[Libguestfs] [PATCH nbdkit 2/2] common/include/checked-overflow.h: Provide fallback

[Richard W.M. Jones]

On Mon, Nov 15, 2021 at 02:11:01PM +0100, Laszlo Ersek wrote:
> (2) Should nbdkit continue building on RHEL7? In the OCaml upgrade
> thread
> <https://listman.redhat.com/archives/libguestfs/2021-November/msg00095.html>
> I thought we practically abandoned RHEL7 for the v2v projects.

If I sound schizophrenic on RHEL 7 that'll be because I'm in two minds
still about supporting it.

In this particular case I was trying to test the OCaml changes on the
oldest version of OCaml I have easy access to and found that there
were various problems compiling on RHEL 7.  I fixed the other
problems, but this fix was a bit more controversial.

> (3) Red Hat Developer Toolset 10 (and 11 Beta) are available for RHEL7:
> 
> https://developers.redhat.com/products/developertoolset/overview
> 
> https://access.redhat.com/documentation/en-us/red_hat_developer_toolset/10/html/10.1_release_notes/system_requirements
> 
> https://access.redhat.com/documentation/en-us/red_hat_developer_toolset/11-beta/html/11.0_release_notes/system_requirements
> 
> providing gcc 10 and 11 respectively.
> 
> We could say that building nbdkit on RHEL7 requires devtoolset.

This doesn't sound very convenient, but there's a stronger reason to
keep stuff working with GCC 3/4 and that's because OpenBSD sticks with
GCC 4.2 as it was the last GPLv2+ version.  I think the reason OpenBSD
does this is wrong, but that's their choice.  (Of course they have
Clang).

> (1) I think that APIs that lie are wrong. I could contribute standard C
> implementations if we really think nbdkit should continue building on
> RHEL7. The difference with the built-ins should only be in performance,
> not in functionality.

I agree.  If you want to have a go at standard C versions that would
be great.  Even unsigned addition looks very hard.

I found this lengthy paper on the subject:
https://www.cs.utah.edu/~regehr/papers/overflow12.pdf

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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