On Tue, Oct 27, 2020 at 1:32 PM Arvind Sankar <nivedita@xxxxxxxxxxxx> wrote:
>
> On Tue, Oct 27, 2020 at 01:28:02PM -0700, Nick Desaulniers wrote:
> > > commit 3193c0836f203a91bef96d88c64cccf0be090d9c
> > > Author: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> > > Date: Wed Jul 17 20:36:45 2019 -0500
> > >
> > > bpf: Disable GCC -fgcse optimization for ___bpf_prog_run()
> > >
> > > has
> > >
> > > Fixes: e55a73251da3 ("bpf: Fix ORC unwinding in non-JIT BPF code")
> > >
> > > and mentions objtool and CONFIG_RETPOLINE.
> >
> > Thanks for the context. It might be time to revisit the above commit.
> > If I revert it (small conflict that's easy to fixup),
> > kernel/bpf/core.o builds cleanly with defconfig+GCC-9.3, so maybe
> > obtool did get smart enough to handle that case? Probably regresses
> > the performance of that main dispatch loop for BPF, but not sure what
> > folks are expecting when retpolines are enabled.
> > --
> > Thanks,
> > ~Nick Desaulniers
>
> The objtool issue was with RETPOLINE disabled.
Ah, sorry, in that case default-CONFIG_RETPOLINE+gcc-9.3:
kernel/bpf/core.o: warning: objtool: ___bpf_prog_run()+0x8d4: sibling
call from callable instruction with modified stack frame
--
Thanks,
~Nick Desaulniers
