On Fri, Feb 5, 2021 at 9:22 PM Nick Desaulniers <ndesaulni...@google.com> wrote: > > DWARF v5 is the latest standard of the DWARF debug info format. > > DWARF5 wins significantly in terms of size and especially so when mixed > with compression (CONFIG_DEBUG_INFO_COMPRESSED). > > Link: http://www.dwarfstd.org/doc/DWARF5.pdf >
Accepted into mainline via kbuild-v5.12. - Sedat - [1] https://git.kernel.org/linus/6fbd6cf85a3be127454a1ad58525a3adcf8612ab > Patch 1 places the DWARF v5 sections explicitly in the kernel linker > script. > Patch 2 modifies Kconfig for DEBUG_INFO_DWARF4 to be used as a fallback. > Patch 3 adds an explicit Kconfig for DWARF v5 for clang and older GCC > where the implicit default DWARF version is not 5. > > Changes from v8: > * Separate out the linker script changes (from v7 0002). Put those > first. Carry Reviewed by and tested by tags. Least contentious part > of the series. Tagged for stable; otherwise users upgrading to GCC 11 > may find orphan section warnings from the implicit default DWARF > version changing and generating the new debug info sections. > * Add CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT in 0002, make it the > default rather than CONFIG_DEBUG_INFO_DWARF4, as per Mark, Jakub, > Arvind. > * Drop reviewed by and tested by tags for 0002 and 0003; sorry > reviewers/testers, but I view that as a big change. I will buy you > beers if you're fatigued, AND for the help so far. I appreciate you. > * Rework commit one lines, and commit messages somewhat. > * Remove Kconfig help text about v4 being "bigger." > * I didn't touch the BTF config from v8, but suggest the BTF folks > consider > > https://lore.kernel.org/bpf/20210111180609.713998-1-natechancel...@gmail.com/ > that way we can express via Kconfig that older version of pahole are > in conflict with other Kconfig options. > > Changes from v7: > (Strictly commit message changes) > * Pick up Nathan's reviewed by tags for both patches. > * Add note about only modifying compiler dwarf info, not assembler dwarf > info, as per Nathan. > * Add link to Red Hat bug report and Chris' reported by on patch 2. > * Add more info from Jakub on patch 2 commit message. > * Reorder info about validating version, noting the tree is not "clean" > in the sense that parts mess up existing CFLAGS, or don't use > DEBUG_CFLAGS. I will not be adding such cleanups to this series. They > can be done AFTER. > * Update note about 2.35.2 (rather than include the full text Jakub > wrote on it in > https://patchwork.kernel.org/project/linux-kbuild/patch/20201022012106.1875129-1-ndesaulni...@google.com/#23727667). > * Add note that GCC 11 has changed the implicit default version. > > Changes from v6: > * Reorder sections from linker script to match order from BFD's internal > linker script. > * Add .debug_names section, as per Fangrui. > * Drop CONFIG_DEBUG_INFO_DWARF2. Patch 0001 becomes a menu with 1 > choice. GCC's implicit default version of DWARF has been DWARF v4 > since ~4.8. > * Modify the test script to check for the presence of > https://sourceware.org/bugzilla/show_bug.cgi?id=27195. > * Drop the clang without integrated assembler block in > 0002. Bumps the version requirement for GAS to 2.35.2, which isn't > released yet (but should be released soon). Folks looking to test > with clang but without the integrated assembler should fetch > binutils-gdb, build it from source, add a symlink to > binutils-gdb/gas/as-new to binutils-gdb/gas/as, then prefix > binutils-gdb/gas/as to their $PATH when building the kernel. > > Changes from v5: > * Drop previous patch 1, it has been accepted into kbuild: > > https://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git/commit/?h=kbuild&id=3f4d8ce271c7082be75bacbcbd2048aa78ce2b44 > * Trying to set -Wa,-gdwarf-4 in the earlier patch was the source of > additional complexity. Drop it that part of the patch. We can revisit > clang without the integrated assembler setting -Wa,-gdwarf-4 later. > That is a separate problem from generally supporting DWARF v5. > * Rework the final patch for clang without the integrated assembler. > -Wa,-gdwarf-5 is required for DWARF5 in that case otherwise GAS will > not accept the assembler directives clang produces from C code when > generating asm. > > Changes from v4: > * drop set -e from script as per Nathan. > * add dependency on !CONFIG_DEBUG_INFO_BTF for DWARF v5 as per Sedat. > * Move LLVM_IAS=1 complexity from patch 2 to patch 3 as per Arvind and > Masahiro. Sorry it took me a few tries to understand the point (I > might still not), but it looks much cleaner this way. Sorry Nathan, I > did not carry forward your previous reviews as a result, but I would > appreciate if you could look again. > * Add Nathan's reviewed by tag to patch 1. > * Reword commit message for patch 3 to mention LLVM_IAS=1 and -gdwarf-5 > binutils addition later, and BTF issue. > * I still happen to see a pahole related error spew for the combination > of: > * LLVM=1 > * LLVM_IAS=1 > * CONFIG_DEBUG_INFO_DWARF4 > * CONFIG_DEBUG_INFO_BTF > Though they're non-fatal to the build. I'm not sure yet why removing > any one of the above prevents the warning spew. Maybe we'll need a v6. > > Changes from v3: > > Changes as per Arvind: > * only add -Wa,-gdwarf-5 for (LLVM=1|CC=clang)+LLVM_IAS=0 builds. > * add -gdwarf-5 to Kconfig shell script. > * only run Kconfig shell script for Clang. > > Apologies to Sedat and Nathan; I appreciate previous testing/review, but > I did no carry forward your Tested-by and Reviewed-by tags, as the > patches have changed too much IMO. > > Changes from v2: > * Drop two of the earlier patches that have been accepted already. > * Add measurements with GCC 10.2 to commit message. > * Update help text as per Arvind with help from Caroline. > * Improve case/wording between DWARF Versions as per Masahiro. > > Changes from the RFC: > * split patch in 3 patch series, include Fangrui's patch, too. > * prefer `DWARF vX` format, as per Fangrui. > * use spaces between assignment in Makefile as per Masahiro. > * simplify setting dwarf-version-y as per Masahiro. > * indent `prompt` in Kconfig change as per Masahiro. > * remove explicit default in Kconfig as per Masahiro. > * add comments to test_dwarf5_support.sh. > * change echo in test_dwarf5_support.sh as per Masahiro. > * remove -u from test_dwarf5_support.sh as per Masahiro. > * add a -gdwarf-5 cc-option check to Kconfig as per Jakub. > > Nick Desaulniers (3): > vmlinux.lds.h: add DWARF v5 sections > Kbuild: make DWARF version a choice > Kconfig: allow explicit opt in to DWARF v5 > > Makefile | 6 ++-- > include/asm-generic/vmlinux.lds.h | 7 ++++- > lib/Kconfig.debug | 48 +++++++++++++++++++++++++++---- > scripts/test_dwarf5_support.sh | 8 ++++++ > 4 files changed, 61 insertions(+), 8 deletions(-) > create mode 100755 scripts/test_dwarf5_support.sh > > -- > 2.30.0.365.g02bc693789-goog >
