Re: __tls_get_addr interface question.

Re: __tls_get_addr interface question.

[Martin Schwidefsky]

>The question is if it should be __tls_get_addr and not say __tls_get_offset
>on s390*...
__tls_get_offset would be a better name for it. 

>Would you be passing %r12 to that routine as another argument
>or would it have some assembly wrapper which would do that?
We get the best code if __tls_get_offset would just take one parameter.
The assembler wrapper would load the got pointer of the calling object
from %r12 before going to C code. This requires that a caller of
__tls_get_offset needs to setup the got register first.
A straightforward implementation of __tls_get_offset would be to
add the got pointer to the offset in the first parameter register
(add %r12 to %r2), call __tls_get_addr and then substract the TCB pointer
from the result (substract %a0 from %r2).
If this is too ugly we could add a second argument to __tls_get_offset but
that results in slightly worse code in the caller.

blue skies,
   Martin

Re: __tls_get_addr interface question.

[Jakub Jelinek]

On Tue, Jan 07, 2003 at 03:08:05PM +0100, Martin Schwidefsky wrote:
> Hi,
> we - that is Ulrich Weigand my myself - have started working on the
> TLS support for s390/s390x. I've done a preliminary binutils patch
> which seems to work. This version uses the standard IA-32 calling
> convention to __tls_get_addr. Now Ulrich came up with an idea
> how to improve the instruction sequences but this requires two
> changes to __tls_get_addr:
> 1) __tls_get_addr would be called with the got offset of a tls_index
>    structure located in the got instead of a pointer to the tls_index
>    structure. 
> 2) __tls_get_addr is to return the offset to the TCB of the variable
>    the tls_index refers to instead of the address.
> With these two changes we could improve the code quality for
> TLS accesses quite a bit.
> The question now is: can we have a s390/s390x version of
> __tls_get_addr with these changes without breaking anything?

The question is if it should be __tls_get_addr and not say __tls_get_offset
on s390*...
Would you be passing %r12 to that routine as another argument
or would it have some assembly wrapper which would do that?

	Jakub

__tls_get_addr interface question.

[Martin Schwidefsky]

Hi,
we - that is Ulrich Weigand my myself - have started working on the
TLS support for s390/s390x. I've done a preliminary binutils patch
which seems to work. This version uses the standard IA-32 calling
convention to __tls_get_addr. Now Ulrich came up with an idea
how to improve the instruction sequences but this requires two
changes to __tls_get_addr:
1) __tls_get_addr would be called with the got offset of a tls_index
   structure located in the got instead of a pointer to the tls_index
   structure. 
2) __tls_get_addr is to return the offset to the TCB of the variable
   the tls_index refers to instead of the address.
With these two changes we could improve the code quality for
TLS accesses quite a bit.
The question now is: can we have a s390/s390x version of
__tls_get_addr with these changes without breaking anything?

blue skies,
  Martin.