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

[Palmer Dabbelt]

On Mon, 09 Dec 2024 08:33:43 PST (-0800), mjeanson@efficios.com wrote:
> 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.

Sorry, I thought this was already reviewed/ack'd

Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>

> Thanks,
>
> Michael