linux-kernel - Re: objtool crashes on clang output (drivers/hwmon/pmbus/adm1275.o)

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Date:   Fri, 12 Jul 2019 09:51:35 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Jann Horn <jannh@...gle.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: objtool crashes on clang output (drivers/hwmon/pmbus/adm1275.o)

On Thu, Jul 11, 2019 at 11:29 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Thu, Jul 11, 2019 at 11:05 PM 'Jann Horn' via Clang Built Linux
> <clang-built-linux@...glegroups.com> wrote:
> > I was playing around with building the kernel with LLVM a few months
> > ago and used this local patch, but didn't get around to submitting
> > upstream because I couldn't reproduce the problem for some reason. I
> > think the warnings you're getting sound like what I saw back then:
> > https://gist.github.com/thejh/0434662728afb95d72455bf30ece5817
> >
> > Quoting the commit message from that patch:
> >
> > ====
> > With clang from git master, code can be generated where a function contains
> > two indirect jump instructions that use the same switch table. To deal with
> > this case and similar ones properly, convert the switch table parsing to
> > use two passes:
> > ====
> >
> > Does that sound like what you're seeing?
>
> Yes, that is exactly right, and your patch seems to address the problem
> for the cases I tried so far (will know more after a night of randconfig
> testing).

I no longer see any of the "can't find switch jump table" in last
nights randconfig
builds. I do see one other rare warning, see attached object file:

fs/reiserfs/do_balan.o: warning: objtool: replace_key()+0x158: stack
state mismatch: cfa1=7+40 cfa2=7+56
fs/reiserfs/do_balan.o: warning: objtool: balance_leaf()+0x2791: stack
state mismatch: cfa1=7+176 cfa2=7+192
fs/reiserfs/ibalance.o: warning: objtool: balance_internal()+0xe8f:
stack state mismatch: cfa1=7+240 cfa2=7+248
fs/reiserfs/ibalance.o: warning: objtool:
internal_move_pointers_items()+0x36f: stack state mismatch: cfa1=7+152
cfa2=7+144
fs/reiserfs/lbalance.o: warning: objtool:
leaf_cut_from_buffer()+0x58b: stack state mismatch: cfa1=7+128
cfa2=7+112
fs/reiserfs/lbalance.o: warning: objtool:
leaf_copy_boundary_item()+0x7a9: stack state mismatch: cfa1=7+104
cfa2=7+96
fs/reiserfs/lbalance.o: warning: objtool:
leaf_copy_items_entirely()+0x3d2: stack state mismatch: cfa1=7+120
cfa2=7+128

I suspect this comes from the calls to the __reiserfs_panic() noreturn function,
but have not actually looked at the object file.

      Arnd

Download attachment "lbalance.o" of type "application/x-object" (40000 bytes)