linux-kernel - Re: [PATCH RESEND] Kbuild: Add an option to enable GCC VTA

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Date:	Mon, 24 Nov 2014 15:46:42 -0800
From:	Josh Stone <jistone@...hat.com>
To:	Michal Marek <mmarek@...e.cz>, linux-kernel@...r.kernel.org
CC:	"Frank Ch. Eigler" <fche@...hat.com>,
	Jakub Jelinek <jakub@...hat.com>,
	Josh Boyer <jwboyer@...oraproject.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Michel Dänzer 
	<michel@...nzer.net>
Subject: Re: [PATCH RESEND] Kbuild: Add an option to enable GCC VTA

On 11/24/2014 01:46 PM, Michal Marek wrote:
> Dne 21.11.2014 v 19:40 Josh Stone napsal(a):
>> Due to recent codegen issues, gcc -fvar-tracking-assignments was
>> unconditionally disabled in commit 2062afb4f804a ("Fix gcc-4.9.0
>> miscompilation of load_balance() in scheduler").  However, this reduces
> [...]
>> With gcc-4.9.2-1.fc22, I can now build v3.18-rc5 with Fedora's i686 and
>> x86_64 configs, and this is completely clean with GCC_COMPARE_DEBUG.
> 
> According to gcc's bug#61801, this is really fixed in 4.9.2 (commit
> 556537c4 in the git mirror). So how about checking for this minimal
> version instead of a new Kconfig option?

That's possible, if the new Kconfig option is really undesirable.  But
given that there's a similar DWARF4 option, which this pairs well with,
I thought a VTA option was a good choice.

Besides 4.9.2 though, this particular fix has also been backported to
4.8.4, and who knows what various distro maintainers may do.
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