On Fri, Mar 16, 2018 at 3:31 PM, Mark Rutland <mark.rutland@xxxxxxx> wrote: > On Fri, Mar 16, 2018 at 02:13:14PM +0000, Mark Rutland wrote: >> On Fri, Mar 16, 2018 at 02:49:00PM +0100, Andrey Konovalov wrote: >> > Hi! >> >> Hi, >> >> > I've recently tried to boot clang built kernel on real hardware >> > (Odroid C2 board) instead of using a VM. The issue that I stumbled >> > upon is that arm64 kvm built with clang doesn't boot. >> > >> > Adding -fno-jump-tables compiler flag to arch/arm64/kvm/* helps. There >> > was a patch some time ago that did exactly that >> > (https://patchwork.kernel.org/patch/10060381/), but it wasn't accepted >> > AFAICT (see the discussion on that thread). >> > >> > What would be the best way to get this fixed? >> >> I think that patch is our best bet currently, but to save ourselves pain >> in future it would be *really* nice if GCC and clang could provide an >> option line -fno-absolute-addressing that would implicitly disable any >> feature that would generate an absolute address as jump tables do. >> >> > I've also had to disable CONFIG_JUMP_LABEL to get the kernel boot >> > (even without kvm enabled), but that might be a different (though >> > related) issue. >> >> With v4.15 (and clang 5.0.0), I did not have to disable jump labels to >> get a kernel booting on a Juno platform, though I did have to pass >> -fno-jump-tables to the hyp code. > > FWIW, with that same compiler and patch applied atop of v4.16-rc4, and > some bodges around clang not liking the rX register naming in the SMCCC > code, I get a kernel that boots on my Juno, though I immediately hit a > KASAN splat: > > [ 8.476766] ================================================================== > [ 8.483990] BUG: KASAN: slab-out-of-bounds in __d_lookup_rcu+0x350/0x400 > [ 8.490664] Read of size 8 at addr ffff8009336e2a30 by task init/1 Hi Mark! Just FYI, this should be fixed with https://reviews.llvm.org/D44981 + https://patchwork.kernel.org/patch/10339103/ Thanks! _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
