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Re: [PATCH] S/390: Set ABI default based on uname
On Mon, Mar 12, 2018 at 06:42:15PM +0100, Andreas Krebbel wrote:
> On 03/12/2018 06:31 PM, Jakub Jelinek wrote:
> > On Mon, Mar 12, 2018 at 06:28:09PM +0100, Andreas Krebbel wrote:
> >> Currently the default ABI option for a GCC built on a 64 bit system is
> >> always -m64. This is inconvenient when e.g. building 32 bit libraries
> >> on a 64 bit system. The usual way to do this is to set the personality
> >> to s390 (32 bit) and let the configure script do the right thing.
> >> Having a GCC which defaults to -m64 also requires to get a -m31 somehow
> >> into the option list.
> >>
> >> With that patch the GCC driver checks the current personality setting in
> >> order to figure out at runtime what the default is supposed to be.
> >>
> >> Bootstrapped and regtested on s390x.
> >>
> >> I will commit the patch after waiting a few days for comments.
> >
> > I don't like this, it is inconsistent with how it is handled on all other
> > targets and how it worked for years. Having setarch magically change the
> > default is dangerous.
>
> Wow, that was quick ;)
>
> I didn't expect this to break things. Could you please elaborate where this might cause trouble?
It is an unexpected major behavior change for environments that are this way
used for 1-2 decades. When people want -m32 they just specify it, or if
they want a compiler that defaults to -m32 they configure it that way;
when gcc 7.x works one way and 8.x works differently, it will just mean
people will need to use -m32 or -m64 all the time, otherwise they won't be
sure what will happen.
Plus as I said, it is about consistency, why should s390x work in this
regard any differently in this regard from x86_64, powerpc64, sparc64,
mips64, which don't change the default even when setarch changes uname.
Jakub