Re: [PATCH v4] Makefile.debug: re-enable debug info for .S files

From: Masahiro Yamada <masahiroy@kernel.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Michal Marek <michal.lkml@markovi.net>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	clang-built-linux <llvm@lists.linux.dev>,
	Bill Wendling <morbo@google.com>,
	Greg Thelen <gthelen@google.com>,
	Alexey Alexandrov <aalexand@google.com>,
	Nathan Chancellor <nathan@kernel.org>
Subject: Re: [PATCH v4] Makefile.debug: re-enable debug info for .S files
Date: Sat, 24 Sep 2022 15:43:22 +0900	[thread overview]
Message-ID: <CAK7LNARfiq4fONgRKpO-FOAUNitVwmr=if+04pJfa62aamjSOw@mail.gmail.com> (raw)
In-Reply-To: <CAKwvOdk-oj24MQs-W0Xs6p33f+Ei7Wu3wwCX+d34T=xoOPxOiw@mail.gmail.com>

On Sat, Sep 24, 2022 at 11:20 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Fri, Sep 23, 2022 at 7:12 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > This patch still misses the debug info for *.S files
> > for the combination of LLVM_IAS=0 and
> > CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
> > because, as the comment says, Clang does not pass -g down to GAS.
> >
> >
> > With "[v4] Makefile.debug: set -g unconditional on CONFIG_DEBUG_INFO_SPLIT"
> > and this one applied,
> >
> >
> >
> > $ grep CONFIG_DEBUG_INFO_DWARF .config
> > CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
> > # CONFIG_DEBUG_INFO_DWARF4 is not set
> > # CONFIG_DEBUG_INFO_DWARF5 is not set
> > $ make LLVM=1 LLVM_IAS=0 arch/x86/kernel/irqflags.o
> >   SYNC    include/config/auto.conf.cmd
> >   SYSHDR  arch/x86/include/generated/asm/unistd_32_ia32.h
> >   SYSHDR  arch/x86/include/generated/asm/unistd_64_x32.h
> >   SYSTBL  arch/x86/include/generated/asm/syscalls_64.h
> >   HOSTCC  arch/x86/tools/relocs_32.o
> >   [snip]
> >   AS      arch/x86/kernel/irqflags.o
> > $ objdump  -h arch/x86/kernel/irqflags.o | grep debug
> > $
> >
> >
> >
> >
> >
> >
> >
> >
> > I think the following fix-up is needed on top.
> >
> >
> >
> >
> > diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug
> > index d6aecd78b942..8cf1cb22dd93 100644
> > --- a/scripts/Makefile.debug
> > +++ b/scripts/Makefile.debug
> > @@ -1,4 +1,5 @@
> > -DEBUG_CFLAGS   := -g
> > +DEBUG_CFLAGS   :=
> > +debug-flags-y  := -g
> >
> >  ifdef CONFIG_DEBUG_INFO_SPLIT
> >  DEBUG_CFLAGS   += -gsplit-dwarf
> >
> >
> >
> >
> > Then, I can see the debug sections.
> >
> >
> >
> > $ make LLVM=1 LLVM_IAS=0 arch/x86/kernel/irqflags.o
> >   CALL    scripts/checksyscalls.sh
> >   DESCEND objtool
> >   AS      arch/x86/kernel/irqflags.o
> > $ objdump -h arch/x86/kernel/irqflags.o | grep debug
> >   6 .debug_line   00000050  0000000000000000  0000000000000000  0000008f  2**0
> >   7 .debug_info   0000002e  0000000000000000  0000000000000000  000000f8  2**0
> >   8 .debug_abbrev 00000014  0000000000000000  0000000000000000  000001d0  2**0
> >   9 .debug_aranges 00000030  0000000000000000  0000000000000000  000001f0  2**4
> >  10 .debug_str    0000004d  0000000000000000  0000000000000000  00000250  2**0
> >
> >
> >
> >
> >
> > If you agree, I can locally fix it up as such.
>
> Ah, sorry I missed testing that combination. Thanks for your
> thoroughness. Yes please apply that diff on top.
> --
> Thanks,
> ~Nick Desaulniers

Applied to linux-kbuild with the fixup.

-- 
Best Regards
Masahiro Yamada