linux-kernel - Re: [PATCH v2 00/20] objtool: vmlinux.o and CLANG LTO support

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Message-ID: <20210123024634.qu62tyq3nkqusken@treble>
Date:   Fri, 22 Jan 2021 20:46:34 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Sedat Dilek <sedat.dilek@...il.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        Miroslav Benes <mbenes@...e.cz>,
        Fangrui Song <maskray@...gle.com>,
        Peter Collingbourne <pcc@...gle.com>
Subject: Re: [PATCH v2 00/20] objtool: vmlinux.o and CLANG LTO support

On Sat, Jan 23, 2021 at 03:31:20AM +0100, Sedat Dilek wrote:
> On Sat, Jan 23, 2021 at 3:26 AM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> >
> > On Fri, Jan 22, 2021 at 05:32:43PM -0800, Nick Desaulniers wrote:
> > > > In this specific case, find_func_by_offset returns NULL for
> > > > .text..L.cfi.jumptable.43 at addend 0x8, because Clang doesn't emit
> > > > jump table symbols for static functions:
> > > >
> > > > 0000000000000000 <__typeid__ZTSFjmiE_global_addr>:
> > > >    0:   e9 00 00 00 00          jmpq   5 <__typeid__ZTSFjmiE_global_addr+0x5>
> > > >                         1: R_X86_64_PLT32       io_serial_in-0x4
> > > >    5:   cc                      int3
> > > >    6:   cc                      int3
> > > >    7:   cc                      int3
> > > >    8:   e9 00 00 00 00          jmpq   d <__typeid__ZTSFjmiE_global_addr+0xd>
> > > >                         9: R_X86_64_PLT32       mem32_serial_in-0x4
> > > >    d:   cc                      int3
> > > >    e:   cc                      int3
> > > >    f:   cc                      int3
> > > >
> > > > Nick, do you remember if there were plans to change this?
> > >
> > > Do you have a link to any previous discussion to help jog my mind; I
> > > don't really remember this one.
> > >
> > > Is it that `__typeid__ZTSFjmiE_global_addr` is the synthesized jump
> > > table, and yet there is no `__typeid__ZTSFjmiE_global_addr` entry in
> > > the symbol table?
> >
> > I think he means there's not a 'mem32_serial_in.cfi_jt' symbol at
> > '__typeid__ZTSFjmiE_global_addr+8'.  Probably more aggressive symbol
> > pruning from the assembler.
> >
> > It's fine though.  I just need to rewrite the CFI support a bit.
> >
> > But that can come later.  For now I'll just drop the two CFI-related
> > patches from this set so I can merge the others next week.
> >
> 
> Two CFI-related patches?
> 
> What's the other than "objtool: Add CONFIG_CFI_CLANG support"?

I was referring to patches 10 and 11:

  objtool: Move unsuffixed symbol conversion to a helper function
  objtool: Add CONFIG_CFI_CLANG support

You can just drop those patches from your testing (and don't test with
CFI).

> Do you plan (or offer) a v3 of objtool-vmlinux?

Not unless there are any more comments.

-- 
Josh