[PATCH v2 3/4] Kbuild: make DWARF version a choice

Nick Desaulniers
2020-11-04T00:53:56Z

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: Fangrui Song <maskray@google.com>
Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
Makefile | 14 ++++++++------
lib/Kconfig.debug | 19 +++++++++++++++----
2 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/Makefile b/Makefile
index 75b1a3dcbf30..e23786a4c1c7 100644
--- a/Makefile
+++ b/Makefile
@@ -826,12 +826,14 @@ else
DEBUG_CFLAGS += -g
endif

-ifndef LLVM_IAS
-KBUILD_AFLAGS += -Wa,-gdwarf-2
-endif
-
-ifdef CONFIG_DEBUG_INFO_DWARF4
-DEBUG_CFLAGS += -gdwarf-4
+dwarf-version-$(CONFIG_DEBUG_INFO_DWARF2) := 2
+dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
+DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y)
+ifneq ($(dwarf-version-y)$(LLVM_IAS),21)
+# Binutils 2.35+ required for -gdwarf-4+ support.
+dwarf-aflag := $(call as-option,-Wa$(comma)-gdwarf-$(dwarf-version-y))
+DEBUG_CFLAGS += $(dwarf-aflag)
+KBUILD_AFLAGS += $(dwarf-aflag)
endif

ifdef CONFIG_DEBUG_INFO_REDUCED
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 83a860126897..03c494eefabd 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -256,14 +256,25 @@ 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 v2 debuginfo"
+ help
+ Generate DWARF v2 debug info.
+
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.
- 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"
--
2.29.1.341.ge80a0c044ae-goog