[PATCH v5 2/3] Kbuild: make DWARF version a choice

From: Nick Desaulniers <ndesaulniers@google.com>
To: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nathan Chancellor <natechancellor@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Sedat Dilek <sedat.dilek@gmail.com>,
	linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com,
	linux-kbuild@vger.kernel.org, linux-arch@vger.kernel.org,
	Jakub Jelinek <jakub@redhat.com>,
	Fangrui Song <maskray@google.com>,
	Caroline Tice <cmtice@google.com>,
	Nick Clifton <nickc@redhat.com>, Yonghong Song <yhs@fb.com>,
	Jiri Olsa <jolsa@kernel.org>, Andrii Nakryiko <andrii@kernel.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Arvind Sankar <nivedita@alum.mit.edu>
Subject: [PATCH v5 2/3] Kbuild: make DWARF version a choice
Date: Fri, 15 Jan 2021 13:06:15 -0800	[thread overview]
Message-ID: <20210115210616.404156-3-ndesaulniers@google.com> (raw)
In-Reply-To: <20210115210616.404156-1-ndesaulniers@google.com>

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 <nivedita@alum.mit.edu>
Suggested-by: Fangrui Song <maskray@google.com>
Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 Makefile          | 13 ++++++-------
 lib/Kconfig.debug | 21 ++++++++++++++++-----
 2 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/Makefile b/Makefile
index d49c3f39ceb4..4eb3bf7ee974 100644
--- a/Makefile
+++ b/Makefile
@@ -826,13 +826,12 @@ else
 DEBUG_CFLAGS	+= -g
 endif
 
-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)
+# Binutils 2.35+ required for -gdwarf-4+ support.
+dwarf-aflag	:= $(call as-option,-Wa$(comma)-gdwarf-$(dwarf-version-y))
+KBUILD_AFLAGS	+= $(dwarf-aflag)
 
 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 dd7d8d35b2a5..e80770fac4f0 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"
-- 
2.30.0.284.gd98b1dd5eaa7-goog

