Re: [Qemu-devel] [PATCH 09/15] tcg-sparc: Do not use a global register for AREG0.

[Blue Swirl]

On Mon, Mar 26, 2012 at 16:52, Richard Henderson <address@hidden> wrote:
> On 03/26/12 09:31, Blue Swirl wrote:
>>> > +/* In dyngen-exec.h, without AREG0, we fall back to an alias to 
>>> > cpu_single_env.
>>> > +   We can't actually tell from here whether that's needed or not, but it 
>>> > does
>>> > +   not hurt to go ahead and make the declaration.  */
>>> > +#ifndef CONFIG_TCG_PASS_AREG0
>>> > +extern
>>> > +#ifdef __linux__
>>> > +  __thread
>>> > +#endif
>>> > +  CPUArchState *env __attribute__((alias("tls__cpu_single_env")));
>>> > +#endif /* CONFIG_TCG_PASS_AREG0 */
>> Please use DECLARE_TLS/DEFINE_TLS and global env accesses should also
>> use tls_var().
>>
>
> That won't work.
>
> This is intended to be a drop-in replacement for the "env" symbol that
> we declare in dyngen-exec.h.  For all other hosts, this symbol is a
> global register variable.  We can't go wrapping tls_var around all uses
> in all target backends.
>
> As I say in the comment, the most natural replacement is a preprocessor
> macro, but then that fails with the uses of "env" in the DEF_HELPER_N
> macros.
>
> Which leaves no alternative -- short of converting *all* targets to
> CONFIG_TCG_PASS_AREG0 first -- except the symbol alias you see there.

But at that point there will be no global env use anymore, so
dyngen-exec.h etc. can be removed. Perhaps this patch and its
dependencies should wait for that to happen. As an intermediate hack
it's sort of OK.

> Hmm... actually... I'm wrong about the use of preprocessor macros.
> The simple solution there is to re-order the includes on a few ports.
> I.e. "helper.h" must come before "dyngen-exec.h".  Now that's a much
> simpler fix...

OK.

>
>
> r~