From: Nick Desaulniers <ndesaulniers@google.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
clang-built-linux <clang-built-linux@googlegroups.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Craig Topper <craig.topper@intel.com>,
Simon Pilgrim <llvm-dev@redking.me.uk>
Subject: Re: warning: objtool: fn1 uses BP as a scratch register
Date: Fri, 19 Jul 2019 11:48:14 -0700 [thread overview]
Message-ID: <CAKwvOdkC16irbGpP=cA8eEPvBWj+6mSgVgo+rs1ofDLNufWWzw@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a1hxEAnuqt=ajUf4ETCOY9ckEEVZVrG1c+SV=bn2_Ga-Q@mail.gmail.com>
On Fri, Jul 19, 2019 at 11:44 AM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Fri, Jul 19, 2019 at 8:31 PM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> >
> > On Fri, Jul 19, 2019 at 11:23:16AM -0700, Nick Desaulniers wrote:
> > > On Fri, Jul 19, 2019 at 11:10 AM Arnd Bergmann <arnd@arndb.de> wrote:
> > > >
> > > > A lot of objtool fixes showed up in linux-next, so I looked at some
> > > > remaining ones.
> > > > This one comes a lot up in some configurations
> > > >
> > > > https://godbolt.org/z/ZZLVD-
> > > >
> > > > struct ov7670_win_size {
> > > > int width;
> > > > int height;
> > > > };
> > > > struct ov7670_devtype {
> > > > struct ov7670_win_size *win_sizes;
> > > > unsigned n_win_sizes;
> > > > };
> > > > struct ov7670_info {
> > > > int min_width;
> > > > int min_height;
> > > > struct ov7670_devtype devtype;
> > > > } a;
> > > > int b;
> > > > int fn1() {
> > > > struct ov7670_info c = a;
> > > > int i = 0;
> > > > for (; i < c.devtype.n_win_sizes; i++) {
> > > > struct ov7670_win_size d = c.devtype.win_sizes[i];
> > > > if (c.min_width && d.width < d.height < c.min_height)
> > > > if (b)
> > > > return 0;
> > > > }
> > > > return 2;
> > > > }
> > > >
> > > > $ clang-8 -O2 -fno-omit-frame-pointer -fno-strict-overflow -c ov7670.i
> > > > $ objtool check --no-unreachable --uaccess ov7670.o
> > > > ov7670.o: warning: objtool: fn1 uses BP as a scratch register
> > >
> > > Thanks for the report and reduced test case. From the godbolt link, I
> > > don't see %rbp, %ebp, %bp, or %bpl being referenced (other that %rbp
> > > in the typical epilogue). Am I missing something? Is objtool maybe
> > > not reporting the precise function at fault?
> >
> > I haven't looked, but it could very well be an objtool bug (surprise).
>
> Actually the reproducer may be wrong. I reduced the test case using
> 9.0.0-svn363902-1~exp1+0~20190620001509.2315~1.gbp76e756,
> and this contains a link
>
> testl %ebp, %ebp
>
> I get the same thing with clang-8, but godbolt.org shows it only
> with clang-8 (see https://godbolt.org/z/g1lZO0) , not with trunk.
>
> Arnd
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2019-07-19 18:48 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-19 18:09 warning: objtool: fn1 uses BP as a scratch register Arnd Bergmann
2019-07-19 18:23 ` Nick Desaulniers
2019-07-19 18:31 ` Josh Poimboeuf
2019-07-19 18:44 ` Arnd Bergmann
2019-07-19 18:48 ` Nick Desaulniers [this message]
2019-07-19 18:50 ` Nick Desaulniers
2019-07-19 19:43 ` Arnd Bergmann
2019-07-22 19:46 ` Topper, Craig
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