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? thanks, greg k-h -- 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