Re: [PATCH] kbuild: Disable extra debugging info in .s output

Masahiro Yamada
2019-02-10T06:51:42Z

On Wed, Feb 6, 2019 at 7:49 PM Borislav Petkov <bp@alien8.de> wrote:
>
> On Sat, Feb 02, 2019 at 03:42:27PM +0100, Borislav Petkov wrote:
> > On Sat, Feb 02, 2019 at 10:48:00PM +0900, Masahiro Yamada wrote:
> > > '?=' is the same as '=' here.
> >
> > Sure but if the slowdown disappears, then make does something else for
> > '?=' apparently vs for '='.

'=' and '?=' are the same in the sense that
the right-hand side is evaluated when it is used.

> Ok, let me ask a different question then: would a separate target which
> will be used to generate only clean asm for debugging purposes ala
>
> make <path-to-file>.asm

Sorry, I do not like to duplicate the code.

I do not understand why you need to test such complicated
compiler flags in order to negate CONFIG_DEBUG_INFO.

I am still wondering,
but if this is really worth doing in upstream code,
I think the following is a simpler idea.

diff --git a/Makefile b/Makefile
index 3142e67..131164a 100644
--- a/Makefile
+++ b/Makefile
@@ -729,25 +729,28 @@ KBUILD_CFLAGS += -fomit-frame-pointer
endif
endif

-KBUILD_CFLAGS += $(call cc-option, -fno-var-tracking-assignments)
+DEBUG_CFLAGS := $(call cc-option, -fno-var-tracking-assignments)

ifdef CONFIG_DEBUG_INFO
ifdef CONFIG_DEBUG_INFO_SPLIT
-KBUILD_CFLAGS += $(call cc-option, -gsplit-dwarf, -g)
+DEBUG_CFLAGS += $(call cc-option, -gsplit-dwarf, -g)
else
-KBUILD_CFLAGS += -g
+DEBUG_CFLAGS += -g
endif
KBUILD_AFLAGS += -Wa,-gdwarf-2
endif
ifdef CONFIG_DEBUG_INFO_DWARF4
-KBUILD_CFLAGS += $(call cc-option, -gdwarf-4,)
+DEBUG_CFLAGS += $(call cc-option, -gdwarf-4,)
endif

ifdef CONFIG_DEBUG_INFO_REDUCED
-KBUILD_CFLAGS += $(call cc-option, -femit-struct-debug-baseonly) \
+DEBUG_CFLAGS += $(call cc-option, -femit-struct-debug-baseonly) \
$(call cc-option,-fno-var-tracking)
endif

+KBUILD_CFLAGS += $(DEBUG_CFLAGS)
+export DEBUG_CFLAGS
+
ifdef CONFIG_FUNCTION_TRACER
ifdef CONFIG_FTRACE_MCOUNT_RECORD
# gcc 5 supports generating the mcount tables directly

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index fd03d60..bc8e0ae 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -104,7 +104,7 @@ modkern_cflags = \
quiet_modtag = $(if $(part-of-module),[M], )

quiet_cmd_cc_s_c = CC $(quiet_modtag) $@
-cmd_cc_s_c = $(CC) $(c_flags) $(DISABLE_LTO) -fverbose-asm -S -o $@ $<
+cmd_cc_s_c = $(CC) $(filter-out $(DEBUG_CFLAGS), $(c_flags))
$(DISABLE_LTO) -fverbose-asm -S -o $@ $<

$(obj)/%.s: $(src)/%.c FORCE
$(call if_changed_dep,cc_s_c)

> or so be an acceptable approach?
>
> Thx.
>
> --
> Regards/Gruss,
> Boris.
>
> Good mailing practices for 400: avoid top-posting and trim the reply.

--
Best Regards
Masahiro Yamada