how to add Zephyr include directories to external library which's using different build system

[wentongwu]

Describe the bug
The example samples/application_development/external_lib demonstrates how to include an external static library
using a different build system into the Zephyr build system.
But sometimes the external library code(using different build system) needs some functions from Zephyr, that means when building the external static library with its own building system, it also needs Zephyr's include directories if we don't want to add lots of extern in the external library code. Is there any good way to handle this case? Thanks!

[wentongwu]

@SebastianBoe @tejlmand

[wentongwu]

@nashif

[tejlmand]

@wentongwu you can use the zephyr_generated_headers build target.

Enable: CONFIG_MAKEFILE_EXPORTS=y, and build your sample.

As example when running CMake:

cmake ... -DCONFIG_MAKEFILE_EXPORTS=y <sample>

and then you can produce files containing build setting as:

$ ninja zephyr_generated_headers

or

$ make zephyr_generated_headers

which will produce:

$ ls Makefile.exports.*
Makefile.exports.ASM
Makefile.exports.C
Makefile.exports.CXX

with content like:

CC = /opt/zephyr-sdk-0.12.0-beta/arm-zephyr-eabi/bin/arm-zephyr-eabi-gcc
CXX = /opt/zephyr-sdk-0.12.0-beta/arm-zephyr-eabi/bin/arm-zephyr-eabi-g++
OBJCOPY = /opt/zephyr-sdk-0.12.0-beta/arm-zephyr-eabi/bin/arm-zephyr-eabi-objcopy
OBJDUMP = /opt/zephyr-sdk-0.12.0-beta/arm-zephyr-eabi/bin/arm-zephyr-eabi-objdump
AS = /opt/zephyr-sdk-0.12.0-beta/arm-zephyr-eabi/bin/arm-zephyr-eabi-as
AR = /opt/zephyr-sdk-0.12.0-beta/arm-zephyr-eabi/bin/arm-zephyr-eabi-ar
NM = /opt/zephyr-sdk-0.12.0-beta/arm-zephyr-eabi/bin/arm-zephyr-eabi-nm
GDB = /opt/zephyr-sdk-0.12.0-beta/arm-zephyr-eabi/bin/arm-zephyr-eabi-gdb
Z_CFLAGS = -I/projects/github/ncs/zephyr/include -I/projects/github/ncs/zephyr/build/zephyr/include/generated .....

[wentongwu]

@tejlmand Nice! Thanks!

[wentongwu]

and I'm trying to make a patch like below for this sample, but is there a way to know the board and project dir which are already in CMake file? Thanks in advance! @tejlmand

diff --git a/samples/application_development/external_lib/mylib/Makefile b/samples/application_development/external_lib/mylib/Makefile
index 846407cfdf..7654bde86c 100644
--- a/samples/application_development/external_lib/mylib/Makefile
+++ b/samples/application_development/external_lib/mylib/Makefile
@@ -7,11 +7,20 @@
 PREFIX ?= .
 OBJ_DIR ?= $(PREFIX)/obj
 LIB_DIR ?= $(PREFIX)/lib
+TMP_DIR ?= $(PREFIX)/tmp

-all:
+include $(TMP_DIR)/Makefile.exports.C
+
+zephyr_headers:
+       rm -rf $(TMP_DIR) && mkdir -p $(TMP_DIR) && cd $(TMP_DIR)
+       cmake -DBOARD=board -DCONFIG_MAKEFILE_EXPORTS=y project_dir
+       make zephyr_generated_headers
+       cd -
+
+all: zephyr_headers
        mkdir -p $(OBJ_DIR) $(LIB_DIR)
-       $(CC) -c $(CFLAGS) -MD -Iinclude src/mylib.c -o $(OBJ_DIR)/mylib.o
+       $(CC) -c $(CFLAGS) $(Z_CFLAGS) -MD -Iinclude src/mylib.c -o $(OBJ_DIR)/mylib.o
        $(AR) -rcs $(LIB_DIR)/libmylib.a $(OBJ_DIR)/mylib.o

 clean:
-       rm -rf $(OBJ_DIR) $(LIB_DIR)
+       rm -rf $(OBJ_DIR) $(LIB_DIR) $(TMP_DIR)
diff --git a/samples/application_development/external_lib/mylib/src/mylib.c b/samples/application_development/external_lib/mylib/src/mylib.c
index 3f18508c35..2dd6494605 100644
--- a/samples/application_development/external_lib/mylib/src/mylib.c
+++ b/samples/application_development/external_lib/mylib/src/mylib.c
@@ -6,6 +6,7 @@

 #include "mylib.h"
 #include <stdio.h>
+#include <zephyr.h>

 int mylib_hello_world(void)
 {

[tejlmand]

you can extend the zephyr_generated_headers target, like this:

diff --git a/cmake/makefile_exports/CMakeLists.txt b/cmake/makefile_exports/CMakeLists.txt
index 3255ffe041..b1029866b5 100644
--- a/cmake/makefile_exports/CMakeLists.txt
+++ b/cmake/makefile_exports/CMakeLists.txt
@@ -8,6 +8,8 @@ zephyr_get_compile_options_for_lang_as_string(CXX CXX_compile_options)
 
 set(exports
   "
+BOARD = ${BOARD}
+PROJ_DIR = ${APPLICATION_SOURCE_DIR}
 CC = ${CMAKE_C_COMPILER}
 CXX = ${CMAKE_CXX_COMPILER}
 OBJCOPY = ${CMAKE_OBJCOPY}

will give you the following in addition:

$ cat Makefile.exports.C

BOARD = em_starterkit
PROJ_DIR = /projects/github/ncs/zephyr/samples/hello_world
CC = /opt/zephyr-sdk-0.12.0-beta/arc-zephyr-elf/bin/arc-zephyr-elf-gcc
.....

[wentongwu]

@tejlmand thanks