[PATCH] nptl: Add <thread_pointer.h> for sparc

[Adhemerval Zanella Netto]

On 23/10/24 18:10, Michael Jeanson wrote:
> This will be required by the rseq extensible ABI implementation on all
> Linux architectures exposing the '__rseq_size' and '__rseq_offset'
> symbols to set the initial value of the 'cpu_id' field which can be used
> by applications to test if rseq is available and registered. As long as
> the symbols are exposed it is valid for an application to perform this
> test even if rseq is not yet implemented in libc for this architecture.
> 
> Both code paths are compile tested with build-many-glibcs.py but I don't
> have access to any hardware to run the tests.
> 
> Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
> ---
> Cc: Florian Weimer <fweimer@redhat.com>
> Cc: David S. Miller <davem@davemloft.net>
> Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
> Cc: Andreas K. Hüttel <dilfridge@gentoo.org>
> ---
>  sysdeps/sparc/nptl/thread_pointer.h | 36 +++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
>  create mode 100644 sysdeps/sparc/nptl/thread_pointer.h
> 
> diff --git a/sysdeps/sparc/nptl/thread_pointer.h b/sysdeps/sparc/nptl/thread_pointer.h
> new file mode 100644
> index 0000000000..76a666e586
> --- /dev/null
> +++ b/sysdeps/sparc/nptl/thread_pointer.h
> @@ -0,0 +1,36 @@
> +/* __thread_pointer definition.  sparc version.
> +   Copyright (C) 2021-2024 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 _SYS_THREAD_POINTER_H
> +#define _SYS_THREAD_POINTER_H
> +
> +#include <sys/cdefs.h>
> +
> +static inline void *
> +__thread_pointer (void)
> +{
> +#if __glibc_has_builtin (__builtin_thread_pointer)
> +  return __builtin_thread_pointer ();
> +#else

It does not seems to work on all gcc versions, with the testcase:

$ cat t.c
#include <sys/cdefs.h>

void *__thread_pointer (void)
{
#if __glibc_has_builtin (__builtin_thread_pointer)
  return __builtin_thread_pointer ();
#else
  void *__thread_register;
  __asm__ ("mov %%g7, %0" : "=r" (__thread_register));
  return __thread_register;
#endif
}

$ sparc64-glibc-linux-gnu-gcc -v 2>&1 | grep version
gcc version 14.2.1 20241007 [releases/gcc-14 r14-10750-g4af44f2cf7d] (GCC)

$ sparc64-glibc-linux-gnu-gcc t.c -S -o -
        .file   "t.c"
        .section        ".text"
t.c: In function ‘__thread_pointer’:
t.c:6:10: error: ‘__builtin_thread_pointer’ is not supported on this target
    6 |   return __builtin_thread_pointer ();
      |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~

> +  void *__thread_register;
> +  __asm__ ("mov %%g7, %0" : "=r" (__thread_register));
> +  return __thread_register;
> +#endif
> +}
> +
> +#endif /* _SYS_THREAD_POINTER_H */