[PATCH v4] nptl: Add <thread_pointer.h> for RISC-V

[Florian Weimer]

* Michael Jeanson:

> On 2024-10-16 17:16, 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.
>> 
>> A cleaner solution for the fallback code would be to use a global
>> 'register' variable, unfortunatly 'tls.h' a non-installed header already
>> defines '__thread_self' for the 'tp' register and GCC doesn't accept
>> multiple global register variables for the same register.
>
> Would it make more sense to move the global register variable '__thread_self'
> to the new 'thread_pointer.h' header and then include it in 'tls.h'?

I think we should not define a global register value in an installed
header because it may be in conflict with what the application is
doing.

Hopefully this will be irrelvant some day because every compiler in
use supports__builtin_thread_pointer.