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

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Message-ID: <CAG48ez3ipuPHLxbqqc50=Kn4QuoNczkd7VqEoLPVd3WWLk2s+Q@mail.gmail.com>
Date:   Thu, 11 Jul 2019 23:04:35 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Arnd Bergmann <arnd@...db.de>
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 11:00 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Thu, Jul 11, 2019 at 7:26 PM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> >
> > On Thu, Jul 11, 2019 at 02:40:06PM +0200, Arnd Bergmann wrote:
> > > During randconfig testing with clang-9, I came across an object file
> > > that makes objtool segfault, see attachment. Let me know if you need
> > > more information to
> > > debug this.
> > >
> > > I also get a ton of objtool warnings building random configurations, but Nick
> > > mentioned that there is still a bug related to asm-goto in the build I'm using
> > > that may be the root cause. Once I have a fixed clang-9 build, I can have a look
> > > at those as well.
> >
> > Seg fault fix:
>
> Thanks for the fix! testing it over night now, will let you know tomorrow
> if problems remain.
>
> I wonder if this is also related to several warnings I get about switch
> tables like:
>
> drivers/usb/misc/sisusbvga/sisusb.o: warning: objtool:
> sisusb_write_mem_bulk()+0x588: can't find switch jump table
>
> drivers/gpu/drm/amd/amdgpu/../display/dc/dce110/dce110_mem_input_v.o:
> warning: objtool: dce_mem_input_v_program_pte_vm()+0x46e: can't find
> switch jump table
> drivers/gpu/drm/amd/amdgpu/../display/dc/dce110/dce110_opp_csc_v.o:
> warning: objtool: dce110_opp_v_set_csc_default()+0x714: can't find
> switch jump table
> drivers/gpu/drm/nouveau/nvkm/subdev/clk/nv50.o: warning: objtool:
> nv50_clk_read()+0x15c: can't find switch jump table
> drivers/media/dvb-frontends/cxd2880/cxd2880_tnrdmd_dvbt2.o: warning:
> objtool: x_tune_dvbt2_demod_setting()+0x992: can't find switch jump
> table
> drivers/media/tuners/mt2063.o: warning: objtool:
> MT2063_SetReceiverMode()+0x24d: can't find switch jump table
> drivers/mmc/host/tifm_sd.o: warning: objtool: tifm_sd_exec()+0x7e:
> can't find switch jump table
> drivers/mtd/nand/raw/fsl_ifc_nand.o: warning: objtool:
> fsl_ifc_nand_probe()+0x4c7: can't find switch jump table
> drivers/net/can/at91_can.o: warning: objtool: at91_irq()+0x347: can't
> find switch jump table
> drivers/net/phy/phylink.o: warning: objtool:
> phylink_mac_config()+0x2b5: can't find switch jump table
> drivers/regulator/max8973-regulator.o: warning: objtool:
> max8973_probe()+0x736: can't find switch jump table
> drivers/regulator/tps80031-regulator.o: warning: objtool:
> tps80031_regulator_probe()+0x143: can't find switch jump table
> drivers/tty/cyclades.o: warning: objtool: cy_set_line_char()+0x86c:
> can't find switch jump table
> drivers/tty/serial/jsm/jsm_cls.o: warning: objtool: cls_param()+0x10b:
> can't find switch jump table
> drivers/tty/serial/jsm/jsm_neo.o: warning: objtool: neo_param()+0x151:
> can't find switch jump table
> drivers/usb/core/hub.o: warning: objtool: hub_probe()+0x920: can't
> find switch jump table
> drivers/usb/misc/sisusbvga/sisusb.o: warning: objtool:
> sisusb_write_mem_bulk()+0x4db: can't find switch jump table
> kernel/rcu/tree.o: warning: objtool: rcu_note_context_switch()+0x6b8:
> can't find switch jump table
> lib/zstd/decompress.o: warning: objtool:
> ZSTD_decodeLiteralsBlock()+0x5e: can't find switch jump table
>
> If you want to have a look, I can provide object files and/or reduced test
> cases for this. My guess is that it is unrelated to the warnings that Nick
> saw for asm-goto.

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?