On Thu, Oct 15, 2020 at 9:39 AM Ross Burton <ross@xxxxxxxxxxxxx> wrote:
>
> AC_PATH_X and friends are unusual in autoconf in that they
> *explicitly* look into /usr/ for files (see _AC_PATH_X_DIRECT).
> Notable this is the *only* macro in autoconf that explicitly looks
> into /usr.
>
> To write the logic out in English: iterate through a long list of
> paths in /usr for a X11/Xlib.h file, and if that exists try a compile
> test. Then iterate through the same set of paths after s/include/lib/
> looking for anything with a library extension (.a .so .sl .dynlib .dll
> .la) and if one is found try a link test.
>
> The big failure case is in cross compilation situations using a
> sysroot where the target is binary compatible with the host. In this
> case AC_PATH_X will happily look at /usr and say that yes, X is
> available, even if the sysroot doesn't have X.
>
> My preferred solution would be to delete AC_PATH_X and friends and get
> everyone to use PKG_CHECK_MODULES(x11), but I can see that isn't a
> realistic solution. Because the failure case above is a real problem
> for us, we just delete all of that code. Does anyone have a better
> solution that would continue to work but not be so dramatically
> dependent on host assumptions?
The thing that comes immediately to mind, and which would be feasible
for 2.70, is to not run _AC_PATH_X_DIRECT when cross-compiling. I
don't think it's unreasonable to require people who want to
cross-compile X11 programs to either have the headers and libraries on
the cross-compiler's default search path, or use the --x-includes and
--x-libraries command line switches. It might also make sense for
_AC_PATH_X_XMKMF to look for ${ac_tool_prefix}-xmkmf rather than plain
xmkmf, except I don't know if that would break existing cross compile
build farms.
I don't think Autoconf itself knows anything about whether or not the
cross compiler is using a sysroot, so I don't think it would be
practical to refine this any further than just "cross compiling or
not".
zw
N.B. I would happily add PKG_CHECK_MODULES(x11) to _AC_PATH_X's set of
things it tries, if pkg.m4 wasn't a third-party library. Merging it
is not 2.70 material.
