Re: [PATCH v5 1/3] Remove $(cc-option,-gdwarf-4) dependency from CONFIG_DEBUG_INFO_DWARF4

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On 2021-01-15, Nick Desaulniers wrote:
From: Masahiro Yamada <masahiroy@xxxxxxxxxx>

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]

The gas commit description has a typo. The supported options are -gdwarf-[345] or --gdwarf-[345].
-gdwarf2 and --gdwarf2 are kept for compatibility.

Looks good otherwise.

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 <ndesaulniers@xxxxxxxxxx>
Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
---
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




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