| Message ID | 20201201032748.486928-1-masahiroy@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Remove $(cc-option,-gdwarf-4) dependency from CONFIG_DEBUG_INFO_DWARF4 | expand |
On Tue, Dec 1, 2020 at 12:29 PM Masahiro Yamada <masahiroy@kernel.org> wrote: > > 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] > 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 > > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> > --- > > lib/Kconfig.debug | 1 - > 1 file changed, 1 deletion(-) > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index cb8ef4fd0d02..7f80c25497a1 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. > -- > 2.27. Maybe, this can be squashed into Nick's patch.
On Mon, Nov 30, 2020 at 7:42 PM Masahiro Yamada <masahiroy@kernel.org> wrote: > > On Tue, Dec 1, 2020 at 12:29 PM Masahiro Yamada <masahiroy@kernel.org> wrote: > > > > The -gdwarf-4 flag is supported by GCC 4.5+, and also by Clang. > > > > You can see it at https://godbolt.org/z/6ed1oW (this link misses -gdwarf-4 for clang, but I think that's ok) > > > > 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] > > 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 > > > > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> > > --- > > > > lib/Kconfig.debug | 1 - > > 1 file changed, 1 deletion(-) > > > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > > index cb8ef4fd0d02..7f80c25497a1 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. > > -- > > 2.27. > > > Maybe, this can be squashed into Nick's patch. I have no preference. Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> (I'll reroll this into my DWARFv5 series either way, but when/how you merge this doesn't matter to me)
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index cb8ef4fd0d02..7f80c25497a1 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.
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] 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 Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> --- lib/Kconfig.debug | 1 - 1 file changed, 1 deletion(-)