On Thu, 2018-03-01 at 07:56 -0500, Roberto C. Sánchez wrote: > On Mon, Feb 26, 2018 at 11:06:03PM +0000, Ben Hutchings wrote: > > > > It will almost certainly build correctly with 4.9 on x86. AIUI the > > Spectre mitigations in gcc are x86-specific, so there's no value in > > changing it for ARM and there would be a risk of exceeding code size > > limits on armel. The kernel package already has provision for using > > different compiler versions per-architecture. > > > > So, I have let this issue alone for several days but there does not > appear to be much discussion, or even a consensus. I would really like > some definitive guidance (especially from people who know the kernel > better than I). > > As I do not know what would be involved in a gcc 4.9 backport or how > complex it would be, my intent to is to do the following: attempt to get > the wheezy kernel building in a jessie chroot with gcc-4.9 and, if that > succeeds, investigate the feasibility of building a gcc 4.9 backport for > wheezy. If that works, I envision there would be two advisories arising > from it: > > - a DLA for the new gcc-4.9 backport > - a DLA for an updated amd64 (and i386?) kernel build with gcc 4.9 The latter should not be done until I have also applied the Spectre v2 mitigations in assembly code. > Of course, if this looks like it would be substantially more complex, I > will again ask for guidance, but the likely course at that point seems > to implement the necessary option parsing in gcc 4.6. > > I suppose another possibility would be to backport the patches to gcc > 4.7 instead of 4.6 and switch the kernel build to gcc 4.7. Would that be > considered to introduce less risk than bringing gcc 4.9 into wheezy at > this stage? Unless you're experienced in gcc development, I would guess that using the existing patches for gcc 4.9 is lower risk. Ben. -- Ben Hutchings [W]e found...that it wasn't as easy to get programs right as we had thought. ... I realized that a large part of my life from then on was going to be spent in finding mistakes in my own programs. - Maurice Wilkes, 1949
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