On Tue, Nov 03, 2020 at 04:53:42PM -0800, Nick Desaulniers wrote: > Modifies CONFIG_DEBUG_INFO_DWARF4 to be a member of a choice. Adds an > explicit CONFIG_DEBUG_INFO_DWARF2, which is the default. Does so in a > way that's forward compatible with existing configs, and makes adding > future versions more straightforward. > > Suggested-by: Fangrui Song <maskray@xxxxxxxxxx> > Suggested-by: Masahiro Yamada <masahiroy@xxxxxxxxxx> > Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > --- > Makefile | 14 ++++++++------ > lib/Kconfig.debug | 19 +++++++++++++++---- > 2 files changed, 23 insertions(+), 10 deletions(-) > > diff --git a/Makefile b/Makefile > index 75b1a3dcbf30..e23786a4c1c7 100644 > --- a/Makefile > +++ b/Makefile > @@ -826,12 +826,14 @@ else > DEBUG_CFLAGS += -g > endif > > -ifndef LLVM_IAS > -KBUILD_AFLAGS += -Wa,-gdwarf-2 > -endif > - > -ifdef CONFIG_DEBUG_INFO_DWARF4 > -DEBUG_CFLAGS += -gdwarf-4 > +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF2) := 2 > +dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4 > +DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y) > +ifneq ($(dwarf-version-y)$(LLVM_IAS),21) > +# Binutils 2.35+ required for -gdwarf-4+ support. > +dwarf-aflag := $(call as-option,-Wa$(comma)-gdwarf-$(dwarf-version-y)) > +DEBUG_CFLAGS += $(dwarf-aflag) > +KBUILD_AFLAGS += $(dwarf-aflag) > endif > For LLVM_IAS=1, adding dwarf-aflag to DEBUG_CFLAGS should not be necessary, no? This seems to add it for dwarf-4. The as-option check will only work on binutils 2.35.1 onwards: earlier versions will silently accept any -gdwarf-N option. Do we care? I think it'll just get dwarf-2 for assembly files even though dwarf-4 might have been configured. The earlier versions only error if the double-hyphen form --gdwarf-N is used. More generally, do we want to force this option via -Wa or should we leave it up to the compiler driver when we can? For both Clang/IAS and gcc/binutils, passing -gdwarf-N in KBUILD_AFLAGS will allow the compiler to pass on the appropriate option to the assembler (with gcc you only get --gdwarf-2 for the assembler except on trunk though). The only case that would absolutely require -Wa is Clang without IAS, might be worth adding the ability to pass on the flag to the external assembler? Btw, is -gsplit-dwarf at all useful for assembler files?
