cross armhf tangle

[Gary E. Miller]

Yo Hal!

On Sun, 02 Feb 2025 21:35:02 -0800
Hal Murray <halmurray at sonic.net> wrote:

> >> That was my first try.  It didn't work on BSD.  
> > Care to share what the failure was?  
> 
> It didn't know what a struct timeval was.

Did you set the required defines first?

Any place I can go to see the BSD man page and the include file contents?

> > Where can I find that man page?  
> 
> man timeval on this Linux box says:
> SYNOPSIS
>        #include <sys/time.h>

Odd. Not on Gentoo.  What linux are you on?
 
> Without the sys, it worked on Linux but not on BSD.

On Linux you usually need both.

> With the sys it works on everything I've tried so I moved on to other 
> things.

If it is working, why are we talking about it?

> > Oh, now I have context.  The only extra code for cross builds would
> > be the --march.  When you use --march then /usr/include/sys may not
> > be used for <sys/time.h>.  cc swaps sys directory to one approriate
> > to the target.   
> 
> Are you sure of that?

100%

>  I don't understand this area.

It is a PITA.

>  That's what I
> was expecting, but look in .gitlab-ci.yml in the cross-armhf area.
> There are a couple of runs that include:
>   --cross-cflags "-I/usr/include/ -I/usr/include/python${pyver}"
> Isn't that using the same headers?

No.  As I said in the part you trimmed, it is the "<sys/XXX.h>"
that gets swapped.

And, it is very, very, rare that you use your (usr/include) system
headers when cross compiling.

> My guess is that the same kernel header files work for all
> architectures and they are conditioned on #defines that the compiler
> provides.

But what if you are complaining for a BSD kernel on a Linux kernel?
Or building for a Linus 4.10 kernel on a 6.13 host?  As many embedded
systems do.  When cross-ccompiling you have to assume the worst.

> /usr/include/bits/timex.h has stuff like this
>   # if defined __USE_TIME64_REDIRECTS || (__TIMESIZE == 64 &&
> __WORDSIZE == 32)
> Where do they come from?

Oh boy.  You have not been following along.  The short answer
is that variable starting with "__" are reserved for the system
and you should never touch tehem.

So don't touch them!  Those are usually set from the --march=
option to fit the ABI.

> "gcc -dM -E -" tells you the compiler predefines.  397 of them on
> this box.  But no __TIMESIZE or __WORDSIZE

1.  You forgot the important part: --march=
2.  gcc does not define them.  The (proper) include files do, using
    defines that gcc sets from the ABI (--marh-)

> [After more grepping...]
> /usr/include/bits/wordsize.h says
> /* Determine the wordsize from the preprocessor defines.  */
> 
> #if defined __x86_64__ && !defined __ILP32__
> # define __WORDSIZE     64
> #else
> # define __WORDSIZE     32

Note that x86_64 and ILP32 are part of the selected (--march) ABI.

> Similar stuff in /usr/include/bits/timesize.h

And a thousand other places.  You are many layers away from user
configurable defines.

RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
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