linux-kernel - Re: [PATCH 00/22] x86, objtool: several fixes/improvements

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Date:   Mon, 15 Jul 2019 14:45:39 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arnd Bergmann <arnd@...db.de>, Jann Horn <jannh@...gle.com>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH 00/22] x86, objtool: several fixes/improvements

On Mon, Jul 15, 2019 at 12:38 PM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>
> On Sun, Jul 14, 2019 at 07:36:55PM -0500, Josh Poimboeuf wrote:
> > There have been a lot of objtool bug reports lately, mainly related to
> > Clang and BPF.  As part of fixing those bugs, I added some improvements
> > to objtool which uncovered yet more bugs (some kernel, some objtool).
> >
> > I've given these patches a lot of testing with both GCC and Clang.  More
> > compile testing of objtool would be appreciated, as the kbuild test
> > robot doesn't seem to be paying much attention to my branches lately.
> >
> > There are still at least three outstanding issues:
> >
> > 1) With clang I see:
> >
> >      drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: .altinstr_replacement+0x88: redundant UACCESS disable

For a defconfig, that's the only issue I see.
(Note that I just landed https://reviews.llvm.org/rL366130 for fixing
up bugs from loop unrolling loops containing asm goto with Clang, so
anyone else testing w/ clang will see fewer objtool warnings with that
patch applied.  A follow up is being worked on in
https://reviews.llvm.org/D64101).

For allmodconfig:
arch/x86/ia32/ia32_signal.o: warning: objtool:
ia32_setup_rt_frame()+0x247: call to memset() with UACCESS enabled
mm/kasan/common.o: warning: objtool: kasan_report()+0x52: call to
__stack_chk_fail() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool:
x32_setup_rt_frame()+0x255: call to memset() with UACCESS enabled
arch/x86/kernel/signal.o: warning: objtool: __setup_rt_frame()+0x254:
call to memset() with UACCESS enabled
drivers/ata/sata_dwc_460ex.o: warning: objtool:
sata_dwc_bmdma_start_by_tag()+0x3a0: can't find switch jump table
lib/ubsan.o: warning: objtool: __ubsan_handle_type_mismatch()+0x88:
call to memset() with UACCESS enabled
lib/ubsan.o: warning: objtool: ubsan_type_mismatch_common()+0x610:
call to __stack_chk_fail() with UACCESS enabled
lib/ubsan.o: warning: objtool: __ubsan_handle_type_mismatch_v1()+0x88:
call to memset() with UACCESS enabled
drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool:
.altinstr_replacement+0x56: redundant UACCESS disable

Without your series, I see them anyways, so I don't consider them
regressions added by this series.  Let's follow up on these maybe in a
new thread?  (Shall I send you these object files?)

So for the series:
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>

> >
> >    I haven't dug into it yet.
> >
> > 2) There's also an issue in clang where a large switch table had a bunch
> >    of unused (bad) entries.  It's not a code correctness issue, but
> >    hopefully it can get fixed in clang anyway.  See patch 20/22 for more
> >    details.

Thanks for the report, let's follow up on steps for me to reproduce.

> > These patches are also at:
> >   git://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git objtool-many-fixes

Are these the same patches? Some of the commit messages look different, like:
https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git/commit/?h=objtool-many-fixes&id=3e39561c52c4f0062207d604c972148b7b60c341


--
Thanks,
~Nick Desaulniers