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110 lines
4.2 KiB
Text
110 lines
4.2 KiB
Text
Compilation and pre-built binaries FAQ
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======================================
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What is the best pre-built binary for my system or device?
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----------------------------------------------------------
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None. The best binary is compiled by yourself using a toolchain that is
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optimized for your system or device in every respect.
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How do I compile my own binary?
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-------------------------------
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On a full blown desktop system this is relativly easy. If not already done so,
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install a C compiler (e.g. gcc or clang) through your packet manager, e.g.
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"sudo apt-get install gcc" (Debian/Ubuntu) or "sudo yum install gcc"
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(RedHat/Fedora).
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Then cd to your vlmcsd directory and type "make". vlmcs and vlmcsd will
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be built right away for your local system.
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If you installed gcc and it is not the default compiler for your OS or
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distribution, you may need to type "make CC=gcc" to explicitly select a
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specific C compiller.
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How do I compile a binary for my embedded device?
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-------------------------------------------------
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What you need is cross-compiling toolchain for your device. It consists of a
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C compiler, libraries, header files and some tools (called binutils). The
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toolchain must match the device in processor architecture, endianess, ABI,
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library and header files version, library configuration, ...
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If the endianess or ABI differs or the version of some library between
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toolchain and device differs too much, the resulting binary does not run
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on your device.
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Once you have a proper toolchain (probably found on the Internet for download),
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unpack it to any directory and type
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"make CC=/path/to/toolchain/bindir/c-compiler-binary"
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Building vlmcsd for using a cross-compiling toolchain is as easy as building
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vlmcsd for your local machine. The only question is, whether this you have
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a toolchain that actually matches your device.
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Whenever you change any parameter of the make command line, you must "clean"
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the source directory from intermediate files and output from previous runs
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of make. You can do so by typeing "make clean" or force make to behave as if
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the directory were clean by adding -B to the command line, e.g.
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"make -B CC=/path/to/toolchain/bindir/c-compiler-binary"
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I have downloaded several promising toolchains for my device but they all
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don't work. Can I create my own toolchain?
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-------------------------------------------------------------------------
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You can use tools like buildroot or OpenWRT. Both are able to create toolchains
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for many embedded devices. But this is out of the scope of this document.
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If you are unable to walk through thousands of configuration options and make
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the right choice, you may probably want to try the pre-built binaries.
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How to choose a pre-built binary?
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---------------------------------
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The directory structure for the binaries is
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binaries
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+
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+--<operating system>
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+
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+--<cpu arch>
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+
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+--<endianess> (omitted if CPU or OS does not allow multi-endianess)
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+
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+--<C-library>
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<C-library> can also be "static". That means no special library is required.
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Static binaries are much bigger and need more RAM than dynamic binaries but
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are more likely to run on your system. Use a static binary only, if none of
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the dynmic binaries run.
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Don't get confused when a binary is named after an OS or a specific device,
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e.g. the name contains "openwrt", "tomato" or "Fritzbox". This does not mean
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that the binary will run only on that OS or on that device. It is a hint only
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where I got or built the toolchain from.
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How to determine the endianess of my system?
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--------------------------------------------
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- All Intel CPUs (x86, x32, x64) are little-endian only
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- Windows is little-endian only even if the CPU support big-endian
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- big-endian ARM is extremely uncommon. You can safely assume little-endian
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- little-endian PowerPC virtually does not exist since only newer POWER7
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and POWER8 CPUs support it. Always assume big-endian.
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- For MIPS both little-endian and big-endian are common. Most Broadcomm and
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TI chips run little-endian. Most Atheros and Ikanos CPUs run big-endian.
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Try typing
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echo -n I | od -o | awk 'FNR==1{ print substr($2,6,1)}'
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This returns 1 for little-endian systems and 0 for big-endian systems. However
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some devices do not have the od command and thus this method won't work.
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