Difference between revisions of "Compiling on OpenWRT"

Compiling on OpenWRT (view source)

Revision as of 18:18, 19 October 2020

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**Additional utilities are recommended
**Additional utilities are recommended
***Install the full version of BASH: opkg install bash
***Install the full version of BASH: opkg install bash
*Environment variables to add;
*Environment Variables to add (these can be added in a myriad of ways, see the end of this section;
**export LDFLAGS="-Wl,-rpath=/usr/lib:/opt/lib -Wl,--dynamic-linker=/opt/lib/ld-linux.so.3 -L/opt/lib (the DD-WRT / Entware version: export LDFLAGS="-Wl,-rpath=/opt/lib -Wl,--dynamic-linker=/opt/lib/ld-linux.so.3 -L/opt/lib", needs to be modified for OpenWRT)
**export LDFLAGS="-Wl,-rpath=/usr/lib:/opt/lib -Wl,--dynamic-linker=/usr/lib/gcc/arm-openwrt-linux-muslgnueabi/7.4.0/ld-musl-armhf.so.1 -L/usr/lib:/opt/lib:/opt/include
**NOTE: The original DD-WRT / Entware version is this: export LDFLAGS="-Wl,-rpath=/opt/lib -Wl,--dynamic-linker=/opt/lib/ld-linux.so.3 -L/opt/lib", and needs to be modified for OpenWRT as shown above.
***-WI is a switch that allows for additional items to be added via the GNU [https://ftp.gnu.org/old-gnu/Manuals/ld-2.9.1/html_node/ld_3.html LD] (https://stackoverflow.com/questions/6562403/i-dont-understand-wl-rpath-wl) command
***-WI is a switch that allows for additional items to be added via the GNU [https://ftp.gnu.org/old-gnu/Manuals/ld-2.9.1/html_node/ld_3.html LD] (https://stackoverflow.com/questions/6562403/i-dont-understand-wl-rpath-wl) command
***-rpath in LDLFLAGS = "-rpath=/usr/lib:/opt/lib" is the same as executing this on the command line: export LD_LIBRARY_PATH = "/opt/lib
***-rpath in LDLFLAGS = "-rpath=/usr/lib:/opt/lib" is the same as executing this on the command line: export LD_LIBRARY_PATH = "/opt/lib
****rpath AND/OR <code>LD_LIBRARY_PATH</code> is a path used by an executable program to search directories containing shared libraries after the program has been compiled (from https://en.wikipedia.org/wiki/Rpath and https://stackoverflow.com/questions/4250624/ld-library-path-vs-library-path)
****rpath AND/OR <code>LD_LIBRARY_PATH</code> is a path used by an executable program to search directories containing shared libraries after the program has been compiled (from https://en.wikipedia.org/wiki/Rpath and https://stackoverflow.com/questions/4250624/ld-library-path-vs-library-path)
****OpenWRT has its own equivalent path, which is /usr/lib, however there are some variations in files and sizes.  Solution?  Include both paths;
****OpenWRT has its own equivalent path, which is /usr/lib, however there are some variations in files and sizes.  Solution?  Include both paths (from https://www.linuxtopia.org/online_books/an_introduction_to_gcc/gccintro_24.html);
*****-rpath=/usr/lib:/opt/lib (this will search OpenWRT's /usr/lib directory first, then DD-WRT / Entware's /opt/lib directory second)
*****-rpath=/usr/lib:/opt/lib (this will search OpenWRT's /usr/lib directory first, then DD-WRT / Entware's /opt/lib directory second)
***--dynamic-linker
***--dynamic-linker
****For DD-WRT / Entware it is located here: /opt/lib/ld-linux.so.3, which is a symbolic link to ld-2.27.so (and here too: /lib/gcc/arm-openwrt-linux-gnueabi/7.4.0)
****For DD-WRT / Entware, the GNU LD file is located here: /opt/lib/ld-linux.so.3, which is a symbolic link to ld-2.27.so (and here too: /lib/gcc/arm-openwrt-linux-gnueabi/7.4.0)
****OpenWRT seems to have an equivalent GNU LD file located here: usr/lib/gcc/arm-openwrt-linux-muslgnueabi/7.4.0/ld-musl-armhf.so.1, but tragically, there is no environment path set.
****OpenWRT seems to have an equivalent GNU LD file located here: /usr/lib/gcc/arm-openwrt-linux-muslgnueabi/7.4.0/ld-musl-armhf.so.1, so use that path instead
****Note: LD is not the same as GNU LD (https://en.wikipedia.org/wiki/Linker_(computing)#GNU_linker<nowiki/>)
*****--dynamic-linker /usr/lib/gcc/arm-openwrt-linux-muslgnueabi/7.4.0/ld-musl-armhf.so.1
***ELF Definition: https://en.wikipedia.org/wiki/Executable_and_Linkable_Format
****LD is not the same as GNU LD (https://en.wikipedia.org/wiki/Linker_(computing)#GNU_linker<nowiki/>)
***-L in LDLFLAGS = "-L/opt/lib" is the same as: export LIBRARY_PATH=/opt/lib (https://gcc.gnu.org/onlinedocs/gcc/Environment-Variables.html)
***<nowiki/>-L in LDLFLAGS = "-L/usr/lib:/opt/lib:/opt/include" is the same as executing this on the command line: export LIBRARY_PATH=/usr/lib:/opt/lib:/opt/include (https://gcc.gnu.org/onlinedocs/gcc/Environment-Variables.html)
****<code>LIBRARY_PATH</code> is used by gcc before compilation to search directories containing static and shared libraries that need to be linked to your program (from https://stackoverflow.com/questions/4250624/ld-library-path-vs-library-path)
****<code>LIBRARY_PATH</code> is used by gcc before compilation to search directories containing static and shared libraries that need to be linked to your program (from https://stackoverflow.com/questions/4250624/ld-library-path-vs-library-path)
****
*****
*****
**export CFLAGS="-O2 -pipe -march=armv7-a -mtune=cortex-a9 -fno-caller-saves -mfloat-abi=soft ", but...
**export CFLAGS="-O2 -pipe -march=armv7-a -mtune=cortex-a9 -fno-caller-saves -mfloat-abi=soft -I/opt/include "
***...but because this is OpenWRT, not DD-WRT, add an item to the end of it: export CFLAGS="-O2 -pipe -march=armv7-a -mtune=cortex-a9 -fno-caller-saves -mfloat-abi=soft -I/opt/include"
**NOTE: The original DD-WRT / Entware version is this: export CFLAGS="-O2 -pipe -march=armv7-a -mtune=cortex-a9 -fno-caller-saves -mfloat-abi=soft ", and needs to be modified for OpenWRT as shown above.
***CFLAGS = "-I/opt/include" is the same as: export CPATH=/opt/include (https://gcc.gnu.org/onlinedocs/cpp/Environment-Variables.html
***-I in CFLAGS = "-I/opt/include" is the same as: export CPATH=/opt/include (from https://gcc.gnu.org/onlinedocs/cpp/Environment-Variables.html)
***NOTE: that's an "I" (eye) in the above command, as in the word "Inside, Inner, Implode, etc., not a "l" (el), as in the word Little, Lime, etc.
**Adding the above Environment Variables;
***Run each of the below command lines
****export LDFLAGS="-Wl,-rpath=/usr/lib:/opt/lib -Wl,--dynamic-linker=/usr/lib/gcc/arm-openwrt-linux-muslgnueabi/7.4.0/ld-musl-armhf.so.1 -L/usr/lib:/opt/lib:/opt/include
****export CFLAGS="-O2 -pipe -march=armv7-a -mtune=cortex-a9 -fno-caller-saves -mfloat-abi=soft  -I/opt/include "
***Put the above two EXPORT commands in a single file, and run the following command;
****source WhatEverFileName
***Add the above two EXPORT commands to a user's profile
****nano ~/.profile
****NOTE: For the above to work, the full BASH shell must be installed (opkg install bash) AND the ~/.profile file must include the directive: SHELL=/bin/bash
*...as far as the Entware documentation for Compiling: https://github.com/Entware/Entware/wiki/Using-GCC-for-native-compilation
*...as far as the Entware documentation for Compiling: https://github.com/Entware/Entware/wiki/Using-GCC-for-native-compilation
**Additional information for the ./configure --prefix /opt command, and what --prefix means: https://askubuntu.com/questions/891835/what-does-prefix-do-exactly-when-used-in-configure
**Additional information for the ./configure --prefix /opt command, and what --prefix means: https://askubuntu.com/questions/891835/what-does-prefix-do-exactly-when-used-in-configure
**Although they offer a link and a command for downloading additional libraries to /opt/include, there doesn't appear to be any notation of where that is utilized.  Just having it as a bunch of files in a directory is useless unless a compiler like GCC can make use of the files.  It should be
**Although they offer a link and a command for downloading additional libraries to /opt/include, there doesn't appear to be any notation of where that is utilized.  Just having it as a bunch of files in a directory is useless unless a compiler like GCC can make use of the files.  It should be
*ELF Definition: https://en.wikipedia.org/wiki/Executable_and_Linkable_Format
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