On Wed, Apr 6, 2022 at 3:46 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Tue, Apr 05, 2022 at 09:58:28AM -0700, Alexei Starovoitov wrote:
> > On Tue, Apr 5, 2022 at 12:55 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > >
> > >
> > > Clang can inline emit_indirect_jump() and then folds constants, which
> > > results in:
> > >
> > > | vmlinux.o: warning: objtool: emit_bpf_dispatcher()+0x6a4: relocation to !ENDBR: .text.__x86.indirect_thunk+0x40
> > > | vmlinux.o: warning: objtool: emit_bpf_dispatcher()+0x67d: relocation to !ENDBR: .text.__x86.indirect_thunk+0x40
> > > | vmlinux.o: warning: objtool: emit_bpf_tail_call_indirect()+0x386: relocation to !ENDBR: .text.__x86.indirect_thunk+0x20
> > > | vmlinux.o: warning: objtool: emit_bpf_tail_call_indirect()+0x35d: relocation to !ENDBR: .text.__x86.indirect_thunk+0x20
> > >
> > > Suppress the optimization such that it must emit a code reference to
> > > the __x86_indirect_thunk_array[] base.
> > >
> > > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> > > ---
> > > arch/x86/net/bpf_jit_comp.c | 1 +
> > > 1 file changed, 1 insertion(+)
> > >
> > > --- a/arch/x86/net/bpf_jit_comp.c
> > > +++ b/arch/x86/net/bpf_jit_comp.c
> > > @@ -412,6 +412,7 @@ static void emit_indirect_jump(u8 **ppro
> > > EMIT_LFENCE();
> > > EMIT2(0xFF, 0xE0 + reg);
> > > } else if (cpu_feature_enabled(X86_FEATURE_RETPOLINE)) {
> > > + OPTIMIZER_HIDE_VAR(reg);
> > > emit_jump(&prog, &__x86_indirect_thunk_array[reg], ip);
> > > } else
> > > #endif
> >
> > Looks good. Please cc bpf@vger and all bpf maintainers in the future.
>
> Oh right, I'll go add an alias for that.
>
> > We can take it through the bpf tree if you prefer.
>
> I'll take it through the x86/urgent tree if you don't mind.
Sure. Then pls add:
Acked-by: Alexei Starovoitov <ast@xxxxxxxxxx>
