linux-kernel - [PATCH v2 0/5] fix debug info for asm and DEBUG_INFO

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Date:   Wed, 31 Aug 2022 11:44:03 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Michal Marek <michal.lkml@...kovi.net>,
        Nathan Chancellor <nathan@...nel.org>,
        Tom Rix <trix@...hat.com>, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev, x86@...nel.org,
        Dmitrii Bundin <dmitrii.bundin.a@...il.com>,
        Fangrui Song <maskray@...gle.com>,
        Alexey Alexandrov <aalexand@...gle.com>,
        Bill Wendling <morbo@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH v2 0/5] fix debug info for asm and DEBUG_INFO_SPLIT

Alexey reported that the fraction of unknown filename instances in
kallsyms grew from ~0.3% to ~10% recently; Bill and Greg tracked it down
to assembler defined symbols, which regressed as a result of:

commit b8a9092330da ("Kbuild: do not emit debug info for assembly with LLVM_IAS=1")

In that commit, I allude to restoring debug info for assembler defined
symbols in a follow up patch, but it seems I forgot to do so in

commit a66049e2cf0e ("Kbuild: make DWARF version a choice")

Do so requires a fixup for as-option, which seems to be failing when
used in scripts/Makefile.debug.

Also includes a fix for DEBUG_INFO_SPLIT while I'm here.  Dmitrii
reports that this has been broken since gcc-11+ & clang-12+. I'm
guessing no one uses this .config option...since no one else has
reported it being broken yet...

Changes from v1 -> v2:
* 5 patches now, rather than 3.
* Split change to arch/x86/boot/compressed/Makefile off of first patch,
  as per Masahiro.
* Introduce compiler specific macros, as per Bill, and eradicate
  cc-ifversion while I'm at it.
* Update commit message of final patch to refer to 866ced950bcd.

v1: https://lore.kernel.org/llvm/20220826181035.859042-1-ndesaulniers@google.com/


Nick Desaulniers (5):
  x86/boot/compressed: prefer cc-option for CFLAGS additions
  Makefile.compiler: Use KBUILD_AFLAGS for as-option
  Makefile.compiler: replace cc-ifversion with compiler-specific macros
  Makefile.debug: re-enable debug info for .S files
  Makefile.debug: set -g unconditional on CONFIG_DEBUG_INFO_SPLIT

 Documentation/kbuild/makefiles.rst          | 44 +++++++++++++++------
 Makefile                                    |  4 +-
 arch/x86/boot/compressed/Makefile           |  2 +-
 drivers/gpu/drm/amd/display/dc/dml/Makefile | 12 ++----
 scripts/Makefile.compiler                   | 21 +++++++---
 scripts/Makefile.debug                      | 26 ++++++++----
 6 files changed, 72 insertions(+), 37 deletions(-)

-- 
2.37.2.672.g94769d06f0-goog