20.04 on mac M1

[Colin Watson]

On Wed, Oct 13, 2021 at 03:41:56PM -0400, Jerry Geis wrote:
> Hi Paul - thanks for the reply..  So I have
> /usr/alpha-linux-gnu/include/sys/io.h
> 
> but it must not be actually included when I compile as a standard include
> directory ???
> 
> if I add the -I/usr/alpha-linux-gnu/include to the compile - now - that
> does work.   Thanks!  Not sure why its not picking it up automatically.

Because Alpha is a totally different CPU architecture from ARM, and you
only have that file because you installed a package for cross-compiling
programs to run on Alpha.  If using that search path works for you, it
can only be by luck: the architecture-specific definitions it gives you
will be entirely wrong, because they're designed for a completely
different kind of computer.  I very strongly recommend against hacking
this search path into your build process.

<sys/io.h> only exists at all on a few architectures (Intel x86, IA64,
and Alpha).  A program that relies on it is simply not going to work on
ARM without more substantial porting work.  (Of course, if the program
you're trying to build isn't very carefully-written, then it's always
possible that it includes this header but doesn't actually use it.)

-- 
Colin Watson (he/him)                              [cjwatson at ubuntu.com]