Re: [PATCH] nptl: Implement pthread_self in libc.so

[Florian Weimer <fweimer at redhat dot com>]

On 12/20/2017 08:16 AM, Carlos O'Donell wrote:

> > The stub implementation is broken, so we can't move more
> > functionality from libpthread to libc until it is fixed anyway.
>
> That could be fixed for just this case?

You mean, like adding a pthread_t == 0 check to those functions?  I 
think that's the wrong approach.

>   
> > > Are there thread functions we might use in a program not linked against
> > > libpthread e.g. the pthread_atfork changes we have in Fedora?
> >
> > pthread_thread_number_np depends on this change in practical terms.
>
> Why? In pthread_thread_number_np you can call THREAD_SELF directly?

The function does not call pthread_self, it has a pthread_t argument. 
Its test case crashe with a null pointer dereference if the pthread_self 
change is not applied first.

> > > > The layout of struct pthread_functions is not changed by this commit,
> > > > although the pointer used to store the address of pthread_self is now
> > > > unused.
> > >
> > > Why?
> >
> > To preserve the internal ABI.  It seem to have very little cost.  I
> > can remove the field, of course.
>
> I would prefer the removal. Please submit a v2.

Please consider the attached patch.

Thanks,
Florian

Subject: [PATCH] nptl: Implement pthread_self in libc.so
To: libc-alpha@sourceware.org

All binaries use TLS and thus need a properly set up TCB, so we can
simply return its address directly, instead of forwarding to the
libpthread implementation from libc.

For versioned symbols, the dynamic linker checks that the soname matches
the name supplied by the link editor, so a compatibility symbol in
libpthread is needed.

To avoid linking against the libpthread function in all cases, we would
have to bump the symbol version of libpthread in libc.so and supply a
compat symbol.  This commit does not do that because the function
implementation is so small, so the overhead by two active copies of the
same function might well be smaller than the increase in symbol table
size.

2017-12-20  Florian Weimer  <fweimer@redhat.com>

	nptl: Provide full implementation of pthread_self in libc.so.
	* nptl/Makefile (routines): Add pthread_self.
	(libpthread-routines): Replace pthread_self with
	compat-pthread_self.
	* nptl/forward.c (pthread_self): Remove.
	* nptl/nptl-init.c (pthread_functions): Do not initialize
	ptr_pthread_self.
	* nptl/pthread_self.c (pthread_self): Remove weak alias.
	* nptl/compat-pthread_self.c: New file.
	* sysdeps/nptl/pthread-functions.h (struct pthread_functions):
	Remove ptr_pthread_self.

diff --git a/nptl/Makefile b/nptl/Makefile
index 60d036a1ea..ab8cc98728 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -31,7 +31,7 @@ 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 pthread_self
 shared-only-routines = forward
 
 # We need to provide certain routines for compatibility with existing
@@ -49,7 +49,7 @@ pthread-compat-wrappers = \
 libpthread-routines = nptl-init vars events version pt-interp \
 		      pthread_create pthread_exit pthread_detach \
 		      pthread_join pthread_tryjoin pthread_timedjoin \
-		      pthread_self pthread_equal pthread_yield \
+		      compat-pthread_self pthread_equal pthread_yield \
 		      pthread_getconcurrency pthread_setconcurrency \
 		      pthread_getschedparam pthread_setschedparam \
 		      pthread_setschedprio \
diff --git a/nptl/compat-pthread_self.c b/nptl/compat-pthread_self.c
new file mode 100644
index 0000000000..5e9f4eb27d
--- /dev/null
+++ b/nptl/compat-pthread_self.c
@@ -0,0 +1,27 @@
+/* Compatibility version of pthread_self in libpthread.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   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/>.  */
+
+/* Compatibility version of pthread_self for old binaries which link
+   directly against libpthread's version.  */
+
+#include <shlib-compat.h>
+
+#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_27)
+# include "pthread_self.c"
+compat_symbol (libpthread, pthread_self, pthread_self, GLIBC_2_0);
+#endif
diff --git a/nptl/forward.c b/nptl/forward.c
index ac96765f29..8abbccdf5e 100644
--- a/nptl/forward.c
+++ b/nptl/forward.c
@@ -193,10 +193,6 @@ FORWARD (pthread_mutex_lock, (pthread_mutex_t *mutex), (mutex), 0)
 
 FORWARD (pthread_mutex_unlock, (pthread_mutex_t *mutex), (mutex), 0)
 
-
-FORWARD2 (pthread_self, pthread_t, (void), (), return 0)
-
-
 FORWARD (__pthread_setcancelstate, (int state, int *oldstate),
 	 (state, oldstate), 0)
 strong_alias (__pthread_setcancelstate, pthread_setcancelstate)
diff --git a/nptl/nptl-init.c b/nptl/nptl-init.c
index 869e926f17..a5979f27fd 100644
--- a/nptl/nptl-init.c
+++ b/nptl/nptl-init.c
@@ -122,7 +122,6 @@ static const struct pthread_functions pthread_functions =
     .ptr_pthread_mutex_init = __pthread_mutex_init,
     .ptr_pthread_mutex_lock = __pthread_mutex_lock,
     .ptr_pthread_mutex_unlock = __pthread_mutex_unlock,
-    .ptr_pthread_self = __pthread_self,
     .ptr___pthread_setcancelstate = __pthread_setcancelstate,
     .ptr_pthread_setcanceltype = __pthread_setcanceltype,
     .ptr___pthread_cleanup_upto = __pthread_cleanup_upto,
diff --git a/nptl/pthread_self.c b/nptl/pthread_self.c
index 8e21775e31..b75af9358e 100644
--- a/nptl/pthread_self.c
+++ b/nptl/pthread_self.c
@@ -19,10 +19,8 @@
 #include "pthreadP.h"
 #include <tls.h>
 
-
 pthread_t
-__pthread_self (void)
+pthread_self (void)
 {
   return (pthread_t) THREAD_SELF;
 }
-weak_alias (__pthread_self, pthread_self)
diff --git a/sysdeps/nptl/pthread-functions.h b/sysdeps/nptl/pthread-functions.h
index 4006fc6c25..4af21425d3 100644
--- a/sysdeps/nptl/pthread-functions.h
+++ b/sysdeps/nptl/pthread-functions.h
@@ -74,7 +74,6 @@ struct pthread_functions
 				 const pthread_mutexattr_t *);
   int (*ptr_pthread_mutex_lock) (pthread_mutex_t *);
   int (*ptr_pthread_mutex_unlock) (pthread_mutex_t *);
-  pthread_t (*ptr_pthread_self) (void);
   int (*ptr___pthread_setcancelstate) (int, int *);
   int (*ptr_pthread_setcanceltype) (int, int *);
   void (*ptr___pthread_cleanup_upto) (__jmp_buf, char *);