otherwise use a fallback.
+   The problem with pthread_atfork is that there is no viable
+   fallback.  If you need to do something during fork it has to be done
+   via pthread_atfork.  This makes having libpthread optional and using
+   pthread_atfork impossible.  We make it possible by providing
+   pthread_atfork in libc_nonshared.a.  The real work of pthread_atfork
+   is done by __register_atfork which is already provided in
+   libc_nonshared.a.  It's included in libc_nonshared.a because
+   __dso_handle has to be unique to each DSO such that unloading the DSO
+   can unregister the atfork handlers.  We build pthread_atfork again
+   under a different file name and include it into libc_nonshared.a and
+   libc.a. We keep pthread_atfork in libpthread_nonshared.a and
+   libpthread.a for compatibility and completeness.
+
+   Applications that can't rely on a new glibc should use the following
+   code to optionally include libpthread and still register a function
+   via pthread_atfork i.e. use __register_atfork directly:
+
+   extern void *__dso_handle __attribute__ ((__weak__, __visibility__ ("hidden")));
+   extern int __register_atfork (void (*) (void), void (*) (void), void (*) (void), void *);
+
+   static int __app_atfork (void (*prepare) (void), void (*parent) (void), void (*child) (void))
+     {
+       return __register_atfork (prepare, parent, child,
+				 &__dso_handle == NULL ? NULL : __dso_handle);
+     }
+
+   This code requires glibc 2.3.2 or newer. Previous to 2.3.2 no such
+   interfaces exist and at that point is is impossible to have an
+   optional libpthread and call pthread_atfork.
+
+   This code adds no more ABI requirements than already exist since
+   __dso_handle and __register_atfork are already part of the ABI.  */
+#include <pthread_atfork.c>