Modifies CONFIG_DEBUG_INFO_DWARF4 to be a member of a choice. Adds an
explicit CONFIG_DEBUG_INFO_DWARF2, which is the default. Does so in a
way that's forward compatible with existing configs, and makes adding
future versions more straightforward.

Suggested-by: Arvind Sankar <nived...@alum.mit.edu>
Suggested-by: Fangrui Song <mask...@google.com>
Suggested-by: Nathan Chancellor <nat...@kernel.org>
Suggested-by: Masahiro Yamada <masahi...@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulni...@google.com>
---
 Makefile          |  6 +++---
 lib/Kconfig.debug | 21 ++++++++++++++++-----
 2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/Makefile b/Makefile
index 95ab9856f357..20141cd9319e 100644
--- a/Makefile
+++ b/Makefile
@@ -830,9 +830,9 @@ ifneq ($(LLVM_IAS),1)
 KBUILD_AFLAGS  += -Wa,-gdwarf-2
 endif
 
-ifdef CONFIG_DEBUG_INFO_DWARF4
-DEBUG_CFLAGS   += -gdwarf-4
-endif
+dwarf-version-$(CONFIG_DEBUG_INFO_DWARF2) := 2
+dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
+DEBUG_CFLAGS   += -gdwarf-$(dwarf-version-y)
 
 ifdef CONFIG_DEBUG_INFO_REDUCED
 DEBUG_CFLAGS   += $(call cc-option, -femit-struct-debug-baseonly) \
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index e906ea906cb7..1850728b23e6 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -256,13 +256,24 @@ config DEBUG_INFO_SPLIT
          to know about the .dwo files and include them.
          Incompatible with older versions of ccache.
 
+choice
+       prompt "DWARF version"
+       help
+         Which version of DWARF debug info to emit.
+
+config DEBUG_INFO_DWARF2
+       bool "Generate DWARF Version 2 debuginfo"
+       help
+         Generate DWARF v2 debug info.
+
 config DEBUG_INFO_DWARF4
-       bool "Generate dwarf4 debuginfo"
+       bool "Generate DWARF Version 4 debuginfo"
        help
-         Generate dwarf4 debug info. This requires recent versions
-         of gcc and gdb. It makes the debug information larger.
-         But it significantly improves the success of resolving
-         variables in gdb on optimized code.
+         Generate DWARF v4 debug info. This requires gcc 4.5+ and gdb 7.0+.
+         It makes the debug information larger, but it significantly
+         improves the success of resolving variables in gdb on optimized code.
+
+endchoice # "DWARF version"
 
 config DEBUG_INFO_BTF
        bool "Generate BTF typeinfo"
-- 
2.30.0.365.g02bc693789-goog

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