On Tue, Dec 1, 2020 at 5:45 AM 'Nick Desaulniers' via Clang Built Linux <clang-built-linux@xxxxxxxxxxxxxxxx> wrote: > > On Mon, Nov 30, 2020 at 10:05 AM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote: > > > > On Wed, Nov 4, 2020 at 9:53 AM 'Nick Desaulniers' via Clang Built > > Linux <clang-built-linux@xxxxxxxxxxxxxxxx> 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) > > > > This changes the behavior. > > > > For the Dwarf-2 case, > > > > Previously, -gdwarf-2 was passed to $(CC), > > so the debug info was generated by gcc. > > > > Now, -Wa,-gdwarf-2 is passed to $(CC). > > -gdwarf-2 is handled by GNU as. > > So, the source info points to /tmp/<hash>.s > > instead of the original .c file. > > > > > > > > Handling the Dwarf capability is very complicated. > > > > Are you still working for v3? > > Yes, I plan to revisit the series based on all of the feedback thus > far. Lately I'm focused on enabling LLVM_IAS=1 for Android; but I > would like to see this land so that the Linux kernel may provide > coverage and feedback to the toolchain developers for DWARF v5 (as > well as reduced binary image sizes). Maybe later this week I'll have > time to revisit. > -- > Thanks, > ~Nick Desaulniers > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@xxxxxxxxxxxxxxxx. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/CAKwvOdmPeOEA4dfODCKLE4A_M-SF5RBVFEf-NuiTkUTXAbh-5w%40mail.gmail.com. In my understanding, the complexity comes from the fact we are mixing up the $(CC) capability and $(AS) capability. They are orthogonal if I understand correctly. When building *.c files, the .debug* sections are generated by gcc (or clang), and embedded into the intermediate *.s files. The assembler (GAS or clang's IAS) simply transforms it into byte stream in *.o. So we do not care about the assembler capability. When building *.S files, the .debug* sections are generated by the assembler. Here, the assembler capability is important. Unless we use binutils 2.35+ or clang IAS, DWARF v2 is the only possible choice. So, we need two separate choices to handle this properly, I think. The following is the rough sketch. # The value is 2, 3, 4, or 5 depending on the assembler in use. # Unfortunately, we cannot check this by $(cc-option, -Wa,-gdwarf-4) # because GAS <= 2.34 accepts any -gdwarf-<N>. # readelf --debug-dump=info and grep or something? config AS_SUPPORTS_DWARF_VERSION int $(shell scripts/as_dwarf_support.sh) choice "DWARF version for C code debugging" config CC_DEBUG_INFO_DWARF2 bool "..." config CC_DEBUG_INFO_DWARF4 bool "..." config CC_DEBUG_INFO_DWARF5 bool "..." depends on GCC_VERSION >= 700000 || CC_IS_CLANG depends on AS_SUPPORTS_DWARF_VERSION >= 5 help gcc7+ or clang supports this. Unfortunately, we also need to check assembler capability because GAS <= 2.34 do not understand ".file 0" endchoice choice "DWARF version for assembly code debugging" config AS_DEBUG_INFO_DWARF2 bool "..." config AS_DEBUG_INFO_DWARF4 bool "..." depends on AS_SUPPORTS_DWARF_VERSION >= 4 config AS_DEBUG_INFO_DWARF5 bool "..." depends on AS_SUPPORTS_DWARF_VERSION >= 5 endchoice -- Best Regards Masahiro Yamada
