Porting Newlib: Difference between revisions

According to the documentation, you should also redefine errno as an 'extern char':

#include <errno.h>

#undef errno

extern int errno;

Re-entrant versions of these are a bit harder and are outlined in the documentation.

Once the source was downloaded, I loaded up Cygwin. All that needs to be done here is to build newlib:

cd /usr/src

mkdir build-newlib

../newlib-''<version>''/configure --prefix=''<location to put libarary>'' --target=i586-elf

make all install

Simple! However, if you try linking a previously written program with newlib you'll get undefined references everywhere. Why? You haven't yet put your 'glue' into the newlib yet.

Finally you must write something called the CRT0, basically the startup code for the executable. My CRT0 is really simple (GAS syntax):

.global _start

.extern main

hlt

jmp lp

All programs must link this as the '''first''' object ([[Linker_Scripts|linker script]] to the rescue).

I suggest writing a simple test program, the following will suffice:

int main()

{

return 0;

}

Put a little bit of code into your system call interface to print the function number that has been called and look for any possible calls.