* [PATCH] Remove $(cc-option,-gdwarf-4) dependency from CONFIG_DEBUG_INFO_DWARF4
@ 2020-12-01 3:27 Masahiro Yamada
2020-12-01 3:41 ` Masahiro Yamada
0 siblings, 1 reply; 3+ messages in thread
From: Masahiro Yamada @ 2020-12-01 3:27 UTC (permalink / raw)
To: linux-kbuild
Cc: Fangrui Song, Nick Desaulniers, Masahiro Yamada, Andrew Morton,
Changbin Du, Greg Kroah-Hartman, Krzysztof Kozlowski,
Nathan Chancellor, Peter Enderborg, Randy Dunlap,
clang-built-linux, linux-kernel, peterz
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
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---
lib/Kconfig.debug | 1 -
1 file changed, 1 deletion(-)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index cb8ef4fd0d02..7f80c25497a1 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.
--
2.27.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] Remove $(cc-option,-gdwarf-4) dependency from CONFIG_DEBUG_INFO_DWARF4
2020-12-01 3:27 [PATCH] Remove $(cc-option,-gdwarf-4) dependency from CONFIG_DEBUG_INFO_DWARF4 Masahiro Yamada
@ 2020-12-01 3:41 ` Masahiro Yamada
2020-12-02 23:12 ` Nick Desaulniers
0 siblings, 1 reply; 3+ messages in thread
From: Masahiro Yamada @ 2020-12-01 3:41 UTC (permalink / raw)
To: Linux Kbuild mailing list
Cc: Fangrui Song, Nick Desaulniers, Andrew Morton, Changbin Du,
Greg Kroah-Hartman, Krzysztof Kozlowski, Nathan Chancellor,
Peter Enderborg, Randy Dunlap, clang-built-linux,
Linux Kernel Mailing List, peterz
On Tue, Dec 1, 2020 at 12:29 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> 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
>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
>
> lib/Kconfig.debug | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index cb8ef4fd0d02..7f80c25497a1 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.
> --
> 2.27.
Maybe, this can be squashed into Nick's patch.
--
Best Regards
Masahiro Yamada
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] Remove $(cc-option,-gdwarf-4) dependency from CONFIG_DEBUG_INFO_DWARF4
2020-12-01 3:41 ` Masahiro Yamada
@ 2020-12-02 23:12 ` Nick Desaulniers
0 siblings, 0 replies; 3+ messages in thread
From: Nick Desaulniers @ 2020-12-02 23:12 UTC (permalink / raw)
To: Masahiro Yamada
Cc: Linux Kbuild mailing list, Fangrui Song, Andrew Morton,
Changbin Du, Greg Kroah-Hartman, Krzysztof Kozlowski,
Nathan Chancellor, Peter Enderborg, Randy Dunlap,
clang-built-linux, Linux Kernel Mailing List, peterz
On Mon, Nov 30, 2020 at 7:42 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Tue, Dec 1, 2020 at 12:29 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > The -gdwarf-4 flag is supported by GCC 4.5+, and also by Clang.
> >
> > You can see it at https://godbolt.org/z/6ed1oW
(this link misses -gdwarf-4 for clang, but I think that's ok)
> >
> > 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
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> > ---
> >
> > lib/Kconfig.debug | 1 -
> > 1 file changed, 1 deletion(-)
> >
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index cb8ef4fd0d02..7f80c25497a1 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.
> > --
> > 2.27.
>
>
> Maybe, this can be squashed into Nick's patch.
I have no preference.
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
(I'll reroll this into my DWARFv5 series either way, but when/how you
merge this doesn't matter to me)
--
Thanks,
~Nick Desaulniers
^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-12-01 3:27 [PATCH] Remove $(cc-option,-gdwarf-4) dependency from CONFIG_DEBUG_INFO_DWARF4 Masahiro Yamada
2020-12-01 3:41 ` Masahiro Yamada
2020-12-02 23:12 ` Nick Desaulniers
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