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 B4284C43331 for ; Wed, 1 Apr 2020 14:39:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8489A20658 for ; Wed, 1 Apr 2020 14:39:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="HJQlZaka" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733105AbgDAOjX (ORCPT ); Wed, 1 Apr 2020 10:39:23 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:36045 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1732976AbgDAOjX (ORCPT ); Wed, 1 Apr 2020 10:39:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1585751962; 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=RpUXP8laC9RyobE1gvL0sU8pGwybPyvUGTH+WRG12+4=; b=HJQlZaka6R/tjs/dKiuiyyg3op/lo+lrA//gRdLufpOEIoYrEe2VVm43RjVIpjoNJBc/R0 KU2fLqhdUeOgpFgI4A7u7pjQU5DlKAoG+YZhoWtBjbVu/nhTCaDDFu4t7raZjBvaMBvBYT lksHjJM/SRAJhF7tNOCKLTSOrok7MN4= 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-128-jU89qjhQPXuRw-w6e6IVkQ-1; Wed, 01 Apr 2020 10:39:21 -0400 X-MC-Unique: jU89qjhQPXuRw-w6e6IVkQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 765DB1005055; Wed, 1 Apr 2020 14:39:19 +0000 (UTC) Received: from treble (ovpn-118-135.phx2.redhat.com [10.3.118.135]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8CEE4D768F; Wed, 1 Apr 2020 14:39:18 +0000 (UTC) Date: Wed, 1 Apr 2020 09:39:16 -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: <20200401143916.h5keq55yabetyv5u@treble> References: <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> <20200401141402.m4klvezp5futb7ff@treble> <20200401142226.GU20696@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200401142226.GU20696@hirez.programming.kicks-ass.net> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 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 04:22:26PM +0200, Peter Zijlstra wrote: > > > --- 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. > > Humph, ok, but there's two of those :/ Just commenting the asm one should be fine I think. That way a reader of code using the macro is more likely to understand its purpose. > > > --- 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? > > Ahh. So if you look at what the trampoline copies, you'll note we'll > copy until -- but *NOT* including -- the jmp ftrace_epilogue. Instead > we'll write a RET at the end. > > However, due to splitting the return path, such that each instruction > has a unique stack offset, we now have a second jmp ftrace_epilogue in > the middle of the function. That too needs to be overwritten by a RET. Right, but 'ip' needs to point to the trampoline's version of 'ftrace_regs_caller_ret', not the original ftrace_64 version. > > > --- 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. > > Oh, whoops :-) I keep doing this every time I need to run gdb on it. > I'll make it go away. Ha, I do something similar, I just add -O0 to CFLAGS. -- Josh