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>,
Nick Desaulniers <ndesaulniers@google.com>,
Arvind Sankar <nivedita@alum.mit.edu>
Subject: [PATCH v4 3/3] Kbuild: implement support for DWARF v5
Date: Tue, 12 Jan 2021 16:32:35 -0800 [thread overview]
Message-ID: <20210113003235.716547-4-ndesaulniers@google.com> (raw)
In-Reply-To: <20210113003235.716547-1-ndesaulniers@google.com>
DWARF v5 is the latest standard of the DWARF debug info format.
Feature detection of DWARF5 is onerous, especially given that we've
removed $(AS), so we must query $(CC) for DWARF5 assembler directive
support. GNU `as` only recently gained support for specifying
-gdwarf-5.
The DWARF version of a binary can be validated with:
$ llvm-dwarfdump vmlinux | head -n 4 | grep version
or
$ readelf --debug-dump=info vmlinux 2>/dev/null | grep Version
DWARF5 wins significantly in terms of size when mixed with compression
(CONFIG_DEBUG_INFO_COMPRESSED).
363M vmlinux.clang12.dwarf5.compressed
434M vmlinux.clang12.dwarf4.compressed
439M vmlinux.clang12.dwarf2.compressed
457M vmlinux.clang12.dwarf5
536M vmlinux.clang12.dwarf4
548M vmlinux.clang12.dwarf2
515M vmlinux.gcc10.2.dwarf5.compressed
599M vmlinux.gcc10.2.dwarf4.compressed
624M vmlinux.gcc10.2.dwarf2.compressed
630M vmlinux.gcc10.2.dwarf5
765M vmlinux.gcc10.2.dwarf4
809M vmlinux.gcc10.2.dwarf2
Though the quality of debug info is harder to quantify; size is not a
proxy for quality.
Jakub notes:
All [GCC] 5.1 - 6.x did was start accepting -gdwarf-5 as experimental
option that enabled some small DWARF subset (initially only a few
DW_LANG_* codes newly added to DWARF5 drafts). Only GCC 7 (released
after DWARF 5 has been finalized) started emitting DWARF5 section
headers and got most of the DWARF5 changes in...
Version check GCC so that we don't need to worry about the difference in
command line args between GNU readelf and llvm-readelf/llvm-dwarfdump to
validate the DWARF Version in the assembler feature detection script.
Link: http://www.dwarfstd.org/doc/DWARF5.pdf
Suggested-by: Arvind Sankar <nivedita@alum.mit.edu>
Suggested-by: Jakub Jelinek <jakub@redhat.com>
Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Suggested-by: Fangrui Song <maskray@google.com>
Suggested-by: Caroline Tice <cmtice@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
Makefile | 1 +
include/asm-generic/vmlinux.lds.h | 6 +++++-
lib/Kconfig.debug | 17 +++++++++++++++++
scripts/test_dwarf5_support.sh | 9 +++++++++
4 files changed, 32 insertions(+), 1 deletion(-)
create mode 100755 scripts/test_dwarf5_support.sh
diff --git a/Makefile b/Makefile
index 656fff17b331..1067cfd98249 100644
--- a/Makefile
+++ b/Makefile
@@ -828,6 +828,7 @@ endif
dwarf-version-$(CONFIG_DEBUG_INFO_DWARF2) := 2
dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
+dwarf-version-$(CONFIG_DEBUG_INFO_DWARF5) := 5
DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y)
ifneq ($(dwarf-version-y)$(LLVM_IAS),21)
# Binutils 2.35+ required for -gdwarf-4+ support.
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 49944f00d2b3..37dc4110875e 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -843,7 +843,11 @@
.debug_types 0 : { *(.debug_types) } \
/* DWARF 5 */ \
.debug_macro 0 : { *(.debug_macro) } \
- .debug_addr 0 : { *(.debug_addr) }
+ .debug_addr 0 : { *(.debug_addr) } \
+ .debug_line_str 0 : { *(.debug_line_str) } \
+ .debug_loclists 0 : { *(.debug_loclists) } \
+ .debug_rnglists 0 : { *(.debug_rnglists) } \
+ .debug_str_offsets 0 : { *(.debug_str_offsets) }
/* Stabs debugging sections. */
#define STABS_DEBUG \
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index e80770fac4f0..60a4f5e27ada 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -273,6 +273,23 @@ config DEBUG_INFO_DWARF4
It makes the debug information larger, but it significantly
improves the success of resolving variables in gdb on optimized code.
+config DEBUG_INFO_DWARF5
+ bool "Generate DWARF Version 5 debuginfo"
+ depends on GCC_VERSION >= 50000 || CC_IS_CLANG
+ depends on CC_IS_GCC || $(success,$(srctree)/scripts/test_dwarf5_support.sh $(CC) $(CLANG_FLAGS))
+ help
+ Generate DWARF v5 debug info. Requires binutils 2.35, gcc 5.0+ (gcc
+ 5.0+ accepts the -gdwarf-5 flag but only had partial support for some
+ draft features until 7.0), and gdb 8.0+.
+
+ Changes to the structure of debug info in Version 5 allow for around
+ 15-18% savings in resulting image and debug info section sizes as
+ compared to DWARF Version 4. DWARF Version 5 standardizes previous
+ extensions such as accelerators for symbol indexing and the format
+ for fission (.dwo/.dwp) files. Users may not want to select this
+ config if they rely on tooling that has not yet been updated to
+ support DWARF Version 5.
+
endchoice # "DWARF version"
config DEBUG_INFO_BTF
diff --git a/scripts/test_dwarf5_support.sh b/scripts/test_dwarf5_support.sh
new file mode 100755
index 000000000000..142a1b5c7fa2
--- /dev/null
+++ b/scripts/test_dwarf5_support.sh
@@ -0,0 +1,9 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+# Test that assembler accepts -gdwarf-5 and .file 0 directives, which were bugs
+# in binutils < 2.35.
+# https://sourceware.org/bugzilla/show_bug.cgi?id=25612
+# https://sourceware.org/bugzilla/show_bug.cgi?id=25614
+set -e
+echo '.file 0 "filename"' | $* -gdwarf-5 -Wa,-gdwarf-5 -c -x assembler -o /dev/null -
--
2.30.0.284.gd98b1dd5eaa7-goog
next prev parent reply other threads:[~2021-01-13 0:46 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-13 0:32 [PATCH v4 0/3] Kbuild: DWARF v5 support Nick Desaulniers
2021-01-13 0:32 ` [PATCH v4 1/3] Remove $(cc-option,-gdwarf-4) dependency from CONFIG_DEBUG_INFO_DWARF4 Nick Desaulniers
2021-01-13 17:48 ` Nathan Chancellor
2021-01-13 0:32 ` [PATCH v4 2/3] Kbuild: make DWARF version a choice Nick Desaulniers
2021-01-13 17:51 ` Nathan Chancellor
2021-01-13 21:24 ` Sedat Dilek
2021-01-13 23:27 ` Nick Desaulniers
2021-01-14 7:20 ` Sedat Dilek
2021-01-14 7:30 ` Sedat Dilek
2021-01-15 3:54 ` Masahiro Yamada
2021-01-13 0:32 ` Nick Desaulniers [this message]
2021-01-13 17:55 ` [PATCH v4 3/3] Kbuild: implement support for DWARF v5 Nathan Chancellor
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