linux-kernel - Re: [PATCH v5 1/3] Remove $(cc-option,-gdwarf-4) dependency from CONFIG_DEBUG_INFO

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Date:   Wed, 20 Jan 2021 14:57:49 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Sedat Dilek <sedat.dilek@...il.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Jakub Jelinek <jakub@...hat.com>,
        Fangrui Song <maskray@...gle.com>,
        Caroline Tice <cmtice@...gle.com>,
        Nick Clifton <nickc@...hat.com>, Yonghong Song <yhs@...com>,
        Jiri Olsa <jolsa@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH v5 1/3] Remove $(cc-option,-gdwarf-4) dependency from CONFIG_DEBUG_INFO_DWARF4

On Sat, Jan 16, 2021 at 8:54 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> On Sat, Jan 16, 2021 at 6:51 AM Nick Desaulniers
> <ndesaulniers@...gle.com> wrote:
> >
> > On Fri, Jan 15, 2021 at 1:48 PM Sedat Dilek <sedat.dilek@...il.com> wrote:
> > >
> > > On Fri, Jan 15, 2021 at 10:06 PM Nick Desaulniers
> > > <ndesaulniers@...gle.com> wrote:
> > > >
> > > > From: Masahiro Yamada <masahiroy@...nel.org>
> > > >
> > > > The -gdwarf-4 flag is supported by GCC 4.5+, and also by Clang.
> > > >
> > > > You can see it at https://godbolt.org/z/6ed1oW
> > > >
> > > >   For gcc 4.5.3 pane,    line 37:    .value 0x4
> > > >   For clang 10.0.1 pane, line 117:   .short 4
> > > >
> > > > Given Documentation/process/changes.rst stating GCC 4.9 is the minimal
> > > > version, this cc-option is unneeded.
> > > >
> > > > Note
> > > > ----
> > > >
> > > > CONFIG_DEBUG_INFO_DWARF4 controls the DWARF version only for C files.
> > > >
> > > > As you can see in the top Makefile, -gdwarf-4 is only passed to CFLAGS.
> > > >
> > > >   ifdef CONFIG_DEBUG_INFO_DWARF4
> > > >   DEBUG_CFLAGS    += -gdwarf-4
> > > >   endif
> > > >
> > > > This flag is used when compiling *.c files.
> > > >
> > > > On the other hand, the assembler is always given -gdwarf-2.
> > > >
> > > >   KBUILD_AFLAGS   += -Wa,-gdwarf-2
> > > >
> > > > Hence, the debug info that comes from *.S files is always DWARF v2.
> > > > This is simply because GAS supported only -gdwarf-2 for a long time.
> > > >
> > > > Recently, GAS gained the support for --dwarf-[3|4|5] options. [1]
> > > > And, also we have Clang integrated assembler. So, the debug info
> > > > for *.S files might be improved if we want.
> > > >
> > > > In my understanding, the current code is intentional, not a bug.
> > > >
> > > > [1] https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=31bf18645d98b4d3d7357353be840e320649a67d
> > > >
> > > > Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> > > > Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
> > > > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> > >
> > > Subject misses a "kbuild:" label like in all other patches.
> > > You have:
> > > "Remove $(cc-option,-gdwarf-4) dependency from CONFIG_DEBUG_INFO_DWARF4"
> >
> > Ack, I wonder how that happened? Ah well, will fix in v6; thanks for
> > the feedback.
>
>
>
> I will apply this in my tree,
> adding "kbuild:" and fixing the typo pointed out by Fangrui.
>
> You do not need to resend this one.
>



Applied to linux-kbuild.


>
>
>
>
>
>
> > >
> > > - Sedat -
> > >
> > > > ---
> > > >  lib/Kconfig.debug | 1 -
> > > >  1 file changed, 1 deletion(-)
> > > >
> > > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > > > index 78361f0abe3a..dd7d8d35b2a5 100644
> > > > --- a/lib/Kconfig.debug
> > > > +++ b/lib/Kconfig.debug
> > > > @@ -258,7 +258,6 @@ config DEBUG_INFO_SPLIT
> > > >
> > > >  config DEBUG_INFO_DWARF4
> > > >         bool "Generate dwarf4 debuginfo"
> > > > -       depends on $(cc-option,-gdwarf-4)
> > > >         help
> > > >           Generate dwarf4 debug info. This requires recent versions
> > > >           of gcc and gdb. It makes the debug information larger.
> > > > --
> > > > 2.30.0.284.gd98b1dd5eaa7-goog
> > > >
> >
> >
> >
> > --
> > Thanks,
> > ~Nick Desaulniers
>
>
>
> --
> Best Regards
> Masahiro Yamada



-- 
Best Regards
Masahiro Yamada