Re: [PATCH 20/20] scripts/xeno-config: Allow disabling the y2038 / time64_t support

On Fri, 2026-02-20 at 15:50 +0100, Jan Kiszka wrote:
> On 20.02.26 10:09, Florian Bezdeka wrote:
> > xeno-config got a new cmdline option --disable-y2038 that will disable
> > the time64_t or (year 2038) support inside the application that is
> > being build against libcobalt.
> > 
> > libcobalt provides both interfaces, so for native time_t and for
> > time64_t at the same time. By default, the time64_t based interfaces
> > will be used. If an application does really want to go back to native
> > time_t --disable-y2038 has to be specified before the --cflags option.
> > 
> > The new parameter is only useful for (old) 32 bit applications.
> > 
> > Signed-off-by: Florian Bezdeka <[email protected]>
> > ---
> >  scripts/xeno-config-cobalt.in | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/scripts/xeno-config-cobalt.in b/scripts/xeno-config-cobalt.in
> > index 46b6c11b92fe20e4474e0173a211b18dc5cd7e3b..ecbfefb8f0a9f7ea99864d07e5f717841ef5da4e 100644
> > --- a/scripts/xeno-config-cobalt.in
> > +++ b/scripts/xeno-config-cobalt.in
> > @@ -62,6 +62,7 @@ Options :
> >          --core
> >          --info
> >          --compat
> > +        --disable-y2038
> >  EOF
> >      exit $1
> >  }
> > @@ -173,6 +174,9 @@ while test $# -gt 0; do
> >  	--posix|--cobalt|--vxworks|--psos|--alchemy|--rtdm|--smokey)
> >  	    skin_list="$skin_list `expr "$1" : '--\(.*\)'`"
> >  	    ;;
> > +	--disable-y2038)
> > +	    disable_y2038=y
> > +	    ;;
> >  	--cflags)
> >  	    do_cflags=y
> >  	    ;;
> > @@ -233,6 +237,7 @@ if test x$do_cflags = xy; then
> >  		;;
> >  	esac
> >      done
> > +    test x$disable_y2038 = xy && cflags="$cflags -U_TIME_BITS -U_FILE_OFFSET_BITS"
> 
> I did that undef in my mmap patch as well, but I wonder if - at least
> here - we couldn't filter out both defines from the given cflags.
> 

In case libcobalt itself was build with time64_t support those flags are
part of all cflags variables. Might be that there is a more elegant way
to remove flags but that didn't come to mind yet...

A different approach might be to skip writing the time64_t enablement
flags into XENO_USER_APP_CFLAGS (configure). Side effect might be that
every (testsuite) application has to enable the support on it's own,
doing all the glibc support checks...