linux-kernel - Re: [PATCH 00/21] objtool: vmlinux.o and CLANG LTO support

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Date:   Wed, 20 Jan 2021 09:37:43 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Sami Tolvanen <samitolvanen@...gle.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Kees Cook <keescook@...omium.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Miroslav Benes <mbenes@...e.cz>
Subject: Re: [PATCH 00/21] objtool: vmlinux.o and CLANG LTO support

On Tue, Jan 19, 2021 at 01:29:16PM -0800, Nick Desaulniers wrote:
> On Mon, Jan 18, 2021 at 9:23 AM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> >
> > On Thu, Jan 14, 2021 at 04:41:28PM -0800, Sami Tolvanen wrote:
> > > I can confirm that all the warnings I previously saw are now fixed,
> > > but I'm seeing a few new ones:
> > >
> > > vmlinux.o: warning: objtool: balance_leaf_when_delete()+0x17d4: stack state mismatch: cfa1=7+192 cfa2=7+176
> > > vmlinux.o: warning: objtool: internal_move_pointers_items()+0x9f7: stack state mismatch: cfa1=7+160 cfa2=7+176
> >
> > These seem legit stack state mismatches (compiler bug).  Two code
> > blocks, with different stack sizes, transfer control to the same
> > noreturn block (violating DWARF/ORC expectation that each instruction
> > has a deterministic stack layout).  In both cases the noreturn block has
> > a call to __reiserfs_panic().
> >
> > https://paste.centos.org/view/081cbfc1
> > https://paste.centos.org/view/265968a6
> >
> 
> Sorry, I think all of the pastes linked here expired before I had a
> chance to grab them.

Attached, balance_leaf_when_delete.txt and internal_move_pointers_items.txt.

> > > vmlinux.o: warning: objtool: strncpy_from_user()+0x181: call to do_strncpy_from_user() with UACCESS enabled
> > > vmlinux.o: warning: objtool: strnlen_user()+0x12b: call to do_strnlen_user() with UACCESS enabled
> >
> > It's odd that Clang wouldn't inline these static single-called
> > functions.  I could '__always_inline' them, but is this expected
> > behavior?
> >
> > > vmlinux.o: warning: objtool: i915_gem_execbuffer2_ioctl()+0x390: call to __ubsan_handle_negate_overflow() with UACCESS enabled
> >
> > PeterZ, have you seen this one?
> >
> > https://paste.centos.org/view/b4723113

Attached, i915_gem_execbuffer2_ioctl.txt.

> >
> > > vmlinux.o: warning: objtool: .text.snd_trident_free_voice: unexpected end of section
> >
> > Another weird compiler issue.  It generates obviously dead code which
> > jumps off the end of the function:
> >
> >   f7:   b0 01                   mov    $0x1,%al
> >   f9:   84 c0                   test   %al,%al
> >   fb:   0f 84 79 05 00 00       je     67a <snd_trident_free_voice+0x67a>
> >
> > https://paste.centos.org/view/a1887ae3

Attached, snd_trident_free_voice.txt.

-- 
Josh

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