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

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Message-ID: <CAKwvOd=tRwOvLdQXDRYo00P3vLAnwnb1SXtaHPVkXTnfjMst+g@mail.gmail.com>
Date:   Tue, 19 Jan 2021 13:29:16 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Josh Poimboeuf <jpoimboe@...hat.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 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.

> > 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
>
> > 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
>
> --
> Josh
>


-- 
Thanks,
~Nick Desaulniers