linux-kernel - Re: [BUILD FAILURE] nfs4state.c fails to compile with gcc 4.5.4

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Date:   Thu, 30 Nov 2017 13:28:23 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        Anna Schumaker <Anna.Schumaker@...app.com>,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>
Subject: Re: [BUILD FAILURE] nfs4state.c fails to compile with gcc 4.5.4

On Thu, Nov 30, 2017 at 4:39 AM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Wed, 29 Nov 2017 19:27:45 -0800 Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>
>> On Wed, Nov 29, 2017 at 6:58 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
>> >
>> > Seems it can't handle the initialization of an anonymous struct within
>> > an anonymous union.
>>
>> I think we've seen this before, and I think there was some trick to
>> make it work with older gcc versions.
>>
>> Maybe the unnamed entry that gets initialized had to be declared
>> first, and the initializer needed an extra set of braces?
>>
>> Something like that.
>>
>> But maybe the answer is just to say "4.5.4 is really old".
>>
>> Doing some log digging gives me
>>
>>     ee9d3429c0e4 ("net/sched/sch_red.c: work around gcc-4.4.4 anon
>> union initializer issue")
>>     aa4bf44dc851 ("userns: use union in {g,u}idmap struct")
>>     6c09ffd02725 ("irqchip/gic-v4: Fix building with ancient gcc")
>>     c848c49a62b3 ("drivers/media/cec/cec-adap.c: fix build with gcc-4.4.4")
>>
>> but they aren't necessarily _exactly_ the same issue.
>
> Yeah, I'm the world expert at working around this gcc bug but the nfs4
> one had me stumped when I looked at it, so I shelved it for revisiting
> later.
>
> It would be nice to fix it, given that this is the only (known) site in
> the kernel which rules out these compiler versions.

There are more in drivers/irqchip/irq-gic-v4.c and virt/kvm/arm/vgic/, but
they are not built on x86. I've fixed it before, but it seems to be coming
back each time a new GIC variant gets added.

If anyone cares, I can find the remaining patches I have for this and
send them again.

      Arnd