On Fri, Jan 15, 2021 at 11:00 PM Fangrui Song <maskray@xxxxxxxxxx> wrote: > > On 2021-01-15, Nick Desaulniers wrote: > >From: Masahiro Yamada <masahiroy@xxxxxxxxxx> > > > >The -gdwarf-4 flag is supported by GCC 4.5+, and also by Clang. > > > >You can see it at https://godbolt.org/z/6ed1oW > > > > For gcc 4.5.3 pane, line 37: .value 0x4 > > For clang 10.0.1 pane, line 117: .short 4 > > > >Given Documentation/process/changes.rst stating GCC 4.9 is the minimal > >version, this cc-option is unneeded. > > > >Note > >---- > > > >CONFIG_DEBUG_INFO_DWARF4 controls the DWARF version only for C files. > > > >As you can see in the top Makefile, -gdwarf-4 is only passed to CFLAGS. > > > > ifdef CONFIG_DEBUG_INFO_DWARF4 > > DEBUG_CFLAGS += -gdwarf-4 > > endif > > > >This flag is used when compiling *.c files. > > > >On the other hand, the assembler is always given -gdwarf-2. > > > > KBUILD_AFLAGS += -Wa,-gdwarf-2 > > > >Hence, the debug info that comes from *.S files is always DWARF v2. > >This is simply because GAS supported only -gdwarf-2 for a long time. > > > >Recently, GAS gained the support for --dwarf-[3|4|5] options. [1] > > The gas commit description has a typo. The supported options are -gdwarf-[345] or --gdwarf-[345]. > -gdwarf2 and --gdwarf2 are kept for compatibility. > > Looks good otherwise. > Good catch Fangrui. Yesterday, I wondered - after a cut-n-paste from the patch's changelog - why I did not see anything --dwarfX related in my logs. - Sedat - > >And, also we have Clang integrated assembler. So, the debug info > >for *.S files might be improved if we want. > > > >In my understanding, the current code is intentional, not a bug. > > > >[1] https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=31bf18645d98b4d3d7357353be840e320649a67d > > > >Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > >Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx> > >Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx> > >--- > > lib/Kconfig.debug | 1 - > > 1 file changed, 1 deletion(-) > > > >diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > >index 78361f0abe3a..dd7d8d35b2a5 100644 > >--- a/lib/Kconfig.debug > >+++ b/lib/Kconfig.debug > >@@ -258,7 +258,6 @@ config DEBUG_INFO_SPLIT > > > > config DEBUG_INFO_DWARF4 > > bool "Generate dwarf4 debuginfo" > >- depends on $(cc-option,-gdwarf-4) > > help > > Generate dwarf4 debug info. This requires recent versions > > of gcc and gdb. It makes the debug information larger. > >-- > >2.30.0.284.gd98b1dd5eaa7-goog > >
