Re: [PATCH] parisc: futex: Use same lock set as lws calls

["Carlos O'Donell" <carlos@xxxxxxxxxxxxxxxx>]

On Wed, Oct 19, 2011 at 9:47 PM, John David Anglin <dave.anglin@xxxxxxxx> wrote:
> I looked at this a bit.  The problem is legitimize_tls_address doesn't work
> properly. First, GCC doesn't know that the libcall needs r26 and ret0 when the
> __thread variable is an argument to a call.  Secondly, the implementation of __tls_get_addr
> clobbers some other call clobbered registers.  I'm thinking the glibc implementation
> might need to be in assembly language so that the clobbered registers are limited (i.e.,
> it needs to save registers).   This all seems really ugly...
>
> The issues occur in generating PIC code.

Yes, __tls_get_addr is a normal C function and follows normal function
register usage.

Why does __tls_get_addr need to be a special function?

Almost all the targets in glibc-ports have C versions of __tls_get_addr.

For example I notice that on Alpha the call to __tls_get_addr is *not*
done via a emit_library_call_value, instead they use some emit_insn,
emit_libcall_block and use_reg.

So it looks like they tamper with the register usage via use_reg
before the call to __tls_get_addr?

Another example is Sparc which also uses a custom sequence and
manipulates the used registers.

I think our legitimize_tls_address needs to be rewritten to match
something like what alpha or sparc has, otherwise we are going to run
into trouble trying to get emit_library_call_value to work correctly.

Cheers,
Carlos.
--
To unsubscribe from this list: send the line "unsubscribe linux-parisc" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html