linux-kernel - Re: [PATCH v6 2/2] Kbuild: implement support for DWARF v5

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Message-ID: <CA+icZUUo6URpxHh6_Tppv9_Z1dyhGDB2OqSCY3yRw72aA0EbMQ@mail.gmail.com>
Date:   Fri, 29 Jan 2021 22:20:10 +0100
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        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>,
        Arvind Sankar <nivedita@...m.mit.edu>
Subject: Re: [PATCH v6 2/2] Kbuild: implement support for DWARF v5

On Fri, Jan 29, 2021 at 10:13 PM Sedat Dilek <sedat.dilek@...il.com> wrote:
>
> On Fri, Jan 29, 2021 at 10:09 PM Nick Desaulniers
> <ndesaulniers@...gle.com> wrote:
> >
> > On Fri, Jan 29, 2021 at 12:55 PM Sedat Dilek <sedat.dilek@...il.com> wrote:
> > >
> > > On Fri, Jan 29, 2021 at 9:48 PM Nick Desaulniers
> > > <ndesaulniers@...gle.com> wrote:
> > > >
> > > > On Fri, Jan 29, 2021 at 12:41 PM Sedat Dilek <sedat.dilek@...il.com> wrote:
> > > > >
> > > > > On Fri, Jan 29, 2021 at 8:43 PM Nick Desaulniers
> > > > > <ndesaulniers@...gle.com> wrote:
> > > > > >
> > > > > > diff --git a/Makefile b/Makefile
> > > > > > index 20141cd9319e..bed8b3b180b8 100644
> > > > > > --- a/Makefile
> > > > > > +++ b/Makefile
> > > > > > @@ -832,8 +832,20 @@ endif
> > > > > >
> > > > > >  dwarf-version-$(CONFIG_DEBUG_INFO_DWARF2) := 2
> > > > > >  dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
> > > > > > +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF5) := 5
> > > > > >  DEBUG_CFLAGS   += -gdwarf-$(dwarf-version-y)
> > > > > >
> > > > > > +# If using clang without the integrated assembler, we need to explicitly tell
> > > > > > +# GAS that we will be feeding it DWARF v5 assembler directives. Kconfig should
> > > > > > +# detect whether the version of GAS supports DWARF v5.
> > > > > > +ifdef CONFIG_CC_IS_CLANG
> > > > > > +ifneq ($(LLVM_IAS),1)
> > > > > > +ifeq ($(dwarf-version-y),5)
> > > > > > +DEBUG_CFLAGS   += -Wa,-gdwarf-5
> > > > >
> > > > > I noticed double "-g -gdwarf-5 -g -gdwarf-5" (a different issue) and
> > > > > that's why I looked again into the top-level Makefile.
> > > >
> > > > That's...unexpected.  I don't see where that could be coming from.
> > > > Can you tell me please what is the precise command line invocation of
> > > > make and which source file you observed this on so that I can
> > > > reproduce?
> > > >
> > >
> > > That's everywhere...
> > >
> > > $ zstdgrep --color '\-g -gdwarf-5 -g -gdwarf-5'
> > > build-log_5.11.0-rc5-8-amd64-clang12-lto.txt.zst
> > > | wc -l
> > > 29529
> >
> > I'm not able to reproduce.
> >
> > $ make LLVM=1 -j72 V=1 2>&1 | grep dwarf
> > ...
> > clang ... -g -gdwarf-5 -Wa,-gdwarf-5 ...
> > ...
> >
> > $ make LLVM=1 LLVM_IAS=1 -j72 V=1 2>&1 | grep dwarf
> > ...
> > clang ... -g -gdwarf-5 ...
> > ...
> >
>
> Hmm...
>
> I do not see in my current build "-Wa,-gdwarf-5" is passed with v6.
>
> $ grep '\-Wa,-gdwarf-5' build-log_5.11.0-rc5-10-amd64-clang12-lto-pgo.txt
> [ empty ]
>

That's the diff v5 -> v6...

[ Makefile ]

@@ -826,16 +829,23 @@ else
 DEBUG_CFLAGS += -g
 endif

+ifneq ($(LLVM_IAS),1)
+KBUILD_AFLAGS += -Wa,-gdwarf-2
+endif
+
 dwarf-version-$(CONFIG_DEBUG_INFO_DWARF2) := 2
 dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
 dwarf-version-$(CONFIG_DEBUG_INFO_DWARF5) := 5
 DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y)
-# Binutils 2.35+ required for -gdwarf-4+ support.
-dwarf-aflag := $(call as-option,-Wa$(comma)-gdwarf-$(dwarf-version-y))
-KBUILD_AFLAGS += $(dwarf-aflag)
+
+# If using clang without the integrated assembler, we need to explicitly tell
+# GAS that we will be feeding it DWARF v5 assembler directives. Kconfig should
+# detect whether the version of GAS supports DWARF v5.
 ifdef CONFIG_CC_IS_CLANG
 ifneq ($(LLVM_IAS),1)
-DEBUG_CFLAGS += $(dwarf-aflag)
+ifeq ($(dwarf-version-y),5)
+DEBUG_CFLAGS += -Wa,-gdwarf-5
+endif
 endif
 endif

There is no more a dwarf-aflag / KBUILD_AFLAGS += $(dwarf-aflag) used.

- Sedat -

>
> - Sedat
>
>
>
>
> > Can you tell me please what is the precise command line invocation of
> > make and which source file you observed this on so that I can
> > reproduce?
> > --
> > Thanks,
> > ~Nick Desaulniers