linux-kernel - Re: objtool warning "uses BP as a scratch register" with clang-9

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Date:   Wed, 28 Aug 2019 12:57:13 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Ilie Halip <ilie.halip@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: objtool warning "uses BP as a scratch register" with clang-9

On Wed, Aug 28, 2019 at 05:29:39PM +0200, Arnd Bergmann wrote:
> On Wed, Aug 28, 2019 at 4:51 PM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> > On Wed, Aug 28, 2019 at 11:00:04AM +0200, Arnd Bergmann wrote:
> > > On Tue, Aug 27, 2019 at 11:22 PM 'Nick Desaulniers' via Clang Built
> > > Linux <clang-built-linux@...glegroups.com> wrote:
> > > > On Tue, Aug 27, 2019 at 12:47 PM Arnd Bergmann <arnd@...db.de> wrote:
> > >
> > > Only a few unique objtool warnings remain now, here are the ones I
> > > currently see,
> > > along with .config files. Let me know which ones I should investigate further,
> > > I assume a lot of these are known issues:
> >
> > None of those look necessarily familiar.  What are the remaining "known"
> > clang issues which were found by objtool?
> 
> Maybe Nick can identify some.
> 
> > If you share .o files I can look at them.
> 
> Attaching the ones I could easily recreate here.

adm1275.o: warning: objtool: adm1275_probe()+0x756: unreachable instruction
- known issue: clang switch table has invalid entries
- also an objtool bug: need to report it as "falls through to next function"

atom.o: warning: objtool: atom_op_move() falls through to next function atom_op_and()
evergreen_cs.o: warning: objtool: evergreen_cs_parse() falls through to next function evergreen_dma_cs_parse()
- known issue: clang switch table has invalid entries

common.o: warning: objtool: kasan_report()+0x52: call to __stack_chk_fail() with UACCESS enabled
trace_branch.o: warning: objtool: ftrace_likely_update()+0x6c: call to __stack_chk_fail() with UACCESS enabled
- objtool bug: need to add __stack_chk_fail to uaccess whitelist

cxd2880_tnrdmd_dvbt2.o: warning: objtool: x_tune_dvbt2_demod_setting()+0x7f6: can't find switch jump table
- objtool bug: tricky switch table issue

exit.o: warning: objtool: abort()+0x3: unreachable instruction
hugetlb.o: warning: objtool: hugetlb_vm_op_fault()+0x3: unreachable instruction
idle.o: warning: objtool: switched_to_idle()+0x3: unreachable instruction
madvise.o: warning: objtool: hugepage_madvise()+0x3: unreachable instruction
privcmd.o: warning: objtool: privcmd_ioctl_mmap_batch()+0x5dd: unreachable instruction
process.o: warning: objtool: play_dead()+0x3: unreachable instruction
rmap.o: warning: objtool: anon_vma_clone()+0x1c2: unreachable instruction
s5c73m3-core.o: warning: objtool: s5c73m3_probe()+0x262: unreachable instruction
videobuf2-core.o: warning: objtool: vb2_core_dqbuf()+0xae6: unreachable instruction
xfrm_output.o: warning: objtool: xfrm_outer_mode_output()+0x109: unreachable instruction
- clang issue: trying to finish frame pointer setup after BUG() in unreachable code path

pinctrl-ingenic.o: warning: objtool: ingenic_pinconf_set()+0x10d: sibling call from callable instruction with modified stack frame
- bad clang bug: sibling call without first popping registers

-- 
Josh