On Thu, Mar 4, 2021 at 2:34 PM Sami Tolvanen <samitolvanen@xxxxxxxxxx> wrote: > > On Thu, Mar 4, 2021 at 2:17 PM Marc Zyngier <maz@xxxxxxxxxx> wrote: > > > > On Thu, 04 Mar 2021 21:25:41 +0000, > > Sami Tolvanen <samitolvanen@xxxxxxxxxx> wrote: > > > > > > On Thu, Mar 4, 2021 at 11:15 AM Marc Zyngier <maz@xxxxxxxxxx> wrote: > > > > > > > > On Thu, 04 Mar 2021 18:45:44 +0000, > > > > Sami Tolvanen <samitolvanen@xxxxxxxxxx> wrote: > > > > > > > > > > allmodconfig + CONFIG_LTO_CLANG_THIN=y fails to build due to following > > > > > linker errors: > > > > > > > > > > ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21CC): > > > > > > > > I assume this message is only an oddity, right? Because > > > > __guest_enter() is as far as you can imagine from irqbypass.c... > > > > > > I'm not sure what's up with the filename in the error message. Fangrui > > > or Nick probably have a better idea. > > > > > > > > relocation R_AARCH64_CONDBR19 out of range: 2031220 is not in > > > > > [-1048576, 1048575]; references hyp_panic > > > > > >>> defined in vmlinux.o > > > > > > > > > > ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21E0): > > > > > relocation R_AARCH64_ADR_PREL_LO21 out of range: 2031200 is not in > > > > > [-1048576, 1048575]; references hyp_panic > > > > > >>> defined in vmlinux.o > > > > > > > > > > As LTO is not really necessary for the hypervisor code, disable it for > > > > > the hyp directory to fix the build. > > > > > > > > Can you shed some light on what the problem is exactly? > > > > > > I assume hyp_panic() ends up being placed too far from __guest_enter() > > > when the kernel is large enough. Possibly something to do with LLVM > > > always splitting functions into separate sections with LTO. I'm not > > > sure why the linker cannot shuffle things around to make everyone > > > happy in this case, but I confirmed that this patch also fixes the > > > build issue for me: > > > > > > diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c > > > index af8e940d0f03..128197b7c794 100644 > > > --- a/arch/arm64/kvm/hyp/vhe/switch.c > > > +++ b/arch/arm64/kvm/hyp/vhe/switch.c > > > @@ -214,7 +214,7 @@ static void __hyp_call_panic(u64 spsr, u64 elr, u64 par) > > > } > > > NOKPROBE_SYMBOL(__hyp_call_panic); > > > > > > -void __noreturn hyp_panic(void) > > > +void __noreturn hyp_panic(void) __section(".text") > > > { > > > u64 spsr = read_sysreg_el2(SYS_SPSR); > > > u64 elr = read_sysreg_el2(SYS_ELR); > > > > > > > We're getting into black-magic territory here. Why wouldn't hyp_panic > > be in the .text section already? > > It's not quite black magic. LLVM essentially flips on > -ffunction-sections with LTO and therefore, hyp_panic() will be in > .text.hyp_panic in vmlinux.o, while __guest_enter() will be in .text. > Everything ends up in .text when we link vmlinux, of course. > > $ readelf --sections vmlinux.o | grep hyp_panic > [3936] .text.hyp_panic PROGBITS 0000000000000000 004b56e4 Note that disabling LTO here has essentially the same effect as using __section(".text"). It stops the compiler from splitting these functions into .text.* sections and makes it less likely that hyp_panic() ends up too far away from __guest_enter(). If neither of these workarounds sound appealing, I suppose we could alternatively change hyp/entry.S to use adr_l for hyp_panic. Thoughts? Sami _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm