How to build busybox statically against uclibc, minimizing its size. Very sketchy at the moment. Send questions to vda.linux@googlemail.com. First, build and install cross-compiling toolchain. Start with binutils. When binutils are built and installed, you should have these files: $ ls -l /usr/bin/i486-linux-uclibc-* | grep binutils lrwxrwxrwx 1 root root 72 Jul 21 18:17 /usr/bin/i486-linux-uclibc-addr2line -> /usr/app/binutils-2.17-i486-linux-uclibc/bin/i486-linux-uclibc-addr2line lrwxrwxrwx 1 root root 65 Jul 21 18:17 /usr/bin/i486-linux-uclibc-ar -> /usr/app/binutils-2.17-i486-linux-uclibc/bin/i486-linux-uclibc-ar lrwxrwxrwx 1 root root 65 Jul 21 18:17 /usr/bin/i486-linux-uclibc-as -> /usr/app/binutils-2.17-i486-linux-uclibc/bin/i486-linux-uclibc-as lrwxrwxrwx 1 root root 70 Jul 21 18:17 /usr/bin/i486-linux-uclibc-c++filt -> /usr/app/binutils-2.17-i486-linux-uclibc/bin/i486-linux-uclibc-c++filt lrwxrwxrwx 1 root root 65 Jul 21 18:17 /usr/bin/i486-linux-uclibc-ld -> /usr/app/binutils-2.17-i486-linux-uclibc/bin/i486-linux-uclibc-ld lrwxrwxrwx 1 root root 65 Jul 21 18:17 /usr/bin/i486-linux-uclibc-nm -> /usr/app/binutils-2.17-i486-linux-uclibc/bin/i486-linux-uclibc-nm lrwxrwxrwx 1 root root 70 Jul 21 18:17 /usr/bin/i486-linux-uclibc-objcopy -> /usr/app/binutils-2.17-i486-linux-uclibc/bin/i486-linux-uclibc-objcopy lrwxrwxrwx 1 root root 70 Jul 21 18:17 /usr/bin/i486-linux-uclibc-objdump -> /usr/app/binutils-2.17-i486-linux-uclibc/bin/i486-linux-uclibc-objdump lrwxrwxrwx 1 root root 69 Jul 21 18:17 /usr/bin/i486-linux-uclibc-ranlib -> /usr/app/binutils-2.17-i486-linux-uclibc/bin/i486-linux-uclibc-ranlib lrwxrwxrwx 1 root root 70 Jul 21 18:17 /usr/bin/i486-linux-uclibc-readelf -> /usr/app/binutils-2.17-i486-linux-uclibc/bin/i486-linux-uclibc-readelf lrwxrwxrwx 1 root root 67 Jul 21 18:17 /usr/bin/i486-linux-uclibc-size -> /usr/app/binutils-2.17-i486-linux-uclibc/bin/i486-linux-uclibc-size lrwxrwxrwx 1 root root 70 Jul 21 18:17 /usr/bin/i486-linux-uclibc-strings -> /usr/app/binutils-2.17-i486-linux-uclibc/bin/i486-linux-uclibc-strings lrwxrwxrwx 1 root root 68 Jul 21 18:17 /usr/bin/i486-linux-uclibc-strip -> /usr/app/binutils-2.17-i486-linux-uclibc/bin/i486-linux-uclibc-strip After that, build cross-gcc. You should now have this: $ ls -l /usr/bin/i486-linux-uclibc-* | grep -v binutils lrwxrwxrwx 1 root root 62 Aug 21 13:38 /usr/bin/i486-linux-uclibc-c++ -> /usr/app/gcc-4.2.1-i486-linux-uclibc/bin/i486-linux-uclibc-c++ lrwxrwxrwx 1 root root 62 Aug 21 13:38 /usr/bin/i486-linux-uclibc-cpp -> /usr/app/gcc-4.2.1-i486-linux-uclibc/bin/i486-linux-uclibc-cpp lrwxrwxrwx 1 root root 62 Aug 21 13:38 /usr/bin/i486-linux-uclibc-g++ -> /usr/app/gcc-4.2.1-i486-linux-uclibc/bin/i486-linux-uclibc-g++ lrwxrwxrwx 1 root root 62 Aug 21 13:38 /usr/bin/i486-linux-uclibc-gcc -> /usr/app/gcc-4.2.1-i486-linux-uclibc/bin/i486-linux-uclibc-gcc lrwxrwxrwx 1 root root 68 Aug 21 12:43 /usr/bin/i486-linux-uclibc-gcc-4.1.1 -> /usr/app/gcc-4.1.1-i486-linux-uclibc/bin/i486-linux-uclibc-gcc-4.1.1 lrwxrwxrwx 1 root root 68 Aug 21 13:38 /usr/bin/i486-linux-uclibc-gcc-4.2.1 -> /usr/app/gcc-4.2.1-i486-linux-uclibc/bin/i486-linux-uclibc-gcc-4.2.1 lrwxrwxrwx 1 root root 65 Aug 21 13:38 /usr/bin/i486-linux-uclibc-gccbug -> /usr/app/gcc-4.2.1-i486-linux-uclibc/bin/i486-linux-uclibc-gccbug lrwxrwxrwx 1 root root 63 Aug 21 13:38 /usr/bin/i486-linux-uclibc-gcov -> /usr/app/gcc-4.2.1-i486-linux-uclibc/bin/i486-linux-uclibc-gcov Depending on your packaging choice, you may end up with actual files in /usr/bin, not symlinks. In fact, having symlinks is not typical, but I find it much more convenient. Now you need to build uclibc. Full uclibc .config can be found at the end of this file. Key points: Uncheck shared library support: [ ] Generate only Position Independent Code (PIC) [ ] Enable support for shared libraries Since busybox uses --gc-sections, it's advantageous to pass "-ffunction-sections -fdata-sections" options to gcc. This will make your busybox binary ~6k smaller. I set the following option in .config for that: UCLIBC_EXTRA_CFLAGS="-ffunction-sections -fdata-sections -falign-functions=1 -falign-labels=1 -falign-loops=1 -falign-jumps=1 -fomit-frame-pointer" Build and install you uclibc. Now you can build busybox against it by using export ARCH=i386 make CROSS_COMPILE=i486-linux-uclibc- ... After you built it, find busybox_ld.out file in the top build directory, rename it to busybox_ldscript, remove everything except linker script, and edit it as follows: --- busybox_ld.out 2007-09-16 20:19:51.000000000 +0100 +++ busybox_ldscript 2007-08-25 18:10:15.000000000 +0100 @@ -65,7 +65,7 @@ PROVIDE (__etext = .); PROVIDE (_etext = .); PROVIDE (etext = .); - .rodata : { *(.rodata .rodata.* .gnu.linkonce.r.*) } + .rodata : { *(.rodata SORT_BY_ALIGNMENT(.rodata.*) .gnu.linkonce.r.*) } .rodata1 : { *(.rodata1) } .eh_frame_hdr : { *(.eh_frame_hdr) } .eh_frame : ONLY_IF_RO { KEEP (*(.eh_frame)) } @@ -134,7 +134,7 @@ .got.plt : { *(.got.plt) } .data : { - *(.data .data.* .gnu.linkonce.d.*) + *(.data SORT_BY_ALIGNMENT(.data.*) .gnu.linkonce.d.*) KEEP (*(.gnu.linkonce.d.*personality*)) SORT(CONSTRUCTORS) } @@ -144,7 +144,7 @@ .bss : { *(.dynbss) - *(.bss .bss.* .gnu.linkonce.b.*) + *(.bss SORT_BY_ALIGNMENT(.bss.*) .gnu.linkonce.b.*) *(COMMON) /* Align here to ensure that the .bss section occupies space up to _end. Align after .bss to ensure correct alignment even if the Now delete busybox and busybox_unstripped binaries, and rerun make. It will do final link again, with smaller result. Example: $ size busybox busybox.optimized text data bss dec hex filename 772898 1084 10844 784826 bf9ba busybox 772680 1051 10724 784455 bf847 busybox.optimized Nearly 400 bytes saved on padding. Sample uclibc .config follows ============================= # # Automatically generated make config: don't edit # Fri Aug 3 12:16:10 2007 # # TARGET_alpha is not set # TARGET_arm is not set # TARGET_bfin is not set # TARGET_cris is not set # TARGET_e1 is not set # TARGET_frv is not set # TARGET_h8300 is not set # TARGET_hppa is not set TARGET_i386=y # TARGET_i960 is not set # TARGET_ia64 is not set # TARGET_m68k is not set # TARGET_microblaze is not set # TARGET_mips is not set # TARGET_nios is not set # TARGET_nios2 is not set # TARGET_powerpc is not set # TARGET_sh is not set # TARGET_sh64 is not set # TARGET_sparc is not set # TARGET_v850 is not set # TARGET_vax is not set # TARGET_x86_64 is not set # # Target Architecture Features and Options # TARGET_ARCH="i386" FORCE_OPTIONS_FOR_ARCH=y # CONFIG_GENERIC_386 is not set # CONFIG_386 is not set CONFIG_486=y # CONFIG_586 is not set # CONFIG_586MMX is not set # CONFIG_686 is not set # CONFIG_PENTIUMII is not set # CONFIG_PENTIUMIII is not set # CONFIG_PENTIUM4 is not set # CONFIG_K6 is not set # CONFIG_K7 is not set # CONFIG_ELAN is not set # CONFIG_CRUSOE is not set # CONFIG_WINCHIPC6 is not set # CONFIG_WINCHIP2 is not set # CONFIG_CYRIXIII is not set # CONFIG_NEHEMIAH is not set TARGET_SUBARCH="" # # Using ELF file format # ARCH_LITTLE_ENDIAN=y # # Using Little Endian # ARCH_HAS_MMU=y ARCH_USE_MMU=y UCLIBC_HAS_FLOATS=y UCLIBC_HAS_FPU=y DO_C99_MATH=y KERNEL_HEADERS="../linux-2.6.18.1/include" HAVE_DOT_CONFIG=y # # General Library Settings # # HAVE_NO_PIC is not set # DOPIC is not set # HAVE_NO_SHARED is not set # ARCH_HAS_NO_LDSO is not set # HAVE_SHARED is not set UCLIBC_CTOR_DTOR=y # HAS_NO_THREADS is not set # UCLIBC_HAS_THREADS is not set UCLIBC_HAS_LFS=y # MALLOC is not set # MALLOC_SIMPLE is not set MALLOC_STANDARD=y # MALLOC_GLIBC_COMPAT is not set UCLIBC_DYNAMIC_ATEXIT=y # COMPAT_ATEXIT is not set # UCLIBC_SUSV3_LEGACY is not set # UCLIBC_SUSV3_LEGACY_MACROS is not set UCLIBC_HAS_SHADOW=y # UCLIBC_HAS_PROGRAM_INVOCATION_NAME is not set UCLIBC_HAS___PROGNAME=y UNIX98PTY_ONLY=y ASSUME_DEVPTS=y UCLIBC_HAS_TM_EXTENSIONS=y UCLIBC_HAS_TZ_CACHING=y UCLIBC_HAS_TZ_FILE=y UCLIBC_HAS_TZ_FILE_READ_MANY=y UCLIBC_TZ_FILE_PATH="/etc/TZ" # # Advanced Library Settings # UCLIBC_PWD_BUFFER_SIZE=256 UCLIBC_GRP_BUFFER_SIZE=256 # # Networking Support # UCLIBC_HAS_IPV6=y UCLIBC_HAS_RPC=y UCLIBC_HAS_FULL_RPC=y UCLIBC_HAS_REENTRANT_RPC=y # UCLIBC_USE_NETLINK is not set # UCLIBC_HAS_BSD_RES_CLOSE is not set # # String and Stdio Support # UCLIBC_HAS_STRING_GENERIC_OPT=y UCLIBC_HAS_STRING_ARCH_OPT=y UCLIBC_HAS_CTYPE_TABLES=y UCLIBC_HAS_CTYPE_SIGNED=y UCLIBC_HAS_CTYPE_UNSAFE=y # UCLIBC_HAS_CTYPE_CHECKED is not set # UCLIBC_HAS_CTYPE_ENFORCED is not set # UCLIBC_HAS_WCHAR is not set # UCLIBC_HAS_LOCALE is not set # UCLIBC_HAS_HEXADECIMAL_FLOATS is not set # UCLIBC_HAS_GLIBC_CUSTOM_PRINTF is not set # USE_OLD_VFPRINTF is not set UCLIBC_PRINTF_SCANF_POSITIONAL_ARGS=9 # UCLIBC_HAS_SCANF_GLIBC_A_FLAG is not set # UCLIBC_HAS_STDIO_BUFSIZ_NONE is not set # UCLIBC_HAS_STDIO_BUFSIZ_256 is not set # UCLIBC_HAS_STDIO_BUFSIZ_512 is not set UCLIBC_HAS_STDIO_BUFSIZ_1024=y # UCLIBC_HAS_STDIO_BUFSIZ_2048 is not set # UCLIBC_HAS_STDIO_BUFSIZ_4096 is not set # UCLIBC_HAS_STDIO_BUFSIZ_8192 is not set UCLIBC_HAS_STDIO_BUILTIN_BUFFER_NONE=y # UCLIBC_HAS_STDIO_BUILTIN_BUFFER_4 is not set # UCLIBC_HAS_STDIO_BUILTIN_BUFFER_8 is not set # UCLIBC_HAS_STDIO_SHUTDOWN_ON_ABORT is not set UCLIBC_HAS_STDIO_GETC_MACRO=y UCLIBC_HAS_STDIO_PUTC_MACRO=y UCLIBC_HAS_STDIO_AUTO_RW_TRANSITION=y # UCLIBC_HAS_FOPEN_LARGEFILE_MODE is not set # UCLIBC_HAS_FOPEN_EXCLUSIVE_MODE is not set # UCLIBC_HAS_GLIBC_CUSTOM_STREAMS is not set UCLIBC_HAS_PRINTF_M_SPEC=y UCLIBC_HAS_ERRNO_MESSAGES=y # UCLIBC_HAS_SYS_ERRLIST is not set UCLIBC_HAS_SIGNUM_MESSAGES=y # UCLIBC_HAS_SYS_SIGLIST is not set UCLIBC_HAS_GNU_GETOPT=y UCLIBC_HAS_GNU_GETSUBOPT=y # # Big and Tall # UCLIBC_HAS_REGEX=y UCLIBC_HAS_REGEX_OLD=y UCLIBC_HAS_FNMATCH=y UCLIBC_HAS_FNMATCH_OLD=y UCLIBC_HAS_WORDEXP=y UCLIBC_HAS_FTW=y UCLIBC_HAS_GLOB=y # UCLIBC_HAS_GNU_GLOB is not set # # Library Installation Options # RUNTIME_PREFIX="/usr/app/uclibc-NEW/$(TARGET_ARCH)/" DEVEL_PREFIX="/usr/app/uclibc-NEW/$(TARGET_ARCH)/usr/" # # Security options # # UCLIBC_HAS_ARC4RANDOM is not set # HAVE_NO_SSP is not set # UCLIBC_HAS_SSP is not set UCLIBC_BUILD_NOEXECSTACK=y # # uClibc development/debugging options # CROSS_COMPILER_PREFIX="" UCLIBC_EXTRA_CFLAGS="-ffunction-sections -fdata-sections -falign-functions=1 -falign-labels=1 -falign-loops=1 -falign-jumps=1 -fomit-frame-pointer" # DODEBUG is not set DOSTRIP=y # DOASSERTS is not set # UCLIBC_MALLOC_DEBUGGING is not set WARNINGS="-Wall" # EXTRA_WARNINGS is not set # DOMULTI is not set # UCLIBC_MJN3_ONLY is not set