On Wed, Aug 31, 2022 at 11:44:07AM -0700, Nick Desaulniers wrote:
> 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")
>
> This patch does a few things:
> 1. Add -g to KBUILD_AFLAGS. This will instruct the compiler to instruct
> the assembler to emit debug info. But this can cause an issue for
> folks using a newer compiler but older assembler, because the
> implicit default DWARF version changed from v4 to v5 in gcc-11 and
> clang-14.
> 2. If the user is using CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT, use a
> version check to explicitly set -Wa,-gdwarf-<version> for the
> assembler. There's another problem with this; GAS only gained support
> for explicit DWARF versions 3-5 in the 2.36 GNU binutils release.
> 3. Wrap -Wa,-gdwarf-<version> in as-option call to test whether the
> assembler supports that explicit DWARF version.
>
> Link: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=31bf18645d98b4d3d7357353be840e320649a67d
> Fixes: b8a9092330da ("Kbuild: do not emit debug info for assembly with LLVM_IAS=1")
> Reported-by: Alexey Alexandrov <aalexand@xxxxxxxxxx>
> Reported-by: Bill Wendling <morbo@xxxxxxxxxx>
> Reported-by: Greg Thelen <gthelen@xxxxxxxxxx>
> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> ---
> Changes v1 -> v2:
> * Use newly added compiler-specific macros, as per Bill.
>
> scripts/Makefile.debug | 22 ++++++++++++++++++----
> 1 file changed, 18 insertions(+), 4 deletions(-)
>
> diff --git a/scripts/Makefile.debug b/scripts/Makefile.debug
> index 9f39b0130551..46e88f0ca998 100644
> --- a/scripts/Makefile.debug
> +++ b/scripts/Makefile.debug
> @@ -4,18 +4,32 @@ ifdef CONFIG_DEBUG_INFO_SPLIT
> DEBUG_CFLAGS += -gsplit-dwarf
> else
> DEBUG_CFLAGS += -g
> +KBUILD_AFLAGS += -g
> endif
>
> -ifndef CONFIG_AS_IS_LLVM
> -KBUILD_AFLAGS += -Wa,-gdwarf-2
> +ifdef CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
> +# gcc-11+, clang-14+
> +ifeq ($(call cc-min-version, 110000, 140000),y)
> +dwarf-version-y := 5
> +else
> +dwarf-version-y := 4
> endif
> -
> -ifndef CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
> +else # !CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT
> dwarf-version-$(CONFIG_DEBUG_INFO_DWARF4) := 4
> dwarf-version-$(CONFIG_DEBUG_INFO_DWARF5) := 5
> DEBUG_CFLAGS += -gdwarf-$(dwarf-version-y)
> endif
>
> +# Binutils 2.35+ (or clang) required for -gdwarf-{4|5}.
> +# https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=31bf18645d98b4d3d7357353be840e320649a67d
> +ifneq ($(call as-option,-Wa$(comma)-gdwarf-$(dwarf-version-y)),)
> +KBUILD_AFLAGS += -Wa,-gdwarf-$(dwarf-version-y)
> +else
> +ifndef CONFIG_AS_IS_LLVM
> +KBUILD_AFLAGS += -Wa,-gdwarf-2
> +endif
> +endif
> +
> ifdef CONFIG_DEBUG_INFO_REDUCED
> DEBUG_CFLAGS += -fno-var-tracking
> ifdef CONFIG_CC_IS_GCC
> --
> 2.37.2.672.g94769d06f0-goog
>
