[PATCH v5] nptl: Add <thread_pointer.h> for RISC-V

[Michael Jeanson]

On 2024-11-01 12:41, 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 tested on a Visionfive 2 with Debian sid.
> 
> Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
> ---
> Changes since v4:
> - Revert to GCC/Clang version check, __has_builtin can't reliably detect
>   if __builtin_thread_pointer is implemented in the backend
> Changes since v3:
> - Revert to inline asm for the fallback code
> Changes since v2:
> - The 'register' variable has to be global to generate the correct asm
> - Reuse '__thread_self' from 'tls.h'
> Changes since v1:
> - Use __glibc_has_builtin instead of GCC version check
> - Use 'register' variable instead of inline asm
> ---
> Cc: Florian Weimer <fweimer@redhat.com>
> Cc: Palmer Dabbelt <palmer@rivosinc.com>
> Cc: Darius Rad <darius@bluespec.com>
> Cc: Jeff Law <jeffreyalaw@gmail.com>
> ---
>  sysdeps/riscv/nptl/thread_pointer.h | 40 +++++++++++++++++++++++++++++
>  1 file changed, 40 insertions(+)
>  create mode 100644 sysdeps/riscv/nptl/thread_pointer.h
> 
> diff --git a/sysdeps/riscv/nptl/thread_pointer.h b/sysdeps/riscv/nptl/thread_pointer.h
> new file mode 100644
> index 0000000000..9e7a84a78b
> --- /dev/null
> +++ b/sysdeps/riscv/nptl/thread_pointer.h
> @@ -0,0 +1,40 @@
> +/* __thread_pointer definition.  riscv 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 <features.h>
> +
> +#if __GNUC_PREREQ (10, 3) || __glibc_clang_prereq (11, 0)
> +static inline void *
> +__thread_pointer (void)
> +{
> +  return __builtin_thread_pointer ();
> +}
> +#else
> +static inline void *
> +__thread_pointer (void)
> +{
> +  void *__thread_register;
> +  __asm__ ("mv %0, tp" : "=r" (__thread_register));
> +  return __thread_register;
> +}
> +#endif
> +
> +#endif /* _SYS_THREAD_POINTER_H */

Ping? I think we were in agreement on v4 and this is just a cleanup
of the builtin check. With a reviewed-by I could push this.

Thanks,

Michael