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Date: Fri, 10 Oct 2014 20:44:33 -0500 From: Nathan Lynch <Nathan_Lynch@...tor.com> To: Russell King - ARM Linux <linux@....linux.org.uk> CC: Felipe Balbi <balbi@...com>, Rik van Riel <riel@...hat.com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Tony Lindgren <tony@...mide.com>, Linux USB Mailing List <linux-usb@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, <josh@...htriplett.org>, Rabin Vincent <rabin@....in>, Alan Stern <stern@...land.harvard.edu>, Johannes Weiner <hannes@...xchg.org>, Sasha Levin <sasha.levin@...cle.com>, Andrew Morton <akpm@...ux-foundation.org>, Linux OMAP Mailing List <linux-omap@...r.kernel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Linux ARM Kernel Mailing List <linux-arm-kernel@...ts.infradead.org> Subject: Re: RCU bug with v3.17-rc3 ? On 10/10/2014 11:25 AM, Russell King - ARM Linux wrote: > > Right, so GCC 4.8.{1,2} are totally unsuitable for kernel building (and > it seems that this has been known about for some time.) Looking at http://gcc.gnu.org/PR58854 it seems that all 4.8.x for x < 3 are affected, as well as 4.9.0. > We can blacklist these GCC versions quite easily. We already have GCC > 3.3 blacklisted, and it's trivial to add others. I would want to include > some proper details about the bug, just like the other existing entries > we already have in asm-offsets.c, where we name the functions that the > compiler is known to break where appropriate. Before blacklisting anything, it's worth considering that simple version checks would break existing pre-4.8.3 compilers that have been patched for PR58854. It looks like Yocto and Buildroot issued releases with patched 4.8.2 compilers well before the (fixed) 4.8.3 release. I think the most we can reasonably do without breaking some correctly-behaving toolchains is to emit a warning. Hopefully nobody's still using gcc 4.8 from the Linaro 2013.11 toolchain release -- since it's a 4.8.3 prerelease from before the fix was committed you'll get GCC_VERSION == 40803 but still generate bad code. > However, I'm rather annoyed that there are people here who have known > for some time that GCC 4.8.1 and GCC 4.8.2 _can_ lead to filesystem > corruption, and have sat on their backsides doing nothing about getting > it blacklisted for something like a year. Mea culpa, although I hadn't drawn the connection to FS corruption reports until now. I have known about the issue for some time, but figured the prevalence of the fix in downstream projects largely mitigated the issue. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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