Re: [RFC PATCH glibc 24/34] hurd: Only check for TLS initialization inside rtld or in static builds

[Samuel Thibault <samuel.thibault@gnu.org>]

I have reverted that change for now, so we get back to a working glibc.

Samuel

Samuel Thibault, le mar. 11 avril 2023 20:57:05 +0200, a ecrit:
> Hello,
> 
> Had you actually tested it on i386? It seems to be breaking the
> testsuite completely. I would expect that a submitted patch series has
> gone through the testsuite.
> 
> Sergey Bugaev, le dim. 19 mars 2023 18:10:07 +0300, a ecrit:
> > When glibc is built as a shared library, TLS is always initialized by
> > the call of TLS_INIT_TP () macro made inside the dynamic loader, prior
> > to running the main program (see dl-call_tls_init_tp.h).
> 
> Yes, but apparently we load libc.so before calling TLS_INIT_TP? (and
> thus start using its functions)
> 
> Samuel
> 
> > We can take
> > advantage of this: we know for sure that __LIBC_NO_TLS () will evaluate
> > to 0 in all other cases, so let the compiler know that explicitly too.
> > 
> > Also, only define _hurd_tls_init () and TLS_INIT_TP () under the same
> > conditions (either !SHARED or inside rtld), to statically assert that
> > this is the case.
> > 
> > Other than a microoptimization, this also helps with avoiding awkward
> > sharing of the __libc_tls_initialized variable between ld.so and libc.so
> > that we would have to do otherwise -- we know for sure that no sharing
> > is required, simply because __libc_tls_initialized would always be set
> > to true inside libc.so.
> > 
> > Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
> > ---
> >  sysdeps/mach/hurd/Makefile                    |  4 ++
> >  sysdeps/mach/hurd/i386/dl-tls-initialized.c   | 21 +++++++++
> >  sysdeps/mach/hurd/i386/tls.h                  | 43 +++++++++++--------
> >  sysdeps/mach/hurd/x86/init-first.c            | 11 +----
> >  sysdeps/mach/hurd/x86_64/dl-tls-initialized.c | 21 +++++++++
> >  sysdeps/mach/hurd/x86_64/tls.h                | 19 +++++---
> >  6 files changed, 85 insertions(+), 34 deletions(-)
> >  create mode 100644 sysdeps/mach/hurd/i386/dl-tls-initialized.c
> >  create mode 100644 sysdeps/mach/hurd/x86_64/dl-tls-initialized.c
> > 
> > diff --git a/sysdeps/mach/hurd/Makefile b/sysdeps/mach/hurd/Makefile
> > index d5584930..f43e92ba 100644
> > --- a/sysdeps/mach/hurd/Makefile
> > +++ b/sysdeps/mach/hurd/Makefile
> > @@ -197,6 +197,10 @@ ifeq (hurd, $(subdir))
> >  sysdep_routines += cthreads
> >  endif
> >  
> > +ifeq (elf, $(subdir))
> > +sysdep-dl-routines += dl-tls-initialized
> > +endif
> > +
> >  ifeq (io, $(subdir))
> >  sysdep_routines += f_setlk close_nocancel close_nocancel_nostatus \
> >  		   fcntl_nocancel open_nocancel openat_nocancel read_nocancel \
> > diff --git a/sysdeps/mach/hurd/i386/dl-tls-initialized.c b/sysdeps/mach/hurd/i386/dl-tls-initialized.c
> > new file mode 100644
> > index 00000000..493ec239
> > --- /dev/null
> > +++ b/sysdeps/mach/hurd/i386/dl-tls-initialized.c
> > @@ -0,0 +1,21 @@
> > +/* Determine whether TLS is initialized, for i386/Hurd.
> > +   Copyright (C) 1995-2023 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
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#ifndef SHARED
> > +unsigned short __init1_desc;
> > +#endif
> > diff --git a/sysdeps/mach/hurd/i386/tls.h b/sysdeps/mach/hurd/i386/tls.h
> > index 0f8dd241..ee7b8004 100644
> > --- a/sysdeps/mach/hurd/i386/tls.h
> > +++ b/sysdeps/mach/hurd/i386/tls.h
> > @@ -69,18 +69,6 @@ _Static_assert (offsetof (tcbhead_t, __private_ss) == 0x30,
> >                    |  (desc->high_word & 0xff000000));			      \
> >    })
> >  
> > -/* Return 1 if TLS is not initialized yet.  */
> > -#ifndef SHARED
> > -extern unsigned short __init1_desc;
> > -#define __HURD_DESC_INITIAL(gs, ds) ((gs) == (ds) || (gs) == __init1_desc)
> > -#else
> > -#define __HURD_DESC_INITIAL(gs, ds) ((gs) == (ds))
> > -#endif
> > -
> > -#define __LIBC_NO_TLS()							      \
> > -  ({ unsigned short ds, gs;						      \
> > -     asm ("movw %%ds,%w0; movw %%gs,%w1" : "=q" (ds), "=q" (gs));	      \
> > -     __builtin_expect(__HURD_DESC_INITIAL(gs, ds), 0); })
> >  #endif
> >  
> >  /* The TCB can have any size and the memory following the address the
> > @@ -125,6 +113,28 @@ extern unsigned short __init1_desc;
> >  
> >  # define HURD_SEL_LDT(sel) (__builtin_expect ((sel) & 4, 0))
> >  
> > +#ifndef SHARED
> > +extern unsigned short __init1_desc;
> > +# define __HURD_DESC_INITIAL(gs, ds) ((gs) == (ds) || (gs) == __init1_desc)
> > +#else
> > +# define __HURD_DESC_INITIAL(gs, ds) ((gs) == (ds))
> > +#endif
> > +
> > +#if !defined (SHARED) || IS_IN (rtld)
> > +/* Return 1 if TLS is not initialized yet.  */
> > +extern inline bool __attribute__ ((unused))
> > +__LIBC_NO_TLS (void)
> > +{
> > +  unsigned short ds, gs;
> > +  asm ("movw %%ds, %w0\n"
> > +       "movw %%gs, %w1"
> > +       : "=q" (ds), "=q" (gs));
> > +  return __glibc_unlikely (__HURD_DESC_INITIAL (gs, ds));
> > +}
> > +
> > +/* Code to initially initialize the thread pointer.  This might need
> > +   special attention since 'errno' is not yet available and if the
> > +   operation can cause a failure 'errno' must not be touched.  */
> >  static inline bool __attribute__ ((unused))
> >  _hurd_tls_init (tcbhead_t *tcb)
> >  {
> > @@ -168,11 +178,10 @@ out:
> >    return success;
> >  }
> >  
> > -/* Code to initially initialize the thread pointer.  This might need
> > -   special attention since 'errno' is not yet available and if the
> > -   operation can cause a failure 'errno' must not be touched.  */
> > -# define TLS_INIT_TP(descr) \
> > -    _hurd_tls_init ((tcbhead_t *) (descr))
> > +# define TLS_INIT_TP(descr) _hurd_tls_init ((tcbhead_t *) (descr))
> > +#else /* defined (SHARED) && !IS_IN (rtld) */
> > +# define __LIBC_NO_TLS() 0
> > +#endif
> >  
> >  # if __GNUC_PREREQ (6, 0)
> >  
> > diff --git a/sysdeps/mach/hurd/x86/init-first.c b/sysdeps/mach/hurd/x86/init-first.c
> > index 48c330ec..89a5f44c 100644
> > --- a/sysdeps/mach/hurd/x86/init-first.c
> > +++ b/sysdeps/mach/hurd/x86/init-first.c
> > @@ -40,13 +40,6 @@ extern char **_dl_argv;
> >  
> >  #ifndef SHARED
> >  static tcbhead_t __init1_tcbhead;
> > -# ifndef __x86_64__
> > -unsigned short __init1_desc;
> > -# endif
> > -#endif
> > -
> > -#ifdef __x86_64__
> > -unsigned char __libc_tls_initialized;
> >  #endif
> >  
> >  /* Things that want to be run before _hurd_init or much anything else.
> > @@ -166,9 +159,7 @@ first_init (void)
> >    _hurd_tls_init (&__init1_tcbhead);
> >  
> >    /* Make sure __LIBC_NO_TLS () keeps evaluating to 1.  */
> > -# ifdef __x86_64__
> > -  __libc_tls_initialized = 0;
> > -# else
> > +# ifndef __x86_64__
> >    asm ("movw %%gs,%w0" : "=m" (__init1_desc));
> >  # endif
> >  #endif
> > diff --git a/sysdeps/mach/hurd/x86_64/dl-tls-initialized.c b/sysdeps/mach/hurd/x86_64/dl-tls-initialized.c
> > new file mode 100644
> > index 00000000..d0766f95
> > --- /dev/null
> > +++ b/sysdeps/mach/hurd/x86_64/dl-tls-initialized.c
> > @@ -0,0 +1,21 @@
> > +/* Determine whether TLS is initialized, for x86_64/Hurd.
> > +   Copyright (C) 1995-2023 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
> > +   <https://www.gnu.org/licenses/>.  */
> > +
> > +#if !defined (SHARED) || IS_IN (rtld)
> > +unsigned short __libc_tls_initialized;
> > +#endif
> > diff --git a/sysdeps/mach/hurd/x86_64/tls.h b/sysdeps/mach/hurd/x86_64/tls.h
> > index cf74e1f4..da504d9c 100644
> > --- a/sysdeps/mach/hurd/x86_64/tls.h
> > +++ b/sysdeps/mach/hurd/x86_64/tls.h
> > @@ -68,10 +68,6 @@ _Static_assert (offsetof (tcbhead_t, stack_guard) == 0x28,
> >  _Static_assert (offsetof (tcbhead_t, __private_ss) == 0x70,
> >                  "split stack pointer offset");
> >  
> > -extern unsigned char __libc_tls_initialized;
> > -
> > -# define __LIBC_NO_TLS() __builtin_expect (!__libc_tls_initialized, 0)
> > -
> >  /* The TCB can have any size and the memory following the address the
> >     thread pointer points to is unspecified.  Allocate the TCB there.  */
> >  # define TLS_TCB_AT_TP	1
> > @@ -87,8 +83,6 @@ extern unsigned char __libc_tls_initialized;
> >  # define TCB_ALIGNMENT	64
> >  
> >  
> > -# define TLS_INIT_TP(descr) _hurd_tls_init ((tcbhead_t *) (descr))
> > -
> >  # define THREAD_SELF							\
> >    (*(tcbhead_t * __seg_fs *) offsetof (tcbhead_t, tcb))
> >  /* Read member of the thread descriptor directly.  */
> > @@ -174,6 +168,10 @@ _hurd_tls_new (thread_t child, tcbhead_t *tcb)
> >                               i386_FSGS_BASE_STATE_COUNT);
> >  }
> >  
> > +# if !defined (SHARED) || IS_IN (rtld)
> > +extern unsigned char __libc_tls_initialized;
> > +#  define __LIBC_NO_TLS() __builtin_expect (!__libc_tls_initialized, 0)
> > +
> >  static inline bool __attribute__ ((unused))
> >  _hurd_tls_init (tcbhead_t *tcb)
> >  {
> > @@ -184,11 +182,18 @@ _hurd_tls_init (tcbhead_t *tcb)
> >    tcb->multiple_threads = 1;
> >  
> >    err = _hurd_tls_new (self, tcb);
> > +  if (err == 0)
> > +    __libc_tls_initialized = 1;
> >    __mach_port_deallocate (__mach_task_self (), self);
> > -  __libc_tls_initialized = 1;
> >    return err == 0;
> >  }
> >  
> > +#  define TLS_INIT_TP(descr) _hurd_tls_init ((tcbhead_t *) (descr))
> > +# else /* defined (SHARED) && !IS_IN (rtld) */
> > +#  define __LIBC_NO_TLS() 0
> > +# endif
> > +
> > +
> >  
> >  /* Global scope switch support.  */
> >  # define THREAD_GSCOPE_FLAG_UNUSED 0
> > -- 
> > 2.39.2
> > 
> 
> -- 
> Samuel
> ---
> Pour une évaluation indépendante, transparente et rigoureuse !
> Je soutiens la Commission d'Évaluation de l'Inria.

-- 
Samuel
---
Pour une évaluation indépendante, transparente et rigoureuse !
Je soutiens la Commission d'Évaluation de l'Inria.