From f628d68dab3914c68de60985c2cd0b089fb68af3 Mon Sep 17 00:00:00 2001 From: Rob Landley Date: Sun, 22 May 2022 19:35:51 -0500 Subject: [PATCH] More on cross compiling. --- www/faq.html | 86 +++++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 71 insertions(+), 15 deletions(-) diff --git a/www/faq.html b/www/faq.html index e6fa6160..fa2d2cd7 100755 --- a/www/faq.html +++ b/www/faq.html @@ -26,6 +26,7 @@

  • How do I install toybox?

  • How do I cross compile toybox?

    • +

  • What architectures does toybox support?

  • What part of Linux/Android does toybox provide?

  • How do I build a working Linux system with toybox?

    • @@ -71,7 +72,7 @@ implementing a new SMB server from scratch to replace samba, switching bash with zsh, and so on. -Toybox itself exists because somebody with in a legacy position +Toybox itself exists because somebody in a legacy position just wouldn't shut up about GPLv3, otherwise I would probably still happily be maintaining BusyBox. (For more on how I wound up working on busybox in the first place, @@ -351,8 +352,7 @@ but develops on a standard 64-bit Linux+glibc distro while building embedded and is not a Google employee so does not have access to the Google build cluster of powerful machines capable of running the full AOSP build in a reasonable amount of time. Rob is working to get android -building under android (the list of -toybox tools Android's build uses is +building under android (the list of toybox tools Android's build uses is here, and what else it needs from its build environment is here), and he hopes someday to not only make a usable development @@ -525,10 +525,59 @@ run on your target. A toolchain is an integrated suite of compiler, assembler, and linker, plus the standard headers and libraries necessary to build C programs. (And a few miscellaneous binaries like -nm and objdump.)

    +nm and objdump that display info about ELF files.)

    -

    Toybox is tested against two compilers (llvm, gcc) and three C libraries -(bionic, musl, glibc) in the following combinations:

    +

    Toybox supports the standard $CROSS_COMPILE prefix environnment variable, +same as the Linux kernel build uses. This is used to prefix all the tools +(target-cc, target-ld, target-strip) during the build, meaning the prefix +usually ends with a "-" that's easy to forget but kind of important +("target-cc" and "targetcc" are not the same name).

    + +

    You can either provide a +full path in the CROSS_COMPILE string, or add the appropriate bin directory +to your $PATH. I.E:

    + +
    +

    make LDFLAGS=--static CROSS_COMPILE=~/musl-cross-make/ccc/m68k-linux-musl-cross/bin/m68k-linux-musl- distclean defconfig toybox

     +
    + +

    Is equivalent to:

    + +

    +export "PATH=~/musl-cross-make/ccc/m68k-linux-musl-cross/bin:$PATH"
    +LDFLAGS=--static CROSS_COMPILE=m68k-linux-musl- make distclean defconfig toybox +

    + +

    (Both of those examples use static linking so you can install just +the single file to target, or test them with "qemu-m68k toybox". Feel free +to dynamically link instead if you prefer, mkroot offers a "dynamic" +add-on to copy the compiler's shared libraries into the new root +filesystem.)

    + +

    Toybox's system builder can use a simpler $CROSS +variable to specify the target(s) to build for if you've installed +compatible cross compilers under the "ccc" directory. +Behind the scenes this uses wildcard expansion to set $CROSS_COMPILER to +an appropriate path/prefix-.

    + +

    Q: What architectures does toybox support?

    + +

    Toybox runs on 64 bit and 32 bit processors, little endian and big endian, +tries to respect alignment, and will enable nommu support when fork() is +unavailable (or when TOYBOX_FORCE_NOMMU is enabled in the config to +work around broken nommu toolchains), but otherwise tries to be +processor agnostic (although some commands such as strace can't avoid +a processor-specific if/else staircase.).

    + +

    Several commands (such as ps/top) are unavoidably full of Linux assumptions. +Some subset of the commands have been made to run on BSD and MacOS X, and +lib/portability.* and scripts/genconfig.sh exist to catch some known +variations.

    +

    + +

    Each release gets tested against two compilers (llvm, gcc), three C +libraries (bionic, musl, glibc), and a half-dozen different processor +types, in the following combinations:

    1) gcc+glibc = host toolchain

    @@ -554,15 +603,15 @@ installed on the system alongside the static binary: These days glibc is maintained by a committee instead of a single maintainer, if that's an improvement. (As with Windows and -Cobol, most people deal with it and get on with their lives.)

    +Cobol, most people just try to get on with their lives.)

    2) gcc+musl = musl-cross-make

    -

    The cross compilers I test this with are built from the +

    These cross compilers are built from the musl-libc maintainer's musl-cross-make -project, built by running toybox's scripts/mcm-buildall.sh in that directory, +project, built by running toybox's scripts/mcm-buildall.sh in that directory, and then symlink the resulting "ccc" subdirectory into toybox where "make root CROSS=" can find them, ala:

    @@ -575,7 +624,14 @@ cd musl-cross-make ln -s $(realpath ccc) ../toybox/ccc -

    Instead of symlinking ccc, you can specify a CROSS_COMPILE= prefix +

    Since this takes a long time to run, and builds lots of targets +(cross and native), we've uploaded +the resulting binaries +so you can wget and extract a tarball or two instead of +compiling them all yourself. (See the README in that directory for details. +Yes there's a big source tarball in there for license compliance reasons.)

    + +

    Instead of CROSS= you can also specify a CROSS_COMPILE= prefix in the same format the Linux kernel build uses. You can either provide a full path in the CROSS_COMPILE string, or add the appropriate bin directory to your $PATH. I.E:

    @@ -591,14 +647,14 @@ export "PATH=~/musl-cross-make/ccc/m68k-linux-musl-cross/bin:$PATH"
    LDFLAGS=--static make distclean defconfig toybox CROSS=m68k-linux-musl-

    -

    Note: these examples use static linking becausae a dynamic musl binary +

    Note: these examples use static linking because a dynamic musl binary won't run on your host unless you install musl's libc.so into the system libraries (which is an accident waiting to happen adding a second C library to most glibc linux distribution) or play with $LD_LIBRARY_PATH. -In theory you could "make root" a dynamic root filesystem with musl by copying -the shared libraries out of the toolchain, but I haven't bothered implementing -that in mkroot yet because a static linked musl hello world is 10k on x86 -(5k if stripped).

    +(The dynamic package +in mkroot copies the shared libraries out of the toolchain to create a dynamic +linking environment in the root filesystem, but it's not nearly as well +tested.)

    3) llvm+bionic = Android NDK