I have a simple question about how can makefile read in a varibale is set in .config file.

for example i have CONFIG_a=y CONFIG_b and CONFIG_c as three variables in .config of my linux configuration . I have a Makefile which should define a variable depending upon which CONFIG_X is set

if CONFIG_A
DFLAGS=-DABC
if CONFIG_B
DFLAGS=-DBCD
if CONFIG_C
DFLAGS=-DCDE

How could i achieve this in make file.

I tried

ifeq ($(TARGET_A),y)
DFLAGS=-DABC
else
ifeq ($(TARGET_B),y)
DFLAGS=-DBCD
else
DFLAGS=-DCDE
endif
endif

THIS could not help each time -DCDE is set.

(Last edited by vikaspshinde on 25 Jun 2017, 07:25)

Please, take a look at Makefiles from packages feed, there's a bunch of examples.

I have seen this makefiles and also able to create my own make files but the case i want is not into this makefiles.

below are my two makefile.
1. for creating support for a target xyz

include $(TOPDIR)/rules.mk
PKG_NAME:=xyz
PKG_RELEASE:=1
PKG_VERSION:=2

TARGET_LIBS = -Wl,-Bstatic -lpthread
include $(INCLUDE_DIR)/package.mk

define Package/$(PKG_NAME)
  SECTION:=utils
  CATEGORY:=Utilities
  TITLE:= xyz
  DEPENDS:=@TARGET_ramips_rt305x_a||@TARGET_ramips_rt305x_b +libpthread +librt
endef
define Package/$(PKG_NAME)/description
This is a sample program for make
endef
define Build/Prepare
    mkdir -p $(PKG_BUILD_DIR)
    $(CP) ./src/* $(PKG_BUILD_DIR)/
    mkdir -p $(PKG_BUILD_DIR)/obj $(PKG_BUILD_DIR)/bin
endef
define Package/$(PKG_NAME)/Build/Configure
endef
define Package/$(PKG_NAME)/Build/Compile
    $(TARGET_CONFIGURE_OPTS) \
    CFLAGS="$(TARGET_CFLAGS)" \
    LDFLAGS="$(TARGET_LDFLAGS)" \
    LIBS="$(TARGET_LIBS)" \
    $(MAKE) -C $(PKG_BUILD_DIR) $(PKG_NAME)
endef

define Package/$(PKG_NAME)/install
   
    $(INSTALL_DIR) $(1)/usr/bin
    $(INSTALL_BIN) $(PKG_BUILD_DIR)/bin/$(PKG_NAME) $(1)/usr/bin/

endef
$(eval $(call BuildPackage,$(PKG_NAME)))

2nd make file is the makefile to compile the target

PKG_RELEASE:=0
PKG_VERSION:=2
IDIR=./inc
ODIR=./obj
BIN=./bin
SRC=./src
TARGET=xyz
CC=gcc
CFLAGS=-I$(IDIR) -lpthread -lrt -lm

DFLAGS=-DABC -DDEBUG

_SRC := $(shell ls $(SRC))

_DEPS := $(shell ls $(IDIR))
DEPS=$(_DEPS:%=$(IDIR)/%)

_OBJS=$(_SRC:%.c=%.o)
OBJS=$(_OBJS:%=$(ODIR)/%)

$(ODIR)/%.o: $(SRC)/%.c $(DEPS)
    $(CC) -c -Wall -o $@ $< $(CFLAGS) $(DFLAGS)

$(BIN)/$(TARGET): $(OBJS)
    $(CC) -Wall -o $@ $^ $(CFLAGS) $(DFLAGS)
   
all:    $(BIN)/$(TARGET)
clean:
    rm -rf $(BIN)/$(TARGET) $(ODIR)/*

My concern is that  in second makefile
if TARGET_ramips_rt305x_a is set to y then DFLAGS=-DABC -DDEBUG  has to be set before compiling
if TARGET_ramips_rt305x_b is set to y then DFLAGS=-DBCD -DDEBUG  has to be set before compiling

How can i do this?

config for linux kernel or packages ??
or maybe also for ARCH ?

For now the variable is for target profile and  it is used for packages. But it will be gratefull if u explain me for all three cases