RE: Build failures with gcc 4.5 and older

From: David Laight <David.Laight@ACULAB.COM>
To: 'Linus Torvalds' <torvalds@linux-foundation.org>
Cc: Guenter Roeck <linux@roeck-us.net>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Rik van Riel <riel@surriel.com>, "Mike Galbraith" <efault@gmx.de>,
	Dave Hansen <dave.hansen@intel.com>,
	"Andrew Morton" <akpm@linux-foundation.org>
Subject: RE: Build failures with gcc 4.5 and older
Date: Wed, 15 Aug 2018 16:18:26 +0000	[thread overview]
Message-ID: <d87ba353f6fc44668969a8535790cdc9@AcuMS.aculab.com> (raw)
In-Reply-To: <CA+55aFyeW7rqgGqOusZSz-jFP-CMH=hcyVGKhxyLxNeyBgLbqw@mail.gmail.com>

From: Linus Torvalds
> Sent: 15 August 2018 16:44
> On Wed, Aug 15, 2018 at 5:38 AM David Laight <David.Laight@aculab.com> wrote:
> >
> > Never mind the version of gcc, the x86 kernel doesn't build with the
> > default kernel options because the ORC unwinder hits a bug in libelf
> > (in objtool) that was only fixed late last year.
> >
> > It isn't even obvious from the build log what has gone wrong.
> 
> Can you give more details? We should try to work around it.
> 
> It's one thing to care about a compiler that is almost a decade old.
> At some point we just have to let it go.
> 
> But some libelf bug that is less than a year old is likely to bite people.

See https://lkml.org/lkml/2017/9/10/186 for the libelf fix.
It isn't anything like as rare as those emails suggest.
An 'allmodconfig' build fails on a lot of object files after 4.15-rc9.

When I fell over the problem I found a few reports on the ubuntu lists
but they all just said the ubuntu version was unsupported.

There is this patch I did https://lkml.org/lkml/2018/7/26/266 that got
no comments.

But really something needs to be done to objtool.

	David

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