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Date: Wed, 9 Jun 2021 17:08:04 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Lukasz Majczak <lma@...ihalf.com> Cc: Nathan Chancellor <nathan@...nel.org>, 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 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. *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. --- 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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