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Re: [PATCH] nptl: Implement pthread_self in libc.so
On 12/19/2017 11:53 PM, Florian Weimer wrote:
> 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.
Sure, but I acknowledge that your point is valid, that pthread_self
should just work reliably.
>>>> 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.
Thanks. That's what I expected was the case.
>>>>> 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.
This version looks good to me.
Would we consider this a fix for an externally visible bug?
Namely that a user could call pthread_self() in a program not
linked to libpthread, and get back a 0 value which can't be
used in subsequent POSIX thread functions without crashing?
Next steps:
- File a bug if you agree with the above.
- Commit this change with the bug number attached.
> Thanks,
> Florian
>
> pthread_self.patch
>
>
> 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 *);
--
Cheers,
Carlos.