[PATCH v2 0/4] Kbuild: DWARF v5 support

[Nick Desaulniers]

DWARF v5 is the latest standard of the DWARF debug info format.

DWARF5 wins significantly in terms of size when mixed with compression
(CONFIG_DEBUG_INFO_COMPRESSED).

Link: http://www.dwarfstd.org/doc/DWARF5.pdf

Patch 1 is a fixup already sent, but necessary for trying to use
LLVM_IAS=1 with ToT LLVM.
https://lore.kernel.org/stable/20201103012358.168682-1-maskray@xxxxxxxxxx/

Patches 2 and 3 are cleanups that lay the ground work and aren't DWARF
v5 specific. In particular, I would like to see Patch 2 sent to stable
so that Android and CrOS can move to LLVM_IAS=1 ASAP.

Patch 4 implements Kconfig and Kbuild support for DWARFv5.

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.

Fangrui Song (1):
  x86_64: Change .weak to SYM_FUNC_START_WEAK for arch/x86/lib/mem*_64.S

Nick Desaulniers (3):
  Kbuild: do not emit debug info for assembly with LLVM_IAS=1
  Kbuild: make DWARF version a choice
  Kbuild: implement support for DWARF v5

 Makefile                          | 13 +++++++++----
 arch/x86/lib/memcpy_64.S          |  4 +---
 arch/x86/lib/memmove_64.S         |  4 +---
 arch/x86/lib/memset_64.S          |  4 +---
 include/asm-generic/vmlinux.lds.h |  6 +++++-
 lib/Kconfig.debug                 | 27 +++++++++++++++++++++++----
 scripts/test_dwarf5_support.sh    |  9 +++++++++
 7 files changed, 49 insertions(+), 18 deletions(-)
 create mode 100755 scripts/test_dwarf5_support.sh

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2.29.1.341.ge80a0c044ae-goog