On 10/13/2014 10:06 PM, Greg KH wrote: > On Mon, Oct 13, 2014 at 12:43:07PM +0100, Russell King - ARM Linux wrote: >> On Mon, Oct 13, 2014 at 09:11:34AM +0000, David Laight wrote: >>> From: Nathan Lynch >>>> 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. >>> >>> Is it possible to compile a small code fragment and check the generated >>> code for the bug? >>> Possibly predicated on the broken version number to avoid false positives. >> >> I don't see how - it looks like it requires an interrupt to occur at an >> opportune moment to provoke the function to fail. The alternative would >> be to parse the assembly generated by the compiler to determine how it >> is dealing with the stack. >> >> I think the only viable solution here is that: >> >> 1. We blacklist the bad compiler versions outright in the kernel. > > Yes, please do this, it's what we have done for other buggy compiler > versions, no need to do something different here. > >> Remember, it's the distro's choice to fix these buggy compilers, so the >> onus is on _them_ to deal with the mess they've created by doing so. > > I totally agree. > > Is someone going to send this patch, or do I have to write it myself? I did on Friday (arm: Blacklist gcc 4.8.[012] ...) but Russell said he was doing it himself. Regards, Peter Hurley -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html