Re: [PATCH] IBM zSystems: Fix TARGET_D_CPU_VERSIONS

[Stefan Schulze Frielinghaus <stefansf@linux.ibm.com>]

On Mon, Jan 23, 2023 at 02:21:46PM +0100, Iain Buclaw wrote:
> Excerpts from Stefan Schulze Frielinghaus via Gcc-patches's message of Januar 13, 2023 6:54 pm:
> > In the context of D the interpretation of S390, S390X, and SystemZ is a
> > bit fuzzy.  The wording S390X was wrongly deprecated in favour of
> > SystemZ by commit
> > https://github.com/dlang/dlang.org/commit/3b50a4c3faf01c32234d0ef8be5f82915a61c23f
> > Thus, SystemZ is used for 64-bit targets, now, and S390 for 31-bit
> > targets.  However, in TARGET_D_CPU_VERSIONS depending on TARGET_ZARCH we
> > set the CPU version to SystemZ.  This is also the case if compiled for
> > 31-bit targets leading to the following error:
> > 
> > libphobos/libdruntime/core/sys/posix/sys/stat.d:967:13: error: static assert:  '96u == 144u' is false
> >   967 |             static assert(stat_t.sizeof == 144);
> >       |             ^
> > 
> 
> So that I follow, there are three possible combinations?
> 
> ESA 31-bit (S390)
> ESA 64-bit (what was S390X)
> z/Arch 64-bit (SystemZ)

There are three combinations:

- s390:  32-bit ABI and ESA mode
- s390:  32-bit ABI and z/Architecture mode
- s390x: 64-bit ABI and z/Architecture mode

Note, depending on the CPU mode z/Architecture is supported by the
32- and 64-bit ABI whereas ESA is only supported by the 32-bit ABI.

Thus, s390 always refers to the 32-bit ABI but does not fix the
instructions set architecture (ESA or z/Architecture).  Whereas s390x
refers to the 64-bit ABI for which only z/Architecture exists.

While nitpicking, typically the target is written in lower case letters,
i.e., not S390X but s390x and likewise s390 instead of S390.

Hope this clarifies the set of possible combinations.  Let me know if
anything else is unclear.

> 
> > Thus in order to keep this patch simple I went for keeping SystemZ for
> > 64-bit targets and S390, as usual, for 31-bit targets and dropped the
> > distinction between ESA and z/Architecture.
> > 
> > Bootstrapped and regtested on IBM zSystems.  Ok for mainline?
> > 
> 
> OK by me.  Maybe keep both S390X and SystemZ for TARGET_64BIT? There's
> only ever been a binary distinction as far as I'm aware.

Sounds good to me.  I will come up with an updated patch.

Cheers,
Stefan