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kbuild: Remove $(cc-option,-gdwarf-4) dependency from DEBUG_INFO_DWARF4
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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 --gdwarf-[345] options. [1]
And, also we have Clang integrated assembler. So, the debug info
for *.S files might be improved in the future.

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>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
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Masahiro Yamada committed Feb 11, 2021
1 parent db4632c commit 83272e6
Showing 1 changed file with 0 additions and 1 deletion.
1 change: 0 additions & 1 deletion lib/Kconfig.debug
Original file line number Diff line number Diff line change
Expand Up @@ -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.
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