Testing GLib cross compilation

[Owen Taylor <otaylor redhat com>]

I just finished what I hope is complete support in GLib for
cross-compilation. (Based on work by Dimi Shahbaz, Dan Kegel, 
Johannes Stezenbach, Amy Lin, and Daniel Egger.)

The changes greatly reduce the number of places where runtime
checks are needed, and add AC_CACHE_VAL() statements to 
allow overriding the remaining runtime checks from the
configure.in.

[ I suspect the number of required runtime checks could 
  probably be reduced even more with fallbacks to compile-time 
  checks and defaults; I mainly went for the obvious stuff
  in this pass. ]

Since my set of cross-compilation environments is rather 
limited (I have a partially working linux to mingw32 
environment), I'd appreciate it if people would try out
the changes so we can make sure that it actually is 
functional for GLib-2.2.0.

The changes are in CVS now, or will be in a GLIb-2.1.4
release that I plan on doing later today.

Appended is a draft of some documentation about cross-compilation
that I plan on adding to the GLib reference manual. It could
use some looking over.

Regards,
                                        Owen


==

Instructions for cross compiling GLib
=====================================

Cross-compilation is the proceess of compiling a program or
library on a different architecture or operating system then
it will be run upon. GLib is slightly more difficult to 
cross-compile than many packages because much of GLib is
about hiding differences between different systems. 

These notes cover things specific to cross-compiling GLib;
for general information about cross-compilation, see the
autoconf info pages.

GLib tries to detect as much information as possible about
the target system by compiling and linking programs without
actually running anything; however, some information GLib
needs is not available this way. This information needs
to be provided to the configure script via a "cache file".

As an example of using a cache file, to cross compile for
the "MingW32" Win32 runtine environment on a Linux system,
create a file 'win32.cache' with the following contents:

===
glib_cv_long_long_format=ll
glib_cv_stack_grows=no
===

Then execute the following commands:

===
PATH=/path/to/mingw32-compiler/bin:$PATH
chmod a-w win32.cache   # prevent configure from changing it
./configure --cache-file=win32.cache --target=mingw32
===

The complete list of cache file variables follows. Most
of these won't need to be set in most cases.

Cache file variables
====================

glib_cv_long_long_format=[ll/q/I64]

 Format used by printf and scanf for 64 bit integers. 'll' is 
 the C99 standard, and what is used by the 'trio' library
 that GLib builds if your printf() is insufficiently capable.
 Empty is possible, but not recommended.

glib_cv_stack_grows=[yes/no]

 Whether the stack grows up or down; defaults to "no", which works
 most places. If you are compiling for PA-RISC or various other 
 architectures, you'll have to change this.

glib_cv_working_bcopy=[yes/no]

 Whether your bcopy can handle overlapping copies. Only needs to be set 
 if you don't have memmove. (Very unlikely)

glib_cv_sane_realloc=[yes/no]
 
 Whether your realloc() conforms to ANSI C and can handle NULL as
 the first argument. Defaults to "yes" and probably doesn't need to be set.

glib_cv_have_strlcpy=[yes/no]

 Whether you have strlcpy that matches OpenBSD. Defaults to "no",
 which is safe, since GLib uses a builtin version in that case.

glib_cv_va_val_copy=[yes/no]
 
  Whether va_list can be copied as a pointer. If set to "no", 
  then memcopy will be used. Only matters if you don't have
  va_copy or __va_copy. (So, doesn't matter for GCC.) Defaults
  to "yes" which is slightly more common than "no".

glib_cv_rtldglobal_broken=[yes/no]
 
  Whether you have a bug found in OSF/1 v5.0. Defaults to "no".

glib_cv_uscore=[yes/no]

  Whether an underscore needs to be prepended to symbols when
  looking them up via dlsym. Only needs to be set if your system
  uses dlopen/dlsym.

ac_cv_func_posix_getpwuid_r=[yes/no]

  Whether you have a getpwuid_r function (in your C library,
  not your thread library) that conforms to the POSIX spec.
  (Takes a 'struct passwd **' as the final argument)

ac_cv_func_nonposix_getpwuid_r=[yes/no]

  Whether you have some variant of getpwuid_r that doesn't
  conform to to the POSIX spec, but GLib might be able to
  use (or might segfault.) Only needs to be set if 
  ac_cv_func_posix_getpwuid_r is not set. It's safest to set
  this to "no".

glib_cv_use_pid_surrogate=[yes/no]

 Whether to use a setpriority() on the PID of the thread as
 a method for setting the priority of threads. This only
 needs to be set when using POSIX threads.

ac_cv_func_printf_unix98=[yes/no]

 Whether your printf() family supports Unix98 style %N$
 positional parameters. Defaults to "no".

ac_cv_func_vsnprintf_c99=[yes/no]

 Whether you have a vsnprintf() with C99 semantics. (C99 semantics
 means returns the number of bytes that would have been written
 had the output buffer had enough space.). Defaults to "no".