Add debug option to Kconfig to enable debugging

This only disables optimizations for now, we should
be able to select more debug options from here.

it changes KBUILD_CFLAGS from  -Os to -O0.

Change-Id: I84515356f8af006b724d706c0647a671db54a6b5
Signed-off-by: Anas Nashif <anas.nashif@intel.com>

Makefile

@@ -364,10 +364,7 @@ ZEPHYRINCLUDE    := \
 
 KBUILD_CPPFLAGS := -DKERNEL
 
-DEFAULTFLAGS ?= -Os
-
 KBUILD_CFLAGS   := -c -g -std=c99 \
-		$(DEFAULTFLAGS) \
 		$(CONFIG_COMPILER_OPT) \
 		-fno-reorder-functions \
 		-fno-asynchronous-unwind-tables \
@@ -634,6 +631,12 @@ endif
 endif
 KBUILD_CFLAGS += $(stackp-flag)
 
+ifeq ($(CONFIG_DEBUG),y)
+KBUILD_CFLAGS  += -O0
+else
+KBUILD_CFLAGS  += -Os
+endif
+
 export x86_FLAGS arm_FLAGS arc_FLAGS LDFLAG_LINKERCMD OUTPUT_FORMAT OUTPUT_ARCH
 
 ARCHFLAGS = $($(SRCARCH)_FLAGS)

misc/Kconfig

@@ -58,6 +58,14 @@ config  KERNEL_BIN_NAME
 	default "microkernel" if MICROKERNEL
 	default "nanokernel" if NANOKERNEL
 
+config  DEBUG
+	bool "Build kernel with debugging"
+	default n
+	help
+	Build a kernel suitable for debugging.  Right now, this option
+	only disables optimization, more debugging variants can be selected
+	from here to allow more debugging.
+
 config  COMPILER_OPT
 	string
 	prompt "Custom compiler options"

scripts/Makefile.x86.preparch

@@ -1,9 +1,13 @@
+
+
 PERF_OPT_FLAG-y = -DPERF_OPT
 ALIGN_STACK_FLAG- = -mpreferred-stack-boundary=2
 SECTION_GC_FLAG = $(call cc-option,-ffunction-sections,) $(call cc-option,-fdata-sections,)
 LTO_FLAG-y = $(call cc-option,-flto,)
-PERF_OPT=$(if $(filter -Os,$(DEFAULTFLAGS)),,y)
+
+PERF_OPT=$(if $(filter -Os,$(KBUILD_CFLAGS)),,y)
 PERF_OPT_FLAG = $(PERF_OPT_FLAG-$(PERF_OPT))
+
 ALIGN_STACK_FLAG = $(ALIGN_STACK_FLAG-$(PERF_OPT))
 LTO_FLAG = $(LTO_FLAG-$(CONFIG_LTO))
 ifneq ($(CONFIG_PLATFORM_QUARK),y)