linux-kernel - Re: [PATCH v6 1/2] Kbuild: make DWARF version a choice

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Date:   Fri, 29 Jan 2021 12:19:46 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Jakub Jelinek <jakub@...hat.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sedat Dilek <sedat.dilek@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        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>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH v6 1/2] Kbuild: make DWARF version a choice

On Fri, Jan 29, 2021 at 12:17 PM Jakub Jelinek <jakub@...hat.com> wrote:
>
> On Fri, Jan 29, 2021 at 11:43:17AM -0800, Nick Desaulniers wrote:
> > Modifies CONFIG_DEBUG_INFO_DWARF4 to be a member of a choice. Adds an
> > explicit CONFIG_DEBUG_INFO_DWARF2, which is the default. Does so in a
> > way that's forward compatible with existing configs, and makes adding
> > future versions more straightforward.
> >
> > Suggested-by: Arvind Sankar <nivedita@...m.mit.edu>
> > Suggested-by: Fangrui Song <maskray@...gle.com>
> > Suggested-by: Nathan Chancellor <nathan@...nel.org>
> > Suggested-by: Masahiro Yamada <masahiroy@...nel.org>
> > Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> > ---
> >  Makefile          |  6 +++---
> >  lib/Kconfig.debug | 21 ++++++++++++++++-----
> >  2 files changed, 19 insertions(+), 8 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index 95ab9856f357..20141cd9319e 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -830,9 +830,9 @@ ifneq ($(LLVM_IAS),1)
> >  KBUILD_AFLAGS        += -Wa,-gdwarf-2
> >  endif
> >
> > -ifdef CONFIG_DEBUG_INFO_DWARF4
> > -DEBUG_CFLAGS += -gdwarf-4
> > -endif
> > +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF2) := 2
> > +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
> > +DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y)
>
> Why do you make DWARF2 the default?  That seems a big step back from what
> the Makefile used to do before, where it defaulted to whatever DWARF version
> the compiler defaulted to?
> E.g. GCC 4.8 up to 10 defaults to -gdwarf-4 and GCC 11 will default to
> -gdwarf-5.
> DWARF2 is more than 27 years old standard, DWARF3 15 years old,
> DWARF4 over 10 years old and DWARF5 almost 4 years old...
> It is true that some tools aren't DWARF5 ready at this point, but with GCC
> defaulting to that it will change quickly, but at least DWARF4 support has
> been around for years.

I agree with you; I also do not want to change the existing defaults
in this series. That is a separate issue to address.

-- 
Thanks,
~Nick Desaulniers