Re: Earliest version of gcc the project should support as stage1 for gcc 17?

On Fri, 20 Mar 2026 at 17:48, Claudio Bantaloukas
<[email protected]> wrote:
>
> On 20/03/2026 17:27, Jonathan Wakely wrote:
> > On Fri, 20 Mar 2026 at 15:58, Christophe Lyon via Gcc <[email protected]> wrote:
> >>
> >>
> >>
> >> On 3/20/26 11:15, Jakub Jelinek via Gcc wrote:
> >>> On Fri, Mar 20, 2026 at 09:47:08AM +0000, Claudio Bantaloukas via Gcc wrote:
> >>>> Title says it all really.
> >>>>
> >>>> Why am I asking? I'd like to try writing a build that checks stage1 works
> >>>> with the earliest version of gcc the project wants to support.
> >>>>
> >>>> https://gcc.gnu.org/install/prerequisites.html currently says:
> >>>> - GCC 5.4 or newer has sufficient support for used C++14 features.
> >>>> - If you need to build an intermediate version of GCC in order to bootstrap
> >>>> current GCC, consider GCC 9.5
> >>>>
> >>>> Should it use gcc 5.4? Is it time to increase that version?
> >>>
> >>> Yes. No.
> >>>
> >>> We don't increase the minimum requirement just for fun, but when it gives
> >>> significant benefits for the codebase and the earliest supported gcc is
> >>> still old enough (unlike especially rustc but also LLVM we try not to
> >>> require too recent stuff for building).
> >>> The reason to go to gcc 5.4 [1] (which already causes significant pain, several
> >>> CompilerFarm machines still have system gcc 4.8.5) was to be able to use
> >>> C++14 and so not be as limited in constexpr functions as in C++11.
> >>
> >> I believe Claudio is aiming at adding such builds in the forge CI (happy
> >> to help btw ;-) ), so I suppose a follow-up question is what distro &
> >> version should a container use?  Claudio shared a list in his message,
> >> none of which matches the exact 5.4 requirement.
> >>
> >> Does this mean starting with an ubuntu-16.04 (ships gcc-5.3.1) and
> >> build/install gcc-5.4.0 in it, and use the resulting image?
>
> Cristophe, you're right, I've been wanting to add such a check for a
> while. But I'd like to add a twist to it. Rather than use an unsupported
> operating system, requiring vsyscall emulation, I'd rather try and build
> an older version of gcc on top of a new distribution.
>
> > Well based on what Jakub said, the Ubuntu 5.3.1 might be OK to build trunk.
> >
> > Until a few weeks ago, I was building every trunk snapshot using the
> > Ubuntu 16:04 system compiler. I switched to 18:04 because something
> > was failing, but I don't know if it was a temporary breakage on trunk.
>
> I guess we'll find out at some point :)

The gcc-16-20260315 snapshot builds fine on Ubuntu 16:04, I just tried it.