[webkit-dev] Build slave for JSCOnly Linux MIPS

Tue Apr 19 11:14:52 PDT 2016

I did a quick look over the trac query of GCC 4.8 changes that you provided.  None of the ones I looked at were scary but they were annoying.  They seemed to be things like:

- Sometimes saying { } to initialize a variable doesn’t work.
- Sometimes you need to say “const”.
- Sometimes you need to play with variables to get around internal compiler errors.

I didn’t find any cases of GCC 4.8 not supporting a language feature that we want to use.  Do you think that’s correct?

-Filip

> On Apr 19, 2016, at 11:02 AM, Michael Catanzaro <mcatanzaro at igalia.com> wrote:
> 
> Hi,
> 
> On Mon, 2016-04-18 at 17:27 -0700, Filip Pizlo wrote:
>> I am sympathetic to the principle that we should support the
>> compilers that ship on the most popular versions of Linux.
> 
> Great. :)
> 
>> I’d like to understand if that argument is sufficient to support GCC
>> 4.8.
>> 
>> Can you clarify, is it the case that if I installed the latest stable
>> Fedora, I’d get GCC 4.8?
> 
> No, all currently-supported versions of Fedora include GCC 5 (only).
> Different distros have very different release cycles and policies for
> compiler upgrades. Fedora releases roughly every six months, and each
> release is supported for roughly 13 months. GCC releases once per year.
> The GCC developers coordinate with Fedora release planning to time GCC
> releases to coincide with spring Fedora releases; in the winter before
> a new GCC release, we rebuilt all of Fedora with the GCC beta so the
> GCC developers can collect bug reports. So we will never have issues
> with Fedora, as the oldest Fedora will be at most one year behind
> upstream GCC. (Note that I co-maintain the WebKitGTK+ package there and
> I'm making sure all supported Fedoras get updates.)
> 
> But Fedora is exceptional in this regard. Other distros are supported
> for much longer than 13 months (5 years for Ubuntu LTS and newly also
> for Debian, 10 years for enterprise distros) and therefore have much
> older compilers. The question is where do we draw the line. We
> obviously cannot support a 10 year old distro; those are maintained by
> rich corporations, and if they cared about WebKit security, they could
> take responsibility for that. We could handle 5 years, but do we really
> want to? (It's clear Apple doesn't.) It's really inconvenient to not
> have access to newer dependencies or language features for so long. We
> might start by saying that we only support the latest release of [list
> of major distros that have recently been shipping WebKit updates]. Most
> of these distros are currently built using GCC 4.9, though they might
> have GCC 5 or GCC 6 packaged as well, but not used by default. The big
> one still using GCC 4.8 is openSUSE.
> 
> We don't *need* to consider Ubuntu right now, because they rarely ever
> take our updates, nor Debian, because they never take our updates. I
> think WebKit updates for Debian is all but totally a lost cause, but
> I'm kinda still hopeful for Ubuntu, so I'd like to keep them in mind.
> 
> Also, different distros have different policies on using alternative
> compilers. E.g. in Fedora we are usually required to always use
> Fedora's GCC, and only one version is available at a time... but if a
> package *really* has no chance of being built with GCC, we're allowed
> to use Fedora's Clang instead. I'm not sure what the policies are for
> Debian and Ubuntu, but they always have available a newer GCC than is
> used for building packages, and until recently were using Clang to
> build Chromium, so alternative compilers must be permitted at least in
> exceptional cases. I was trying to convince the openSUSE folks to use
> Clang to build WebKit, to avoid the GCC 4.8 issue, but they were not
> enthusiastic. (But consider that all these distros will have older
> versions of Clang as well.)
> 
> Now, whether openSUSE is important enough on its own to justify holding
> back or lowering our GCC requirement... maybe not. But anyway, since we
> have significant contributors like Konstantin stuck with GCC 4.8, and
> since this doesn't require giving up on any significant language
> features, I think it's OK. If it's only a little work to support that
> compiler (on the level we already have in trunk), I think it's a good
> idea.
> 
> But there is another problem here. openSUSE seems to have no intention
> of upgrading to a newer GCC anytime soon, because they have started to
> inherit core packages like GCC from the SUSE enterprise distro. So I
> might need to negotiate with them if it would be possible to build
> WebKit with clang after all.
> 
>> Can you clarify what you mean by “backport”?  I’m trying to get a
>> picture of how your releases work.  For example, are you saying that
>> RHEL wouldn’t take a security update that you backported, or that
>> they won’t invest energy into backporting it themselves?
> 
> We don't try to convince distros to take individual security fixes as
> patches, because there are way too many for that to be practical. We
> want them to take our tarball updates.
> 
> In that mail I was saying that RHEL won't invest energy into
> backporting things themselves downstream; consider that we have about
> 100 security fixes per year, backporting from trunk needs to be handled
> upstream so this can be shared among distros, rather than separately by
> each distro that wants to provide WebKit updates. Our upstream
> WebKitGTK+ releases work like this: every February and August, we
> branch off of trunk; this forms a new stable branch, which gets
> released in March/September. We then cherry-pick fixes to that branch
> and make releases off of it for the next seven months or so. Our goal
> is to convince distros to take these releases, because it's the only
> practical way for them to get security updates. I've recently had some
> mixed success with this; a couple big names like Mageia and openSUSE
> recently started taking our updates.
> 
> Some distros like Debian refuse to take any version upgrades at all,
> and want to fix everything with downstream patches. Since that is not
> practical for WebKit, they have adopted a policy of no security support
> for WebKit. Ubuntu leans towards this as well, but occasionally they do
> take our updates; I'm hoping that might become more common.
> 
> (RHEL is a bit of a special case in that its old enough that all apps
> in RHEL are using WebKit1, which we don't support anymore, so there's
> no value in taking our updates.)
> 
>> How many changes are required to make GCC 4.8 work?  I think this
>> will provide important context for this discussion.
> 
> I guess it's working already and we only need to remove the build error
> when it's detected, because Konstantin has been committing GCC 4.8
> fixes throughout the tree:
> 
> http://trac.webkit.org/search?q=4.8&noquickjump=1&changeset=on
> 
> Anyway, I do not strongly request that we drop the GCC requirement to
> GCC 4.8, though I think that would be fine; just please, we should keep
> these issues in mind when upgrading our compiler requirement in the
> future.
> 
> Michael