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[Solved, more or less] OpenWRT C++ CrossCompile uClibc setup

  • Hiho,
    I want to compile a "helloWorld"-package with the openwrt standart setup found on: https://github.com/OnionIoT/OpenWRT-Packages/wiki/Setting-Up-the-Cross-Compile-Environment

    The problem is, that with this setup a normal program links dynamically against: "ld-musl-mips-sf.so.1" but the onion has "ld-uClibc.so.0" installed. I know that a static linked program works, but in the end I don't want to get hello World to work šŸ˜‰

    $ readelf -l helloWorld
    Elf file type is EXEC (Executable file)
    Entry point 0x400600
    There are 9 program headers, starting at offset 52
    Program Headers:
      Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
      PHDR           0x000034 0x00400034 0x00400034 0x00120 0x00120 R E 0x4
      INTERP         0x000154 0x00400154 0x00400154 0x0001a 0x0001a R   0x1
          [Requesting program interpreter: /lib/ld-musl-mips-sf.so.1]
      REGINFO        0x000170 0x00400170 0x00400170 0x00018 0x00018 R   0x4
      LOAD           0x000000 0x00400000 0x00400000 0x008f0 0x008f0 R E 0x10000
      LOAD           0x000fdc 0x00410fdc 0x00410fdc 0x00050 0x00074 RW  0x10000
      DYNAMIC        0x000188 0x00400188 0x00400188 0x00110 0x00110 RWE 0x4
      GNU_STACK      0x000000 0x00000000 0x00000000 0x00000 0x00000 RW  0x10
      GNU_RELRO      0x000fdc 0x00410fdc 0x00410fdc 0x00024 0x00024 R   0x1
      NULL           0x000000 0x00000000 0x00000000 0x00000 0x00000     0x4
     Section to Segment mapping:
      Segment Sections...
       01     .interp 
       02     .reginfo 
       03     .interp .reginfo .dynamic .hash .dynsym .dynstr .gnu.version .gnu.version_r .rel.plt .init .text .MIPS.stubs .fini .rodata .eh_frame .plt 
       04     .ctors .dtors .got.plt .rld_map .got .sdata .bss 
       05     .dynamic 
       07     .ctors .dtors .got.plt 

    After reading "https://community.onion.io/topic/9/how-to-install-gcc" I believe that this dynamic link is what caused the problem for Kit Bishop:

    root@Omega:~# ls -l
    -rwxrwxrwx    1 root     root          8994 Nov 18 12:26 testc
    root@Omega:~# ./testc
    -ash: ./testc: not found

    (Sry but I can't find a link to his post option :-()

    I see that the tool chain uses the wrong stdLib, that path name of the tool chain looks like: "...toolchain-mips_34kc_gcc-5.2.0_musl-1.1.11/

    I have the kernel settings on "Preferred standard C++ library (uClibc++) --->" but the other uClibc settings I can't activate because mips is set and I don't know where openwrt configures the tool chain std lib.

    So the question is: How to configure the openwrt setup to compile programs for the existing onion os? How to use uClibc instead of musl?

    Just for completness here are my helloWorld Makefile:

    # build helloworld executable when user executes "make"
    helloWorld: helloWorld.o
    	@echo "\n\n----------------------\n\n"
    	@echo "CXX: $(CXX)"
    	@echo "CFLAGS: $(CFLAGS)"
    	@echo "LDFLAGS: $(LDFLAGS)"
    	@echo "LIB: $(LIB)"
    	$(CXX) $(LDFLAGS) helloWorld.o -o helloWorld
    helloWorld.o: helloWorld.c
    	$(CXX) $(CXXFLAGS) -c helloWorld.c
    all: helloWorld
    	rm *.o helloWorld

    and the openWRT project Makefile:

    include $(TOPDIR)/rules.mk
    # This specifies the directory where we're going to build the program.  
    # The root build directory, $(BUILD_DIR), is by default the build_mipsel 
    # directory in your OpenWrt SDK directory
    include $(INCLUDE_DIR)/package.mk 
    define Package/helloWorld
    define Package/helloWorld/description
    	Hello World
    # Specify what needs to be done to prepare for building the package.
    # In our case, we need to copy the source files to the build directory.
    # This is NOT the default.  The default uses the PKG_SOURCE_URL and the
    # PKG_SOURCE which is not defined here to download the source from the web.
    # In order to just build a simple program that we have just written, it is
    # much easier to do it this way.
    define Build/Prepare
    	mkdir -p $(PKG_BUILD_DIR)
    	$(CP) /home/apit/projects/openwrt/helloWorld/* $(PKG_BUILD_DIR)/
    MAKE_OPTS:= \
        ARCH="$(LINUX_KARCH)" \
    define Package/helloWorld/Compile
    	cd $(PKG_BUILD_DIR)
    	#$(MAKE) -C $(PKG_BUILD_DIR) \
    	#	CXXFLAGS="$(TARGET_CFLAGS) $(EXTRA_CPPFLAGS) -nostdinc++" \
    	#	CROSS="$(TARGET_CROSS)" \
    	#	ARCH="$(ARCH)" \
    	#	$(1);
    define Package/helloWorld/install
    	$(INSTALL_DIR) $(1)/bin/
    	$(INSTALL_BIN) $(PKG_BUILD_DIR)/helloWorld $(1)/bin/helloWorld
    $(eval $(call BuildPackage,helloWorld)) 

    Of course alot of that lines are from openwrt hello world tutorials or from onion omega projects. I also remove some lines, so if it not compile its because I erased to much šŸ™‚ ... I tried to keep it clean here... sry.

    PS: thanks alot for your help!

    PSS: I found this statistic: http://www.etalabs.net/compare_libcs.html
    Is it possible that compiling the os with musl is faster and smaller then with uClibc?

  • Hi Alexander,

    Below are in a few steps my way to success in building my cross platform apps:

    1. I run a CentOS 6.5 linux box (32bit)

    2. download the 32bits mips toolchain for Onion to /usr from this link https://s3-us-west-2.amazonaws.com/onion-downloads/openwrt/OpenWrt-Toolchain-ar71xx-generic_gcc-4.8-linaro_uClibc-

    3. unpack this toolchain using:
      cd /usr
      tar -xvf OpenWrt-Toolchain-ar71xx-generic_gcc-4.8-linaro_uClibc-

    4. move the extracted dir to a shorter name:
      mv OpenWrt-Toolchain-ar71xx-generic_gcc-4.8-linaro_uClibc- onion

    5. in your app directory create Makefile.onion with following contents:

    CC = /usr/onion/toolchain-mips_34kc_gcc-4.8-linaro_uClibc-
    LD = /usr/onion/toolchain-mips_34kc_gcc-4.8-linaro_uClibc-
    CFLAGS = -I /usr/onion/toolchain-mips_34kc_gcc-4.8-linaro_uClibc-
    LDFLAGS = -L /usr/onion/toolchain-mips_34kc_gcc-4.8-linaro_uClibc-

    EXEC= hello.onion

    THREADLIB = -lpthread
    RTLIB = -lrt
    DLLIB = -ldl

    IFLAGS = -I..

    all: clean $(EXEC)


    $(EXEC): $(OBJS)
    $(CC) -o $(EXEC) $(OBJS) $(LDFLAGS)

    rm -rf $(OBJS) $(EXEC)

    $(CC) -c -o $@ $(DEBUG) $(CFLAGS) $(IFLAGS) $<

    $(CC) -c $(CFLAGS) $(DEBUG) $< -o $@ $(IFLAGS)

    hello.o: ../hello.cpp
    6) make your hello app: make -f Makefile.onion

    1. copy hello.onion to Onion and give it exec rights

  • Thank you for your suggestion,

    I know that a lot of people just use the SDK to compile programs, but I want to get the openWRT package CrossCompile environment to work. I want to create packages that I can install on the onion (.ipk packages if I'm remember correctly). I don't know how to get the toolchain you suggested into the openWRT environment, so if you have an Idea how to do that, it would be perfect ā¤

    I mean someone šŸ˜‰ compiles their packages with the correct toolchain/setup and provide this packages to us, don't they?

  • Hi @Alexander-Pitzer, In the make menuconfig system, go into Advanced configuration options (for developers) > Toolchain Options > C Library implementation. You just need to switch from musl to uClibc.

  • @Boken-Lin


    Yeah I tried this before, too. But there is no option for uClibc....
    May it be possible to poste a .conf with the right kernel settings?

    Because the dependency for uClibc contains : .... && !mips [=y] && ....
    and mips is set by: .... || TARGET_ar71xx_generic [=y] && <choice> && TARGET_ar71xx [=y] || ....


  • @Alexander-Pitzer that's quite strange. Where did you get the buildroot files?

  • @Boken-Lin


    I believe I found the problem, in the current version of openWRT uClibc is available if broken packages are allowed. RIght now I compile the toolchain: toolchain-mips_34kc_gcc-5.2.0_uClibc-1.0.9
    They switched to uClibc-ng-1.0.9

    8e493a4b7c0749bf65cfd545ca18b384bc1d4f32    12/03/2015 03:47 PM
    uClibc-ng: update to 1.0.9
    Update to 1.0.9, switch to XZ tarball.
    Signed-off-by: Waldemar Brodkorb <wbx@uclibc-ng.org>
    git-svn-id: svn://svn.openwrt.org/openwrt/trunk@47715 3c298f89-4303-0410-b956-a3cf2f4a3e73
    b70a36d1d969f5aa9ad081c9a395633793582a5a  11/02/2015 07:12 PM
    uclibc: remove version 0.9.33
    Latest uClibc-ng is now the only supported option
    Signed-off-by: Felix Fietkau <nbd@openwrt.org>
    git-svn-id: svn://svn.openwrt.org/openwrt/trunk@47357 3c298f89-4303-0410-b956-a3cf2f4a3e73

  • @Alexander-Pitzer Oh i see. Were you using a version of the buildroot that did not include uClibc?

  • Sry I updated my post... so yes uClibc was kicked and uClibc-ng is in but only as broken package

  • @Alexander-Pitzer Bummer. I guess the only way to do it right now is to check out f14d574f3082577a4489f778d0c8cf7117d33cee commit, and come back to the new one once the broken package has been fixed...

  • @Boken-Lin I try to compile the new version and will play around with the toolchain a bit. If nothing helps I will go back. Thank's alot for your help. The Onion Omega is a great product and I really like to play around with it alot!

  • @Alexander-Pitzer I'm glad you like it šŸ™‚ If there's anything else we can help you with just let us know!

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