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Date: Wed, 9 Jun 2021 08:56:04 -0700 From: Nathan Chancellor <nathan@...nel.org> To: Peter Zijlstra <peterz@...radead.org>, Lukasz Majczak <lma@...ihalf.com> Cc: Nick Desaulniers <ndesaulniers@...gle.com>, Fāng-ruì Sòng <maskray@...gle.com>, Josh Poimboeuf <jpoimboe@...hat.com>, Guenter Roeck <groeck@...gle.com>, Juergen Gross <jgross@...e.com>, Łukasz Bartosik <lb@...ihalf.com>, LKML <linux-kernel@...r.kernel.org>, mbenes@...e.com, Radosław Biernacki <rad@...ihalf.com>, upstream@...ihalf.com, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>, clang-built-linux <clang-built-linux@...glegroups.com>, Sami Tolvanen <samitolvanen@...gle.com> Subject: Re: [PATCH v3 16/16] objtool,x86: Rewrite retpoline thunk calls On 6/9/2021 8:08 AM, Peter Zijlstra wrote: > On Wed, Jun 09, 2021 at 02:23:28PM +0200, Lukasz Majczak wrote: >> śr., 9 cze 2021 o 09:20 Peter Zijlstra <peterz@...radead.org> napisał(a): >>> >>> On Wed, Jun 09, 2021 at 09:11:18AM +0200, Lukasz Majczak wrote: >>> >>>> I'm sorry I was on vacation last week - do you still need the requested debugs? >>> >>> If the patch here: >>> >>> https://lkml.kernel.org/r/YL3q1qFO9QIRL/BA@hirez.programming.kicks-ass.net >>> >>> does not fix things for you (don't think it actually will), then yes, >>> please send me the information requested. >> >> Ok, it didn't help. Peter, Josh I have sent you a private email with >> requested information. > > OK, I think I've found it. Check this one: > > 5d5: 0f 85 00 00 00 00 jne 5db <cpuidle_reflect+0x22> 5d7: R_X86_64_PLT32 __x86_indirect_thunk_r11-0x4 > > > +Relocation section '.rela.altinstructions' at offset 0 contains 14 entries: > + Offset Info Type Symbol's Value Symbol's Name + Addend > > +0000000000000018 0000000200000002 R_X86_64_PC32 0000000000000000 .text + 5d5 > +000000000000001c 0000009200000002 R_X86_64_PC32 0000000000000000 __x86_indirect_alt_call_r11 + 0 > > Apparently we get conditional branches to retpoline thunks and objtool > completely messes that up. I'm betting this also explains the problems > Nathan is having. Yes, the below patch gets my kernel back to booting so it seems the root cause is the same. > *groan*,.. not sure what to do about this, except return to having > objtool generate code, which everybody hated on. For now I'll make it > skip the conditional branches. > > I wonder if the compiler will also generate conditional tail calls, and > what that does with static_call... now I have to check all that. > > --- Tested-by: Nathan Chancellor <nathan@...nel.org> > diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c > index 24295d39713b..523aa4157f80 100644 > --- a/tools/objtool/arch/x86/decode.c > +++ b/tools/objtool/arch/x86/decode.c > @@ -747,6 +747,10 @@ int arch_rewrite_retpolines(struct objtool_file *file) > > list_for_each_entry(insn, &file->retpoline_call_list, call_node) { > > + if (insn->type != INSN_JUMP_DYNAMIC && > + insn->type != INSN_CALL_DYNAMIC) > + continue; > + > if (!strcmp(insn->sec->name, ".text.__x86.indirect_thunk")) > continue; > >
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