Re: [PATCH v8 16/29] arm64: Share arm64 headers with s390

[Steffen Eiden]

On Tue, Sep 29, 2026 at 06:00:12PM +0100, Catalin Marinas wrote:
> On Tue, Sep 29, 2026 at 06:19:20AM +0200, Andreas Grapentin wrote:
> > On Sep 28 26, Steffen Eiden wrote:
> > > On Mon, Sep 28, 2026 at 05:07:52PM +0100, Catalin Marinas wrote:
> > > > On Fri, Sep 18, 2026 at 03:30:53PM +0200, Steffen Eiden wrote:
> > > > > +# Enable all code shared to s390
> > > > > +KBUILD_CFLAGS	+= -DARM64_S390_COMMON
> > > > > +KBUILD_AFLAGS	+= -DARM64_S390_COMMON
> > > > > +KBUILD_CPPFLAGS	+= -DARM64_S390_COMMON
> > > > 
> > > > Do we actually need these defines? They seem only to be used as markers
> > > > for the awk scripts to extract the definitions. Why do we need the C
> > > > preprocessor involved at all? Could we not just have comment markers:
> > > > 
> > > > /* ARM64_S390_COMMON_BEGIN */
> > > > ...
> > > > /* ARM64_S390_COMMON_END */
> > > >
> > > No technically we do not need those. They could be useful if we find out
> > > that AWK is the wrong tool and move to a C Preprocessor + diff based
> > > approach. 
> > > 
> > > if the ifdev is not closed the compiler will complain, but an 'arm did
> > > not destroy us' verifiaction tool ( I will send one soonish) could do
> > > the same.
> > 
> > iirc the last time we discussed this we didn't think that load-bearing
> > comments were the right tool here. We also briefly floated the idea of
> > using a #pragma region based approach, but in the end we went with the
> > #ifdef preprocessor directives instead, as the least invasive
> > non-comment marker that was available.
> 
> The downside is that the macro affects the preprocessed code. We need to
> ensure they don't leak in uapi headers for example. Not a fan of this
> approach but I don't have a better suggestion either. At least we could
> write them as:
> 
> #if ARM64_S390_COMMON == 1

This is a great idea and an improvement. Thanks.

@Marc: Shall I sent a v9 of this series or do you want to pick v8 and I
send this as an improvement once picked?

Regarding UAPI: We will either import the whole uapi header or noting.
We will not modify ARM uapi headers for the arm64 on s390 feature.

> 
> so we get an error if someone misspells the macro name (or they leak in
> uapi headers, vDSO).
> 
> It would also be useful for the awk scripts look for the paired #endif
> rather than relying on the comment at the end of the line. Otherwise
> it's not really different from just sticking to comments.
> 

Are you suggesting that the AWK scripts should track the #if% and #endif
in the code and warn or reject if the marked endif for the shared code
does not match pairing with the starting #if? That makes sense yes. I'll
investigate and would add this as an improvement later on.

	Steffen