From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0A7F3C43331 for ; Wed, 1 Apr 2020 14:14:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C8AA4206F8 for ; Wed, 1 Apr 2020 14:14:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="X3JUIwOp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732952AbgDAOOL (ORCPT ); Wed, 1 Apr 2020 10:14:11 -0400 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:50890 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1732928AbgDAOOJ (ORCPT ); Wed, 1 Apr 2020 10:14:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1585750449; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=6fNGqZ5cbqa8gRYbmHJQeoCfCtbovl8FPd5umu3T68A=; b=X3JUIwOpa8t+WJh2TsI2AzYKKwi7pourCLqh1dKnUGDeVddNUviY9uTDkDmLRhO0g5FaGe s5jgL2VKLablw1O8C2Bx4IEAOu09TH3+JAJnoL2lmctxo+24FLDEl9X0Tt2TYqPuFHNLW6 sWhm+IP+TC1XQDXwlO+IR6dJusGiZ+o= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-339-i-0dX9cSM1y9opEE-GbX9g-1; Wed, 01 Apr 2020 10:14:07 -0400 X-MC-Unique: i-0dX9cSM1y9opEE-GbX9g-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 82D2B1088381; Wed, 1 Apr 2020 14:14:05 +0000 (UTC) Received: from treble (ovpn-118-135.phx2.redhat.com [10.3.118.135]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A094496F83; Wed, 1 Apr 2020 14:14:04 +0000 (UTC) Date: Wed, 1 Apr 2020 09:14:02 -0500 From: Josh Poimboeuf To: Peter Zijlstra Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org, x86@kernel.org, mhiramat@kernel.org, mbenes@suse.cz, Steven Rostedt Subject: Re: [PATCH v2] objtool,ftrace: Implement UNWIND_HINT_RET_OFFSET Message-ID: <20200401141402.m4klvezp5futb7ff@treble> References: <20200327010001.i3kebxb4um422ycb@treble> <20200330170200.GU20713@hirez.programming.kicks-ass.net> <20200330190205.k5ssixd5hpshpjjq@treble> <20200330200254.GV20713@hirez.programming.kicks-ass.net> <20200331111652.GH20760@hirez.programming.kicks-ass.net> <20200331202315.zialorhlxmml6ec7@treble> <20200331204047.GF2452@worktop.programming.kicks-ass.net> <20200331211755.pb7f3wa6oxzjnswc@treble> <20200331212040.7lrzmj7tbbx2jgrj@treble> <20200331222703.GH2452@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200331222703.GH2452@worktop.programming.kicks-ass.net> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 01, 2020 at 12:27:03AM +0200, Peter Zijlstra wrote: > On Tue, Mar 31, 2020 at 04:20:40PM -0500, Josh Poimboeuf wrote: > > On Tue, Mar 31, 2020 at 04:17:58PM -0500, Josh Poimboeuf wrote: > > > > I'm not against adding a second/separate hint for this. In fact, I > > > > almost considered teaching objtool how to interpret the whole IRET frame > > > > so that we can do it without hints. It's just that that's too much code > > > > for this one case. > > > > > > > > HINT_IRET_SELF ? > > > > > > Despite my earlier complaint about stack size knowledge, we could just > > > forget the hint and make "iretq in C code" equivalent to "reduce stack > > > size by arch_exception_stack_size()" and keep going. There's > > > file->c_file which tells you it's a C file. > > > > Or maybe "iretq in an STT_FUNC" is better since this pattern could > > presumably happen in a callable asm function. > > Like so then? I'd suggest a patch split like: 1) objtool: automagic IRET-in-func 2) objtool: add RET_OFFSET 3) ftrace: re-organize asm (and use RET_OFFSET hint) 4) objtool: remove now-unused SAVE/RESTORE > --- a/arch/x86/include/asm/orc_types.h > +++ b/arch/x86/include/asm/orc_types.h > @@ -58,8 +58,13 @@ > #define ORC_TYPE_CALL 0 > #define ORC_TYPE_REGS 1 > #define ORC_TYPE_REGS_IRET 2 > -#define UNWIND_HINT_TYPE_SAVE 3 > -#define UNWIND_HINT_TYPE_RESTORE 4 > + > +/* > + * RET_OFFSET: Used on instructions that terminate a function; mostly RETURN > + * and sibling calls. On these, sp_offset denotes the expected offset from > + * initial_func_cfi. > + */ > +#define UNWIND_HINT_TYPE_RET_OFFSET 3 I think this comment belongs at the UNWIND_HINT_RET_OFFSET macro definition. > --- a/arch/x86/kernel/ftrace.c > +++ b/arch/x86/kernel/ftrace.c > @@ -282,7 +282,8 @@ static inline void tramp_free(void *tram > > /* Defined as markers to the end of the ftrace default trampolines */ > extern void ftrace_regs_caller_end(void); > -extern void ftrace_epilogue(void); > +extern void ftrace_regs_caller_ret(void); > +extern void ftrace_caller_end(void); > extern void ftrace_caller_op_ptr(void); > extern void ftrace_regs_caller_op_ptr(void); > > @@ -334,7 +335,7 @@ create_trampoline(struct ftrace_ops *ops > call_offset = (unsigned long)ftrace_regs_call; > } else { > start_offset = (unsigned long)ftrace_caller; > - end_offset = (unsigned long)ftrace_epilogue; > + end_offset = (unsigned long)ftrace_caller_end; > op_offset = (unsigned long)ftrace_caller_op_ptr; > call_offset = (unsigned long)ftrace_call; > } > @@ -366,6 +367,13 @@ create_trampoline(struct ftrace_ops *ops > if (WARN_ON(ret < 0)) > goto fail; > > + if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) { > + ip = ftrace_regs_caller_ret; > + ret = probe_kernel_read(ip, (void *)retq, RET_SIZE); > + if (WARN_ON(ret < 0)) > + goto fail; > + } > + Hm? This function creates a trampoline but it looks like this change is overwriting the original ftrace_64 code itself? > --- a/tools/objtool/Makefile > +++ b/tools/objtool/Makefile > @@ -31,7 +31,7 @@ INCLUDES := -I$(srctree)/tools/include \ > -I$(srctree)/tools/arch/$(HOSTARCH)/include/uapi \ > -I$(srctree)/tools/arch/$(SRCARCH)/include > WARNINGS := $(EXTRA_WARNINGS) -Wno-switch-default -Wno-switch-enum -Wno-packed > -CFLAGS := -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -g $(INCLUDES) $(LIBELF_FLAGS) > +CFLAGS := -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -ggdb3 $(INCLUDES) $(LIBELF_FLAGS) > LDFLAGS += $(LIBELF_LIBS) $(LIBSUBCMD) $(KBUILD_HOSTLDFLAGS) Why? Smells like a separate patch at least. -- Josh