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. 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. GNU `as` only recently gained support for specifying -gdwarf-5, so when compiling with Clang but without Clang's integrated assembler (LLVM_IAS=1 is not set), explicitly add -Wa,-gdwarf-5 to DEBUG_CFLAGS. Disabled for now if CONFIG_DEBUG_INFO_BTF is set; pahole doesn't yet recognize the new additions to the DWARF debug info. Thanks to Sedat for the report. Link: http://www.dwarfstd.org/doc/DWARF5.pdf Reported-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> Suggested-by: Arvind Sankar <nivedita@xxxxxxxxxxxx> Suggested-by: Caroline Tice <cmtice@xxxxxxxxxx> Suggested-by: Fangrui Song <maskray@xxxxxxxxxx> Suggested-by: Jakub Jelinek <jakub@xxxxxxxxxx> Suggested-by: Masahiro Yamada <masahiroy@xxxxxxxxxx> Suggested-by: Nathan Chancellor <natechancellor@xxxxxxxxx> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> --- Makefile | 12 ++++++++++++ include/asm-generic/vmlinux.lds.h | 6 +++++- lib/Kconfig.debug | 18 ++++++++++++++++++ scripts/test_dwarf5_support.sh | 8 ++++++++ 4 files changed, 43 insertions(+), 1 deletion(-) create mode 100755 scripts/test_dwarf5_support.sh diff --git a/Makefile b/Makefile index 20141cd9319e..bed8b3b180b8 100644 --- a/Makefile +++ b/Makefile @@ -832,8 +832,20 @@ 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) +# If using clang without the integrated assembler, we need to explicitly tell +# GAS that we will be feeding it DWARF v5 assembler directives. Kconfig should +# detect whether the version of GAS supports DWARF v5. +ifdef CONFIG_CC_IS_CLANG +ifneq ($(LLVM_IAS),1) +ifeq ($(dwarf-version-y),5) +DEBUG_CFLAGS += -Wa,-gdwarf-5 +endif +endif +endif + ifdef CONFIG_DEBUG_INFO_REDUCED DEBUG_CFLAGS += $(call cc-option, -femit-struct-debug-baseonly) \ $(call cc-option,-fno-var-tracking) diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 34b7e0d2346c..f8d5455cd87f 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 1850728b23e6..09146b1af20d 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -273,6 +273,24 @@ 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)) + depends on !DEBUG_INFO_BTF + 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..1a00484d0b2e --- /dev/null +++ b/scripts/test_dwarf5_support.sh @@ -0,0 +1,8 @@ +#!/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 +echo '.file 0 "filename"' | $* -gdwarf-5 -Wa,-gdwarf-5 -c -x assembler -o /dev/null - -- 2.30.0.365.g02bc693789-goog
