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From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Sami Tolvanen <samitolvanen@google.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Will Deacon <will@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	clang-built-linux@googlegroups.com,
	kernel-hardening@lists.openwall.com, linux-arch@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-pci@vger.kernel.org, x86@kernel.org,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	mhelsley@vmware.com
Subject: Re: [RFC][PATCH] objtool,x86_64: Replace recordmcount with objtool
Date: Wed, 22 Jul 2020 13:55:42 -0400
Message-ID: <20200722135542.41127cc4@oasis.local.home> (raw)
In-Reply-To: <20200626112931.GF4817@hirez.programming.kicks-ass.net>

On Fri, 26 Jun 2020 13:29:31 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> On Thu, Jun 25, 2020 at 03:40:42PM -0700, Sami Tolvanen wrote:
> 
> > > Not boot tested, but it generates the required sections and they look
> > > more or less as expected, ymmv.  
> 
> > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > > index a291823f3f26..189575c12434 100644
> > > --- a/arch/x86/Kconfig
> > > +++ b/arch/x86/Kconfig
> > > @@ -174,7 +174,6 @@ config X86
> > >  	select HAVE_EXIT_THREAD
> > >  	select HAVE_FAST_GUP
> > >  	select HAVE_FENTRY			if X86_64 || DYNAMIC_FTRACE
> > > -	select HAVE_FTRACE_MCOUNT_RECORD
> > >  	select HAVE_FUNCTION_GRAPH_TRACER
> > >  	select HAVE_FUNCTION_TRACER
> > >  	select HAVE_GCC_PLUGINS  
> > 
> > This breaks DYNAMIC_FTRACE according to kernel/trace/ftrace.c:
> > 
> >   #ifndef CONFIG_FTRACE_MCOUNT_RECORD
> >   # error Dynamic ftrace depends on MCOUNT_RECORD
> >   #endif
> > 
> > And the build errors after that seem to confirm this. It looks like we might
> > need another flag to skip recordmcount.  
> 
> Hurm, Steve, how you want to do that?

That was added when we removed that dangerous daemon that did the
updates, and was added to make sure it didn't come back.

We can probably just get rid of it.


> 
> > Anyway, since objtool is run before recordmcount, I just left this unchanged
> > for testing and ignored the recordmcount warnings about __mcount_loc already
> > existing. Something is a bit off still though, I see this at boot:
> > 
> >   ------------[ ftrace bug ]------------
> >   ftrace failed to modify
> >   [<ffffffff81000660>] __tracepoint_iter_initcall_level+0x0/0x40
> >    actual:   0f:1f:44:00:00
> >   Initializing ftrace call sites
> >   ftrace record flags: 0
> >    (0)
> >    expected tramp: ffffffff81056500
> >   ------------[ cut here ]------------
> > 
> > Otherwise, this looks pretty good.  
> 
> Ha! it is trying to convert the "CALL __fentry__" into a NOP and not
> finding the CALL -- because objtool already made it a NOP...
> 
> Weird, I thought recordmcount would also write NOPs, it certainly has
> code for that. I suppose we can use CC_USING_NOP_MCOUNT to avoid those,
> but I'd rather Steve explain this before I wreck things further.

The reason for not having recordmcount insert all the nops, is because
x86 has more than one optimal nop which is determined by the machine it
runs on, and not at compile time. So we figured just updated it then.

We can change it to be a nop on boot, and just modify it if it's not
the optimal nop already. 

That said, Andi Kleen added an option to gcc called -mnop-mcount which
will have gcc do both create the mcount section and convert the calls
into nops. When doing so, it defines CC_USING_NOP_MCOUNT which will
tell ftrace to expect the calls to already be converted.

-- Steve

  parent reply index

Thread overview: 207+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-24 20:31 [PATCH 00/22] add support for Clang LTO Sami Tolvanen
2020-06-24 20:31 ` [PATCH 01/22] objtool: use sh_info to find the base for .rela sections Sami Tolvanen
2020-06-24 20:31 ` [PATCH 02/22] kbuild: add support for Clang LTO Sami Tolvanen
2020-06-24 20:53   ` Nick Desaulniers
2020-06-24 21:29     ` Sami Tolvanen
2020-06-25  2:26   ` Nathan Chancellor
2020-06-25 16:13     ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 03/22] kbuild: lto: fix module versioning Sami Tolvanen
2020-06-24 20:31 ` [PATCH 04/22] kbuild: lto: fix recordmcount Sami Tolvanen
2020-06-24 21:27   ` Peter Zijlstra
2020-06-24 21:45     ` Sami Tolvanen
2020-06-25  7:45       ` Peter Zijlstra
2020-06-25 16:15         ` Sami Tolvanen
2020-06-25 20:02           ` [RFC][PATCH] objtool,x86_64: Replace recordmcount with objtool Peter Zijlstra
2020-06-25 20:54             ` Nick Desaulniers
2020-06-25 22:40             ` Sami Tolvanen
2020-06-26 11:29               ` Peter Zijlstra
2020-06-26 11:42                 ` Peter Zijlstra
2020-07-17 17:28                 ` Sami Tolvanen
2020-07-17 17:36                   ` Steven Rostedt
2020-07-17 17:47                     ` Sami Tolvanen
2020-07-17 18:05                       ` Steven Rostedt
2020-07-20 16:52                         ` Sami Tolvanen
2020-07-22 17:58                           ` Steven Rostedt
2020-07-22 18:07                             ` Sami Tolvanen
2020-07-22 17:55                 ` Steven Rostedt [this message]
2020-07-22 18:41                   ` Peter Zijlstra
2020-07-22 19:09                     ` Steven Rostedt
2020-07-22 20:03                       ` Sami Tolvanen
2020-07-22 23:56                       ` Peter Zijlstra
2020-07-23  0:06                         ` Steven Rostedt
2020-08-06 22:09                           ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 05/22] kbuild: lto: postpone objtool Sami Tolvanen
2020-06-24 21:19   ` Peter Zijlstra
2020-06-24 21:49     ` Sami Tolvanen
2020-06-25  7:47       ` Peter Zijlstra
2020-06-25 16:22         ` Sami Tolvanen
2020-06-25 18:33           ` Peter Zijlstra
2020-06-25 19:32             ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 06/22] kbuild: lto: limit inlining Sami Tolvanen
2020-06-24 21:20   ` Peter Zijlstra
2020-06-24 23:37     ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 07/22] kbuild: lto: merge module sections Sami Tolvanen
2020-06-24 21:01   ` Nick Desaulniers
2020-06-24 21:31     ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 08/22] kbuild: lto: remove duplicate dependencies from .mod files Sami Tolvanen
2020-06-24 21:13   ` Nick Desaulniers
2020-06-24 20:31 ` [PATCH 09/22] init: lto: ensure initcall ordering Sami Tolvanen
2020-06-24 20:31 ` [PATCH 10/22] init: lto: fix PREL32 relocations Sami Tolvanen
2020-06-24 20:31 ` [PATCH 11/22] pci: " Sami Tolvanen
2020-07-17 20:26   ` Bjorn Helgaas
2020-07-22 18:15     ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 12/22] modpost: lto: strip .lto from module names Sami Tolvanen
2020-06-24 22:05   ` Nick Desaulniers
2020-06-24 20:31 ` [PATCH 13/22] scripts/mod: disable LTO for empty.c Sami Tolvanen
2020-06-24 20:57   ` Nick Desaulniers
2020-06-24 20:31 ` [PATCH 14/22] efi/libstub: disable LTO Sami Tolvanen
2020-06-24 20:31 ` [PATCH 15/22] drivers/misc/lkdtm: disable LTO for rodata.o Sami Tolvanen
2020-06-24 20:31 ` [PATCH 16/22] arm64: export CC_USING_PATCHABLE_FUNCTION_ENTRY Sami Tolvanen
2020-06-24 20:31 ` [PATCH 17/22] arm64: vdso: disable LTO Sami Tolvanen
2020-06-24 20:58   ` Nick Desaulniers
2020-06-24 21:09     ` Nick Desaulniers
2020-06-24 23:51       ` Andi Kleen
2020-06-24 21:52     ` Sami Tolvanen
2020-06-24 23:05       ` Nick Desaulniers
2020-06-24 23:39         ` Sami Tolvanen
2020-06-24 20:31 ` [PATCH 18/22] arm64: allow LTO_CLANG and THINLTO to be selected Sami Tolvanen
2020-06-24 20:31 ` [PATCH 19/22] x86, vdso: disable LTO only for vDSO Sami Tolvanen
2020-06-24 20:31 ` [PATCH 20/22] x86, ftrace: disable recordmcount for ftrace_make_nop Sami Tolvanen
2020-06-24 20:31 ` [PATCH 21/22] x86, relocs: Ignore L4_PAGE_OFFSET relocations Sami Tolvanen
2020-06-24 20:32 ` [PATCH 22/22] x86, build: allow LTO_CLANG and THINLTO to be selected Sami Tolvanen
2020-06-24 21:15 ` [PATCH 00/22] add support for Clang LTO Peter Zijlstra
2020-06-24 21:30   ` Sami Tolvanen
2020-06-25  8:27     ` Will Deacon
2020-06-24 21:31   ` Nick Desaulniers
2020-06-25  8:03     ` Peter Zijlstra
2020-06-25  8:24       ` Peter Zijlstra
2020-06-25  8:57         ` Peter Zijlstra
2020-06-30 19:19           ` Marco Elver
2020-06-30 20:12             ` Peter Zijlstra
2020-06-30 20:30               ` Paul E. McKenney
2020-07-01  9:10                 ` Peter Zijlstra
2020-07-01 14:20                   ` David Laight
2020-07-01 16:06                     ` Paul E. McKenney
2020-07-02  9:37                       ` David Laight
2020-07-02 18:00                         ` Paul E. McKenney
2020-07-01  9:41                 ` Marco Elver
2020-07-01 10:03                   ` Will Deacon
2020-07-01 11:40                   ` Peter Zijlstra
2020-07-01 14:06                     ` Paul E. McKenney
2020-07-01 15:05                       ` Peter Zijlstra
2020-07-01 16:03                         ` Paul E. McKenney
2020-07-02  8:20                           ` Peter Zijlstra
2020-07-02 17:59                             ` Paul E. McKenney
2020-07-03 13:13                               ` Peter Zijlstra
2020-07-03 13:25                                 ` Peter Zijlstra
2020-07-03 14:51                                   ` Paul E. McKenney
2020-07-03 14:42                                 ` Paul E. McKenney
2020-07-06 16:26                                   ` Paul E. McKenney
2020-07-06 18:29                                     ` Peter Zijlstra
2020-07-06 18:39                                       ` Paul E. McKenney
2020-07-06 19:40                                         ` Peter Zijlstra
2020-07-06 23:41                                           ` Paul E. McKenney
2020-06-28 16:56 ` Masahiro Yamada
2020-06-29 23:20   ` Sami Tolvanen
2020-07-07 15:51     ` Sami Tolvanen
2020-07-07 16:05       ` Sami Tolvanen
2020-07-07 16:56         ` Jakub Kicinski
2020-07-07 17:17           ` Nick Desaulniers
2020-07-07 17:30             ` Jakub Kicinski
2020-07-11 16:32 ` Paul Menzel
2020-07-12  8:59   ` Sedat Dilek
2020-07-12 18:40     ` Nathan Chancellor
2020-07-14  9:44       ` Sedat Dilek
2020-07-14 17:54         ` Nick Desaulniers
2020-07-12 23:34   ` Sami Tolvanen
2020-07-14 12:16     ` Paul Menzel
2020-07-14 12:35       ` Sedat Dilek
2020-09-03 20:30 ` [PATCH v2 00/28] Add " Sami Tolvanen
2020-09-03 20:30   ` [PATCH v2 01/28] x86/boot/compressed: Disable relocation relaxation Sami Tolvanen
2020-09-03 21:44     ` Kees Cook
2020-09-03 23:42       ` Arvind Sankar
2020-09-04  7:14         ` Nathan Chancellor
2020-09-03 20:30   ` [PATCH v2 02/28] x86/asm: Replace __force_order with memory clobber Sami Tolvanen
2020-09-03 21:45     ` Kees Cook
2020-09-03 20:30   ` [PATCH v2 03/28] lib/string.c: implement stpcpy Sami Tolvanen
2020-09-03 21:47     ` Kees Cook
2020-09-03 20:30   ` [PATCH v2 04/28] RAS/CEC: Fix cec_init() prototype Sami Tolvanen
2020-09-03 21:50     ` Kees Cook
2020-09-03 20:30   ` [PATCH v2 05/28] objtool: Add a pass for generating __mcount_loc Sami Tolvanen
2020-09-03 21:51     ` Kees Cook
2020-09-03 22:03       ` Sami Tolvanen
2020-09-04  9:31         ` peterz
2020-09-10 18:29           ` Kees Cook
2020-09-03 20:30   ` [PATCH v2 06/28] objtool: Don't autodetect vmlinux.o Sami Tolvanen
2020-09-03 21:52     ` Kees Cook
2020-09-03 20:30   ` [PATCH v2 07/28] kbuild: add support for objtool mcount Sami Tolvanen
2020-09-03 21:56     ` Kees Cook
2020-09-03 20:30   ` [PATCH v2 08/28] x86, build: use " Sami Tolvanen
2020-09-03 21:58     ` Kees Cook
2020-09-03 22:11       ` Sami Tolvanen
2020-09-03 20:30   ` [PATCH v2 09/28] kbuild: add support for Clang LTO Sami Tolvanen
2020-09-03 22:08     ` Kees Cook
2020-09-08 17:02       ` Sami Tolvanen
2020-09-05 19:36     ` Masahiro Yamada
2020-09-08 17:10       ` Sami Tolvanen
2020-09-05 20:17     ` Masahiro Yamada
2020-09-08 17:14       ` Sami Tolvanen
2020-09-07 15:30     ` Masahiro Yamada
2020-09-08 17:30       ` Sami Tolvanen
2020-09-03 20:30   ` [PATCH v2 10/28] kbuild: lto: fix module versioning Sami Tolvanen
2020-09-03 22:11     ` Kees Cook
2020-09-08 18:23       ` Sami Tolvanen
2020-09-03 20:30   ` [PATCH v2 11/28] kbuild: lto: postpone objtool Sami Tolvanen
2020-09-03 22:19     ` Kees Cook
2020-09-08 20:56       ` Sami Tolvanen
2020-09-03 20:30   ` [PATCH v2 12/28] kbuild: lto: limit inlining Sami Tolvanen
2020-09-03 22:20     ` Kees Cook
2020-09-03 20:30   ` [PATCH v2 13/28] kbuild: lto: merge module sections Sami Tolvanen
2020-09-03 22:23     ` Kees Cook
2020-09-07 15:25     ` Masahiro Yamada
2020-09-08 21:07       ` Sami Tolvanen
2020-09-03 20:30   ` [PATCH v2 14/28] kbuild: lto: remove duplicate dependencies from .mod files Sami Tolvanen
2020-09-03 22:29     ` Kees Cook
2020-09-03 20:30   ` [PATCH v2 15/28] init: lto: ensure initcall ordering Sami Tolvanen
2020-09-03 22:40     ` Kees Cook
2020-09-08 21:16       ` Sami Tolvanen
2020-09-10  9:25     ` David Woodhouse
2020-09-10 15:07       ` Sami Tolvanen
2020-09-03 20:30   ` [PATCH v2 16/28] init: lto: fix PREL32 relocations Sami Tolvanen
2020-09-03 22:41     ` Kees Cook
2020-09-03 20:30   ` [PATCH v2 17/28] PCI: Fix PREL32 relocations for LTO Sami Tolvanen
2020-09-03 22:42     ` Kees Cook
2020-09-03 20:30   ` [PATCH v2 18/28] modpost: lto: strip .lto from module names Sami Tolvanen
2020-09-03 22:42     ` Kees Cook
2020-09-03 20:30   ` [PATCH v2 19/28] scripts/mod: disable LTO for empty.c Sami Tolvanen
2020-09-03 22:43     ` Kees Cook
2020-09-03 20:30   ` [PATCH v2 20/28] efi/libstub: disable LTO Sami Tolvanen
2020-09-03 22:43     ` Kees Cook
2020-09-03 20:30   ` [PATCH v2 21/28] drivers/misc/lkdtm: disable LTO for rodata.o Sami Tolvanen
2020-09-03 20:30   ` [PATCH v2 22/28] arm64: export CC_USING_PATCHABLE_FUNCTION_ENTRY Sami Tolvanen
2020-09-03 22:44     ` Kees Cook
2020-09-08 21:23       ` Sami Tolvanen
2020-09-03 20:30   ` [PATCH v2 23/28] arm64: vdso: disable LTO Sami Tolvanen
2020-09-03 22:45     ` Kees Cook
2020-09-03 20:30   ` [PATCH v2 24/28] KVM: arm64: disable LTO for the nVHE directory Sami Tolvanen
2020-09-03 22:45     ` Kees Cook
2020-09-03 20:30   ` [PATCH v2 25/28] arm64: allow LTO_CLANG and THINLTO to be selected Sami Tolvanen
2020-09-03 22:45     ` Kees Cook
2020-09-03 20:30   ` [PATCH v2 26/28] x86, vdso: disable LTO only for vDSO Sami Tolvanen
2020-09-03 22:46     ` Kees Cook
2020-09-03 20:30   ` [PATCH v2 27/28] x86, relocs: Ignore L4_PAGE_OFFSET relocations Sami Tolvanen
2020-09-03 22:47     ` Kees Cook
2020-09-08 23:28       ` Sami Tolvanen
2020-09-03 20:30   ` [PATCH v2 28/28] x86, build: allow LTO_CLANG and THINLTO to be selected Sami Tolvanen
2020-09-03 22:48     ` Kees Cook
2020-09-03 23:34   ` [PATCH v2 00/28] Add support for Clang LTO Kees Cook
2020-09-04  4:45     ` Nathan Chancellor
2020-09-03 23:38   ` Kees Cook
2020-09-04  7:53   ` Sedat Dilek
2020-09-04  8:55   ` peterz
2020-09-04  9:08     ` Sedat Dilek
2020-09-06  0:24   ` Masahiro Yamada
2020-09-08 23:46     ` Sami Tolvanen
2020-09-10  1:18       ` Masahiro Yamada
2020-09-10 15:17         ` Sami Tolvanen
2020-09-10 18:18         ` Kees Cook

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