On Wed, 20 May 2020 at 05:44, Nathan Chancellor <natechancel...@gmail.com> wrote: > > On Tue, May 19, 2020 at 11:16:24PM -0400, Qian Cai wrote: > > On Tue, May 19, 2020 at 10:47 PM Nathan Chancellor > > <natechancel...@gmail.com> wrote: > > > > > > On Tue, May 19, 2020 at 10:28:41PM -0400, Qian Cai wrote: > > > > > > > > > > > > > On May 19, 2020, at 6:05 PM, Thomas Gleixner <t...@linutronix.de> > > > > > wrote: > > > > > > > > > > Yes, it's unfortunate, but we have to stop making major concessions > > > > > just > > > > > because tools are not up to the task. > > > > > > > > > > We've done that way too much in the past and this particular problem > > > > > clearly demonstrates that there are limits. > > > > > > > > > > Making brand new technology depend on sane tools is not asked too > > > > > much. And yes, it's inconvenient, but all of us have to build tools > > > > > every now and then to get our job done. It's not the end of the world. > > > > > > > > > > Building clang is trivial enough and pointing the make to the right > > > > > compiler is not rocket science either. > > > > > > > > Yes, it all make sense from that angle. On the other hand, I want to be > > > > focus on kernel rather than compilers by using a stable and > > > > rocket-solid version. Not mentioned the time lost by compiling and > > > > properly manage my own toolchain in an automated environment, using > > > > such new version of compilers means that I have to inevitably deal with > > > > compiler bugs occasionally. Anyway, it is just some other more bugs I > > > > have to deal with, and I don’t have a better solution to offer right > > > > now. > > > > > > Hi Qian, > > > > > > Shameless plug but I have made a Python script to efficiently configure > > > then build clang specifically for building the kernel (turn off a lot of > > > different things that the kernel does not need). > > > > > > https://github.com/ClangBuiltLinux/tc-build > > > > > > I added an option '--use-good-revision', which uses an older master > > > version (basically somewhere between clang-10 and current master) that > > > has been qualified against the kernel. I currently update it every > > > Linux release but I am probably going to start doing it every month as > > > I have written a pretty decent framework to ensure that nothing is > > > breaking on either the LLVM or kernel side. > > > > > > $ ./build-llvm.py --use-good-revision > > > > > > should be all you need to get off the ground and running if you wanted > > > to give it a shot. The script is completely self contained by default so > > > it won't mess with the rest of your system. Additionally, leaving off > > > '--use-good-revision' will just use the master branch, which can > > > definitely be broken but not as often as you would think (although I > > > totally understand wanting to focus on kernel regressions only). > > > > Great, thanks. I'll try it in a bit. > > Please let me know if there are any issues! > > Do note that in order to get support for Marco's series, you will need > to have a version of LLVM that includes [1], which the current > --use-good-revision does not. You can checkout that revision exactly > through the '-b' ('--branch') parameter: > > $ ./build-llvm.py -b 5a2c31116f412c3b6888be361137efd705e05814 > > I also see another patch in LLVM that concerns KCSAN [2] but that does > not appear used in Marco's series. Still might be worth having available > in your version of clang. > > I'll try to bump the hash that '--use-good-revision' uses soon. I might > wait until 5.7 final so that I can do both at the same time like I > usually do but we'll see how much time I have. > > [1]: > https://github.com/llvm/llvm-project/commit/5a2c31116f412c3b6888be361137efd705e05814 > [2]: > https://github.com/llvm/llvm-project/commit/151ed6aa38a3ec6c01973b35f684586b6e1c0f7e
Thanks for sharing the script, this is very useful! Note that [2] above is used, but optional: https://lore.kernel.org/lkml/20200515150338.190344-5-el...@google.com/ It's not required for KCSAN to function correctly, but if it's available it'll help find more data races with the default config. Thanks, -- Marco