linux-kernel - Re: Linux 4.19 and GCC 9

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Message-ID: <CABWYdi1cPLUGws9bxk3FxVKO1v0i-GrKaov0kAJFuLBf8AS25w@mail.gmail.com>
Date:   Thu, 16 May 2019 14:24:48 -0700
From:   Ivan Babrou <ivan@...udflare.com>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        kernel-team <kernel-team@...udflare.com>
Subject: Re: Linux 4.19 and GCC 9

On Thu, May 16, 2019 at 2:21 PM Miguel Ojeda
<miguel.ojeda.sandonis@...il.com> wrote:
>
> Hi,
>
> On Thu, May 16, 2019 at 10:11 PM Ivan Babrou <ivan@...udflare.com> wrote:
> >
> > Hey Miguel,
> >
> > The first error is during perf build process (make -C tools/perf install):
> >
> > [17:38:21] In file included from /usr/include/string.h:635,
> > [17:38:21]                  from ui/tui/helpline.c:4:
> > [17:38:21] In function 'strncpy',
> > [17:38:21]     inlined from 'tui_helpline__push' at ui/tui/helpline.c:27:2:
> > [17:38:21] /usr/include/x86_64-linux-gnu/bits/string3.h:126:10: error:
> > '__builtin_strncpy' specified bound 512 equals destination size
> > [-Werror=stringop-truncation]
> > [17:38:21]   126 |   return __builtin___strncpy_chk (__dest, __src,
> > __len, __bos (__dest));
> > [17:38:21]       |
> > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > [17:38:21] cc1: all warnings being treated as errors
> > [17:38:21] /cfsetup_build/build/linux-4.19.43/tools/build/Makefile.build:96:
> > recipe for target '/cfsetup_build/build/amd64/perf/ui/tui/helpline.o'
> > failed
> > [17:38:21] mv: cannot stat
> > '/cfsetup_build/build/amd64/perf/ui/tui/.helpline.o.tmp': No such file
> > or directory
> > [17:38:21] make[6]: ***
> > [/cfsetup_build/build/amd64/perf/ui/tui/helpline.o] Error 1
> > [17:38:21] make[5]: *** [tui] Error 2
> > [17:38:21] make[4]: *** [ui] Error 2
> >
> > I see that stringop-truncation is disabled in toplevel Makefile, but
> > not sure if perf is using it.
>
> Ah, alright -- CC'ing the perf maintainers then in case they want to chime in.
>
> > If I disable perf build, the next thing is warnings like these:
> >
> > mm/slub.o: warning: objtool: init_cache_random_seq()+0x36: sibling
> > call from callable instruction with modified stack frame
> > mm/slub.o: warning: objtool: slab_out_of_memory()+0x3b: sibling call
> > from callable instruction with modified stack frame
> > mm/slub.o: warning: objtool: slab_pad_check.part.0()+0x7c: sibling
> > call from callable instruction with modified stack frame
> > mm/slub.o: warning: objtool: check_slab()+0x1c: sibling call from
> > callable instruction with modified stack frame
>
> AFAIK those are non-critical, i.e. stack traces may be wrong (or not),
> but it does not mean the generated kernel itself is wrong. CC'ing the
> objtool maintainers too.

I really like my stack traces definitely correct :)

Thanks for looping in the right people.

> > After patching that I see:
> >
> > In file included from /tmp/build/linux-4.19.43/arch/x86/crypto/aes_glue.c:6:
> > /tmp/build/linux-4.19.43/include/linux/module.h:133:6: warning:
> > 'init_module' specifies less restrictive attribute than its target
> > 'aes_init': 'cold' [-Wmissing-attributes]
> >   133 |  int init_module(void) __attribute__((alias(#initfn)));
> >       |      ^~~~~~~~~~~
> > /tmp/build/linux-4.19.43/arch/x86/crypto/aes_glue.c:64:1: note: in
> > expansion of macro 'module_init'
> >    64 | module_init(aes_init);
> >       | ^~~~~~~~~~~
> > /tmp/build/linux-4.19.43/arch/x86/crypto/aes_glue.c:54:19: note:
> > 'init_module' target declared here
> >    54 | static int __init aes_init(void)
> >       |                   ^~~~~~~~
>
> Ditto here, those can be ignored too (unless something has changed in
> GCC that I am not aware of).
>
> > I'm not really comfortable with all the warnings, so I stopped the
> > build, maybe it indeed compiles through the end.
>
> It does (on my GCC 9.1.1 compiled from source).
>
> I am not sure what is the policy on backporting (someone from the
> stable team can probably answer that; Greg?), but note that this
> kernel (and 4.20 and 5.0) was released before GCC 9 did -- and some
> (all?) of this was cleaned up before GCC 9 itself released, so we were
> ahead of it :-)
>
> Cheers,
> Miguel