Re: [PATCH] xen: add header guards to generated asm generic headers

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 5 Jun 2025, Jan Beulich wrote:
> On 05.06.2025 01:09, Stefano Stabellini wrote:
> > --- a/xen/scripts/Makefile.asm-generic
> > +++ b/xen/scripts/Makefile.asm-generic
> > @@ -32,7 +32,12 @@ old-headers := $(wildcard $(obj)/*.h)
> >  unwanted    := $(filter-out $(generic-y) $(generated-y),$(old-headers))
> >  
> >  quiet_cmd_wrap = WRAP    $@
> > -      cmd_wrap = echo "\#include <asm-generic/$*.h>" > $@
> > +      cmd_wrap = \
> > +   upper=$$(echo $*.h | tr a-z A-Z | tr '/.' '__'); \
> > +   printf "\#ifndef ASM_GENERIC_$${upper}\n" > $@; \
> > +   printf "\#define ASM_GENERIC_$${upper}\n" >> $@; \
> > +   printf "\#include <asm-generic/$*.h>\n" >> $@; \
> > +   printf "\#endif /* ASM_GENERIC_$${upper} */\n" >> $@
> 
> I'm curious: In what is now a0f56da94c3e I had to resort to "define" to
> get the rule to work (including a correct .*.cmd being generated). I
> can't claim I actually understood why things didn't work the "simple
> macro" way, and hence it's unclear to me whether the way it's done here
> will work with all make versions.

This works:

cmd_xlat_h = \
        printf "\#ifndef COMPAT_XLAT_H\n" >$@.new; \
        printf "\#define COMPAT_XLAT_H\n" >>$@.new; \
        cat $(filter %.h,$^) >>$@.new; \
        printf "" >>$@.new; \
        printf "\#endif /* COMPAT_XLAT_H */\n" >>$@.new; \
        mv -f $@.new $@

I made these changes:
- tab instead of spaces
- printf instead of echo
- escape # and add \n



> One further difference to that other commit: If make is interrupted in
> the middle of any of these printf-s, an incomplete file may remain. The
> cmd_xlat_h rule specifically uses "mv -f $@.new $@" to cover that corner
> case.

Good point I can fix it


> Finally - is ASM_GENERIC_$${upper} actually correct? Isn't that the
> guard that ought to be used _in_ asm-generic/$*.h?

You are right