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

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Message-Id: <20201104005343.4192504-4-ndesaulniers@google.com>
Date:   Tue,  3 Nov 2020 16:53:42 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Jakub Jelinek <jakub@...hat.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-toolchains@...r.kernel.org,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Fangrui Song <maskray@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Dmitry Golovin <dima@...ovin.in>,
        Alistair Delva <adelva@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH v2 3/4] Kbuild: make DWARF version a choice

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@...gle.com>
Suggested-by: Masahiro Yamada <masahiroy@...nel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.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