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Difference between revisions of "Compiling on OpenWRT"
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**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. | **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 | ***-rpath in LDFLAGS = "-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 (from https://www.linuxtopia.org/online_books/an_introduction_to_gcc/gccintro_24.html); | ****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); | ||
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***--dynamic-linker | ***--dynamic-linker | ||
****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) | ****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, so use that path instead | ****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 (from https://community.arm.com/developer/ip-products/processors/b/processors-ip-blog/posts/file-not-found-when-executing-assembled-program) | ||
*****--dynamic-linker /usr/lib/gcc/arm-openwrt-linux-muslgnueabi/7.4.0/ld-musl-armhf.so.1 | *****--dynamic-linker /usr/lib/gcc/arm-openwrt-linux-muslgnueabi/7.4.0/ld-musl-armhf.so.1 | ||
****LD is not the same as GNU LD (https://en.wikipedia.org/wiki/Linker_(computing)#GNU_linker<nowiki/>) | ****LD is not the same as GNU LD (https://en.wikipedia.org/wiki/Linker_(computing)#GNU_linker<nowiki/>) | ||
***<nowiki/>-L in | ***<nowiki/>-L in LDFLAGS = "-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) | ||
***** | ***** | ||
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**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 | *ELF Definition: https://en.wikipedia.org/wiki/Executable_and_Linkable_Format | ||
== Example == | |||
* Create a file named ex.sh: nano ex.sh | |||
* Add the following directives (from the above section) and save it; | |||
<syntaxhighlight lang="text"> | |||
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 " | |||
</syntaxhighlight> | |||
* Create a "Hello World" source code file: nano hw.c | |||
* Add the following text and save it; | |||
<syntaxhighlight lang="text"> | |||
#include <stdio.h> | |||
int main(void) | |||
{ | |||
printf("\nHello, world!\n\n"); | |||
return 0; | |||
} | |||
</syntaxhighlight>The below two commands are from an OpenWRT example here: https://openwrt.org/docs/guide-developer/helloworld/chapter2 | |||
* Type this command: gcc -c -o hw.o hw.c -Wall | |||
* Type this command: gcc -o hw hw.o | |||
...and then run it: ./hw, which should produce the below output;<syntaxhighlight lang="text"> | |||
Hello, world! | |||
</syntaxhighlight> | |||