On Thu, Feb 23, 2023 at 11:29 AM Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx> wrote: > I didn’t see any place emitting DADDI. Right, the JIT only uses unsigned arithmetics :) > Yes I analysed all other place, most of them are just calculating memory > address offsets and they should never overflow. Other two is doing addition > to zero to load immediate, which should be still fine. Ok. > >> --- a/arch/mips/net/bpf_jit_comp.c > >> +++ b/arch/mips/net/bpf_jit_comp.c > >> @@ -218,9 +218,17 @@ bool valid_alu_i(u8 op, s32 imm) > >> /* All legal eBPF values are valid */ > >> return true; > >> case BPF_ADD: > >> +#ifdef CONFIG_64BIT > > > > DADDI/DADDIU are only available on 64-bit CPUs, so the errata would > > only be applicable to that. No need for the CONFIG_64BIT conditional. > > It’s possible to compile a 32bit kernel for R4000 with CONFIG_CPU_DADDI_WORKAROUNDS > enabled. Yes, but DADDI/DADDIU are 64-bit instructions so they would not be available when compiling the kernel in 32-bit mode for R4000, and hence the workaround would not be applicable, right? If this is correct, I would imagine CONFIG_CPU_DADDI_WORKAROUNDS itself to be conditional on CONFIG_64BIT. That way the this relationship is expressed once in the Kconfig file, instead of being spread out over multiple places in the code.
