On Tue, Jan 03, 2023 at 05:50:00PM +0100, Arnd Bergmann wrote: > On Tue, Jan 3, 2023, at 17:19, Mark Rutland wrote: > > On Tue, Jan 03, 2023 at 02:03:37PM +0000, Mark Rutland wrote: > >> On Tue, Jan 03, 2023 at 01:25:35PM +0000, Mark Rutland wrote: > >> > On Tue, Dec 20, 2022 at 12:08:16PM +0100, Peter Zijlstra wrote: > > >> ... makes GCC much happier: > > > >> ... I'll go check whether clang is happy with that, and how far back that can > >> go, otherwise we'll need to blat the high half with a separate constaint that > >> (ideally) doesn't end up allocating a pointless address register. > > > > Hmm... from the commit history it looks like GCC prior to 5.1 might not be > > happy with that, but that *might* just be if we actually do arithmetic on the > > value, and we might be ok just using it for memroy effects. I can't currently > > get such an old GCC to run on my machines so I haven't been able to check. > > gcc-5.1 is the oldest (barely) supported compiler, the minimum was > last raised from gcc-4.9 in linux-5.15. If only gcc-4.9 and older are > affected, we're good on mainline but may still want a fix for stable > kernels. Yup; I just wanted something that would easily backport to stable, at least as far as linux-4.9.y (where I couldn't find the minimum GCC version when I looked yesterday). > I checked that the cross-compiler binaries from [1] still work, but I noticed > that this version is missing the native aarch64-to-aarch64 compiler (x86 to > aarch64 and vice versa are there), and you need to install libmpfr4 [2] > as a dependency. The newer compilers (6.5.0 and up) don't have these problems. I was trying the old kernel.org crosstool binaries, but I was either missing a library (or I have an incompatible version) on my x86_64 host. I'll have another look today -- thanks for the pointers! Mark. > Arnd > > [1] https://mirrors.edge.kernel.org/pub/tools/crosstool/files/bin/arm64/5.5.0/ > [2] http://ftp.uk.debian.org/debian/pool/main/m/mpfr4/libmpfr4_3.1.5-1_arm64.deb
