Re: [PATCH v3 02/13] tcg/s390x: Remove TCG_REG_TB

[Thomas Huth]

On 06/12/2022 23.22, Richard Henderson wrote:
> On 12/6/22 13:29, Ilya Leoshkevich wrote:
> > On Thu, Dec 01, 2022 at 10:51:49PM -0800, Richard Henderson wrote:
> > > This reverts 829e1376d940 ("tcg/s390: Introduce TCG_REG_TB"), and
> > > several follow-up patches.  The primary motivation is to reduce the
> > > less-tested code paths, pre-z10.  Secondarily, this allows the
> > > unconditional use of TCG_TARGET_HAS_direct_jump, which might be more
> > > important for performance than any slight increase in code size.
> > >
> > > Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> > > ---
> > >   tcg/s390x/tcg-target.h     |   2 +-
> > >   tcg/s390x/tcg-target.c.inc | 176 +++++--------------------------------
> > >   2 files changed, 23 insertions(+), 155 deletions(-)
> >
> > Reviewed-by: Ilya Leoshkevich <iii@linux.ibm.com>
> >
> > I have a few questions/ideas for the future below.
> > > diff --git a/tcg/s390x/tcg-target.h b/tcg/s390x/tcg-target.h
> > > index 22d70d431b..645f522058 100644
> > > --- a/tcg/s390x/tcg-target.h
> > > +++ b/tcg/s390x/tcg-target.h
> > > @@ -103,7 +103,7 @@ extern uint64_t s390_facilities[3];
> > >   #define TCG_TARGET_HAS_mulsh_i32      0
> > >   #define TCG_TARGET_HAS_extrl_i64_i32  0
> > >   #define TCG_TARGET_HAS_extrh_i64_i32  0
> > > -#define TCG_TARGET_HAS_direct_jump    HAVE_FACILITY(GEN_INST_EXT)
> > > +#define TCG_TARGET_HAS_direct_jump    1
> >
> > This change doesn't seem to affect that, but what is the minimum
> > supported s390x qemu host? z900?
>
> Possibly z990, if I'm reading the gcc processor_flags_table[] correctly; 
> long-displacement-facility is definitely a minimum.
>
> We probably should revisit what the minimum for TCG should be, assert those 
> features at startup, and drop the corresponding runtime tests.

If we consider the official IBM support statement:

https://www.ibm.com/support/pages/system/files/inline-files/IBM%20Mainframe%20Life%20Cycle%20History%20V2.10%20-%20Sept%2013%202022_1.pdf

... that would mean that the z10 and all older machines are not supported 
anymore.

 Thomas