On Sat, Jan 16, 2021 at 8:54 AM Masahiro Yamada [off-list ref] wrote:

On Sat, Jan 16, 2021 at 6:51 AM Nick Desaulniers
[off-list ref] wrote:

quoted

On Fri, Jan 15, 2021 at 1:48 PM Sedat Dilek [off-list ref] wrote:

quoted

On Fri, Jan 15, 2021 at 10:06 PM Nick Desaulniers
[off-list ref] wrote:

quoted

From: Masahiro Yamada <masahiroy@kernel.org>

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

Reviewed-by: Nick Desaulniers <redacted>
Reviewed-by: Nathan Chancellor <redacted>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Subject misses a "kbuild:" label like in all other patches.
You have:
"Remove $(cc-option,-gdwarf-4) dependency from CONFIG_DEBUG_INFO_DWARF4"

Ack, I wonder how that happened? Ah well, will fix in v6; thanks for
the feedback.

I will apply this in my tree,
adding "kbuild:" and fixing the typo pointed out by Fangrui.

You do not need to resend this one.

Applied to linux-kbuild.

quoted

quoted

- Sedat -

quoted

---
 lib/Kconfig.debug | 1 -
 1 file changed, 1 deletion(-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 78361f0abe3a..dd7d8d35b2a5 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.
--

2.30.0.284.gd98b1dd5eaa7-goog

--
Thanks,
~Nick Desaulniers

--
Best Regards
Masahiro Yamada

-- 
Best Regards
Masahiro Yamada