Messages in this thread | | | Date | Wed, 6 May 2020 08:31:56 -0700 | From | Nathan Chancellor <> | Subject | Re: [PATCH] arm64: disable patchable function entry on big-endian clang builds |
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On Wed, May 06, 2020 at 12:22:58PM +0200, Arnd Bergmann wrote: > On Wed, May 6, 2020 at 5:45 AM Nathan Chancellor > <natechancellor@gmail.com> wrote: > > On Tue, May 05, 2020 at 07:42:43PM +0200, Torsten Duwe wrote: > > > On Tue, 5 May 2020 15:25:56 +0100 Mark Rutland <mark.rutland@arm.com> wrote: > > > > On Tue, May 05, 2020 at 04:12:36PM +0200, Arnd Bergmann wrote: > > > > This practically rules out a BE distro kernel with things like PAC, > > > > which isn't ideal. > > > > To be fair, are there big endian AArch64 distros? > > > > https://wiki.debian.org/Arm64Port: "There is also a big-endian version > > of the architecture/ABI: aarch64_be-linux-gnu but we're not supporting > > that in Debian (so there is no corresponding Debian architecture name) > > and hopefully will never have to. Nevertheless you might want to check > > for this by way of completeness in upstream code." > > > > OpenSUSE and Fedora don't appear to have support for big endian. > > I don't think any of the binary distros ship big endian ARM64. There are > a couple of users that tend to build everything from source using Yocto > or similar embedded distros, but as far as I can tell this is getting less > common over time as applications get ported to be compatible with > big-endian, or get phased out and replaced by code running on regular > little-endian systems. > > The users we see today are likely in telco, military or aerospace > settings (While earth is mostly little-endian these days, space is > definitely big-endian) that got ported from big-endian hardware, but > often with a high degree of customization and long service life.
Ah yes, that makes sense, thanks for the information and background. Helps orient myself for the future.
> My policy for Arm specific kernel code submissions is generally that > it should be written so it can work on either big-endian or little-endian > using the available abstractions (just like any architecture independent > code), but I don't normally expect it to be tested on big endian. > > There are some important examples of code that just doesn't work > on big-endian because it's far too hard, e.g. the UEFI runtime services. > That is also ok, if anyone really needs it, they can do the work. > > > > I suggest to get a quote from clang folks first about their schedule and > > > regarded importance of patchable-function-entries on BE, and leave it as > > > is: broken on certain clang configurations. It's not the kernel's fault. > > > > We can file an upstream PR (https://bugs.llvm.org) to talk about this > > (although I've CC'd Fangrui) but you would rather the kernel fail to > > work properly than prevent the user from being able to select that > > option? Why even have the "select" or "depends on" keyword then? > > I definitely want all randconfig kernels to build without warnings, > and I agree with you that making it just fail at build time is not > a good solution. > > > That said, I do think we should hold off on this patch until we hear > > from the LLVM developers. > > +1 > > Arnd
Glad we are on the same page.
Cheers, Nathan
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