discussion related to source for porting headers and methods to RTEMS and newlib

[Joel Sherrill]

On Tue, Mar 24, 2020 at 5:33 PM Gedare Bloom <gedare at rtems.org> wrote:

> email subject can be shortened. almost everything is a discussion :)
>
> On Tue, Mar 24, 2020 at 3:49 PM Eshan Dhawan <eshandhawan51 at gmail.com>
> wrote:
> >
> > Hello everyone,
> > I have identified sources to port headers and methods to RTEMS and
> Newlib. I have given priority to FreeBSD for the choice of source. But
> method not present in FreeBSD can be ported from alternative sources like
> NetBSD and musl.
> >
> Considering the simplicity, you may want to compare musl vs freebsd as
> well.
>
> > -> Missing methods of math.h: I have compiled a list of methods and
> their sources. Some need to be implemented from scratch.
> > list: Math.h missing functions
> >
> > -> sys/ipc.h: This header and its function can be ported from FreeBSD.
> > ipc.h : https://github.com/freebsd/freebsd/blob/master/sys/sys/ipc.h
> > ftok.c:
> https://github.com/freebsd/freebsd/blob/master/lib/libc/gen/ftok.c


sys/ipc.h has a lot in it. If you head down the path of adding sys/ipc.h,
you need to evaluate what else is in the file.

Adding support for the System V style SHM, Semaphores, or Message Queues is
possible (I think) but is definitely harder than the likely value to the
community.

>
> >
> > ->fmtmsg.h: its implementation is also present in FreeBSD.
> > https://github.com/freebsd/freebsd/blob/master/include/fmtmsg.h
> > https://github.com/freebsd/freebsd/blob/master/lib/libc/gen/fmtmsg.c


By my recollection, this would be a discrete thing to add to Newlib.


>
> >
> > ->spawn.h: Its implementation is in FreeBSD.
> >
> https://github.com/freebsd/freebsd/blob/master/lib/libc/gen/posix_spawn.c
> >
> I'm worried about the large number of includes there. It may easily
> lead you to trouble chasing down transitive include headers, like what
> happened with Vaibhav before with search.h support.
>

posix_spawn() cannot be supported by RTEMS. It is a new safer way to do
fork/exec. Don't spent any time on this. It will never work on RTEMS.

It is also a HUGE amount of methods and constants. :(

>
> > -> pselect() from <sys/select.h> : its implementation is also from
> FreeBSD
> > https://github.com/freebsd/freebsd/blob/master/lib/libc/sys/pselect.c


This would be added to rtems-libbsd. There may be specific technical
challenges
why it is not present. Or it could just be an oversight.


>
> >
> > -> confstr() from <unistd.h>: Its implementation is from FreeBSD
> > https://github.com/udp/freebsd-libc/blob/master/gen/confstr.c.
>

The implementation of this would go in RTEMS.

It is possible that the FreeBSD code is a guide but this cannot be a direct
copy to port. Each value defined by POSIX as fetchable must be properly
defined for RTEMS. You would need to make a table of all the "names"
that can be looked up in your proposal.

FWIW I think the FreeBSD version is more right than wrong for RTEMS
but it can't be 100% right and needs analysis.

>
> > I would like everyone to review it and provide your suggestions.
> >
> include details in your proposal also.
>

+1

>
> > Thanks
> > -Eshan
>
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