DWARF5 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. Further -gdwarf-X where X is an unsupported value doesn't produce an error in $(CC). 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 5 | 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 Make CONFIG_DEBUG_INFO_DWARF4 part of a Kconfig choice to preserve forward compatibility. Link: http://www.dwarfstd.org/doc/DWARF5.pdf Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> --- RFC because this patch is super half baked, but I'm looking for feedback. I would logically split this into a series of patches; 1. disable -Wa,gdwarf-2 for LLVM_IAS=1, see also https://github.com/ClangBuiltLinux/linux/issues/716 https://github.com/ClangBuiltLinux/continuous-integration/blob/master/patches/llvm-all/linux-next/arm64/silence-dwarf2-warnings.patch that way we can backport for improved LLVM_IAS support. 2. move CONFIG_DEBUG_INFO_DWARF4 to choice. 3. implement the rest on top. I'm pretty sure GNU `as` only recently gained the ability to specify -gdwarf-4 without erroring in binutils 2.35, so that part likely needs to be fixed. Makefile | 19 ++++++++++++++++--- include/asm-generic/vmlinux.lds.h | 6 +++++- lib/Kconfig.debug | 29 +++++++++++++++++++++++++---- scripts/test_dwarf5_support.sh | 4 ++++ 4 files changed, 50 insertions(+), 8 deletions(-) create mode 100755 scripts/test_dwarf5_support.sh diff --git a/Makefile b/Makefile index e71979882e4f..0862df5b1a24 100644 --- a/Makefile +++ b/Makefile @@ -828,10 +828,23 @@ else DEBUG_CFLAGS += -g endif -KBUILD_AFLAGS += -Wa,-gdwarf-2 - +DWARF_VERSION=2 ifdef CONFIG_DEBUG_INFO_DWARF4 -DEBUG_CFLAGS += -gdwarf-4 +DWARF_VERSION=4 +endif +ifdef CONFIG_DEBUG_INFO_DWARF5 +DWARF_VERSION=5 +endif +DEBUG_CFLAGS += -gdwarf-$(DWARF_VERSION) + +ifneq ($(DWARF_VERSION)$(LLVM_IAS),21) +KBUILD_AFLAGS += -Wa,-gdwarf-$(DWARF_VERSION) +endif + +ifdef CONFIG_CC_IS_CLANG +ifneq ($(LLVM_IAS),1) +KBUILD_CFLAGS += -Wa,-gdwarf-$(DWARF_VERSION) +endif endif ifdef CONFIG_DEBUG_INFO_REDUCED diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index cd14444bf600..0382808ef9fe 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -828,7 +828,11 @@ .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 537cf3c2937d..6b01f0e2dad8 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -256,14 +256,35 @@ config DEBUG_INFO_SPLIT to know about the .dwo files and include them. Incompatible with older versions of ccache. +choice +prompt "DWARF version" + depends on DEBUG_INFO + default DEBUG_INFO_DWARF2 + help + Which version of DWARF debug info to emit. + +config DEBUG_INFO_DWARF2 + bool "Generate dwarf2 debuginfo" + help + Generate dwarf2 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 dwarf4 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. + +config DEBUG_INFO_DWARF5 + bool "Generate dwarf5 debuginfo" + depends on DEBUG_INFO + depends on $(success,$(srctree)/scripts/test_dwarf5_support.sh $(CC) $(CLANG_FLAGS)) + help + Genereate dwarf5 debug info. Requires binutils 2.35+, gcc 5.1+, and + gdb 8.0+. + +endchoice # "DWARF version" config DEBUG_INFO_BTF bool "Generate BTF typeinfo" diff --git a/scripts/test_dwarf5_support.sh b/scripts/test_dwarf5_support.sh new file mode 100755 index 000000000000..82c0eea45845 --- /dev/null +++ b/scripts/test_dwarf5_support.sh @@ -0,0 +1,4 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 +set -eu +echo ".file 0 \"asdf\"" | $* -Wa,-gdwarf-5 -c -x assembler -o /dev/null - -- 2.29.0.rc1.297.gfa9743e501-goog
