From: Arvind Sankar <nivedita@alum.mit.edu>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Arvind Sankar <nivedita@alum.mit.edu>,
Masahiro Yamada <masahiroy@kernel.org>,
Jakub Jelinek <jakub@redhat.com>,
Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-toolchains@vger.kernel.org,
clang-built-linux <clang-built-linux@googlegroups.com>,
Fangrui Song <maskray@google.com>,
Nathan Chancellor <natechancellor@gmail.com>,
Sedat Dilek <sedat.dilek@gmail.com>,
Dmitry Golovin <dima@golovin.in>,
Alistair Delva <adelva@google.com>
Subject: Re: [PATCH v2 4/4] Kbuild: implement support for DWARF v5
Date: Fri, 4 Dec 2020 12:06:08 -0500 [thread overview]
Message-ID: <X8psgMuL4jMjP/Oy@rani.riverdale.lan> (raw)
In-Reply-To: <CAKwvOdmEVM67v8PqPWHP-VyGTkQpkWv8FdOTbxQ-7ebvSummMA@mail.gmail.com>
On Thu, Dec 03, 2020 at 03:28:14PM -0800, Nick Desaulniers wrote:
> On Thu, Dec 3, 2020 at 3:22 PM Nick Desaulniers <ndesaulniers@google.com> wrote:
> >
> > On Tue, Nov 24, 2020 at 9:28 AM Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > >
> > > On Tue, Nov 03, 2020 at 04:53:43PM -0800, Nick Desaulniers wrote:
> > > > DWARF v5 is the latest standard of the DWARF debug info format.
> > > >
> > > > Feature detection of DWARF5 is onerous, especially given that we've
> > > > removed $(AS), so we must query $(CC) for DWARF5 assembler directive
> > > > support. GNU `as` only recently gained support for specifying
> > > > -gdwarf-5.
> > >
> > > With gcc, using -gdwarf-5 even without -Wa,--gdwarf-5 results in
> > > considerably smaller debug info. gcc does not seem to generate the .file 0
> > > directive that causes older GNU as to barf.
> > >
> > > Should the assembler support check be restricted to CC_IS_CLANG?
> >
> > No, because if LLVM_IAS=1 then the assembler support need not be checked.
>
> Also, if your version of GCC supports DWARF Version 5, but your
> version of GAS does not, then I'm more inclined to not allow
> CONFIG_DEBUG_INFO_DWARF5 to be selectable, rather than mix and match
> or partially support this for one but not the other. Either all tools
> used support DWARF 5, or you don't get to use DWARF 5.
>
Why? Does this actually cause any problems?
It seems like the options for gcc can actually be very straightforward:
you just need a cc-option check, and then add -gdwarf-N to both CFLAGS
and AFLAGS and you're done. Adding the -Wa flag is superfluous and
carries the risk of interfering with what the compiler driver does. Just
let the gcc driver handle the details.
Clang/IAS is almost as straightforward, with the only additional edge
case being that for assembler files, DWARF 2 doesn't work, so the CFLAGS
is the same -gdwarf-N, but AFLAGS gets -gdwarf-N only if N > 2.
The messy case is only Clang/IAS=0, which needs to check the support
from the external assembler, and needs CFLAGS of -gdwarf-N and AFLAGS of
-Wa,--gdwarf-N, because Clang doesn't pass that option on to an external
assembler. This is why I was asking if the assembler support check can
be restricted to CC_IS_CLANG: nothing but Clang/IAS=0 actually requires
that check.
next prev parent reply other threads:[~2020-12-04 17:07 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-22 1:21 [PATCH] Kbuild: implement support for DWARF5 Nick Desaulniers
2020-10-22 1:44 ` Fangrui Song
2020-11-03 22:27 ` Nick Desaulniers
2020-10-28 18:18 ` Nick Desaulniers
2020-11-02 2:20 ` Masahiro Yamada
2020-11-02 8:18 ` Jakub Jelinek
2020-11-03 22:21 ` Nick Desaulniers
2020-11-04 12:19 ` Jakub Jelinek
2020-11-03 22:13 ` Nick Desaulniers
2020-11-04 0:53 ` [PATCH v2 0/4] Kbuild: DWARF v5 support Nick Desaulniers
2020-11-04 0:53 ` [PATCH v2 1/4] x86_64: Change .weak to SYM_FUNC_START_WEAK for arch/x86/lib/mem*_64.S Nick Desaulniers
2020-11-04 0:53 ` [PATCH v2 2/4] Kbuild: do not emit debug info for assembly with LLVM_IAS=1 Nick Desaulniers
2020-11-05 6:58 ` Nathan Chancellor
2020-11-05 7:26 ` Fangrui Song
2020-11-09 18:28 ` Nick Desaulniers
2020-11-09 18:35 ` [PATCH v3] " Nick Desaulniers
2020-11-16 23:41 ` Nick Desaulniers
[not found] ` <CA+SOCLJTg6U+Ddop_5O-baVR42va3vGAvMQ62o9H6rd+10aKrw@mail.gmail.com>
2020-11-23 18:42 ` Nick Desaulniers
2020-11-24 18:44 ` Masahiro Yamada
2020-11-04 0:53 ` [PATCH v2 3/4] Kbuild: make DWARF version a choice Nick Desaulniers
2020-11-05 5:58 ` kernel test robot
2020-11-23 23:22 ` Arvind Sankar
2020-11-24 0:33 ` Segher Boessenkool
2020-11-24 16:56 ` Arvind Sankar
2020-11-24 17:46 ` Segher Boessenkool
2020-11-30 18:04 ` Masahiro Yamada
2020-11-30 20:27 ` Fāng-ruì Sòng
2020-12-01 3:38 ` Masahiro Yamada
2020-12-01 9:32 ` Segher Boessenkool
2020-12-02 1:08 ` Fāng-ruì Sòng
2020-11-30 20:45 ` Nick Desaulniers
2020-12-01 4:17 ` Masahiro Yamada
2020-11-04 0:53 ` [PATCH v2 4/4] Kbuild: implement support for DWARF v5 Nick Desaulniers
2020-11-24 17:28 ` Arvind Sankar
2020-12-03 23:22 ` Nick Desaulniers
2020-12-03 23:28 ` Nick Desaulniers
2020-12-04 17:06 ` Arvind Sankar [this message]
2020-12-10 23:18 ` Nick Desaulniers
2020-12-11 0:29 ` Arvind Sankar
2020-12-01 1:56 ` Masahiro Yamada
2020-11-04 0:00 ` [PATCH] Kbuild: implement support for DWARF5 Arvind Sankar
2020-11-04 0:05 ` Nick Desaulniers
2020-11-04 0:17 ` Arvind Sankar
2020-12-03 22:56 ` Nick Desaulniers
2020-12-04 0:17 ` Nick Desaulniers
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