linux-kernel - [PATCH v7 1/2] Kbuild: make DWARF version a choice

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Message-Id: <20210130004401.2528717-2-ndesaulniers@google.com>
Date:   Fri, 29 Jan 2021 16:44:00 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sedat Dilek <sedat.dilek@...il.com>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        linux-kbuild@...r.kernel.org, linux-arch@...r.kernel.org,
        Jakub Jelinek <jakub@...hat.com>,
        Fangrui Song <maskray@...gle.com>,
        Caroline Tice <cmtice@...gle.com>,
        Nick Clifton <nickc@...hat.com>, Yonghong Song <yhs@...com>,
        Jiri Olsa <jolsa@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH v7 1/2] Kbuild: make DWARF version a choice

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

GCC since ~4.8 has defaulted to this DWARF version implicitly.

Suggested-by: Arvind Sankar <nivedita@...m.mit.edu>
Suggested-by: Fangrui Song <maskray@...gle.com>
Suggested-by: Nathan Chancellor <nathan@...nel.org>
Suggested-by: Masahiro Yamada <masahiroy@...nel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
 Makefile          |  5 ++---
 lib/Kconfig.debug | 16 +++++++++++-----
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/Makefile b/Makefile
index 95ab9856f357..d2b4980807e0 100644
--- a/Makefile
+++ b/Makefile
@@ -830,9 +830,8 @@ ifneq ($(LLVM_IAS),1)
 KBUILD_AFLAGS	+= -Wa,-gdwarf-2
 endif
 
-ifdef CONFIG_DEBUG_INFO_DWARF4
-DEBUG_CFLAGS	+= -gdwarf-4
-endif
+dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
+DEBUG_CFLAGS	+= -gdwarf-$(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..94c1a7ed6306 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -256,13 +256,19 @@ 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_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