[LLD][MachO] Do not run Mach-O tests on big-endian hosts

[uweigand]

Summary

Currently, most Mach-O tests fail when executed on a big-endian host. This is because the Mach-O back-end does not perform the necessary byte swaps when accessing the (little-endian) binary file format.

To fix this properly would either require use of the various swapStruct routines from the BinaryFormat/MachO.h header, or else a re-write of those headers to use ulittle32 etc. data types.

For now, simply consider all Mach-O tests unsupported on big-endian hosts (specifically, SystemZ), to enable running the test suite at all on such hosts.

[oontvoo]

lld/test/MachO/lit.local.cfg

8–9

How about using the existing host-byteorder-little-endian/host-byteorder-big-endian?

either adding this:

REQUIRES: host-byteorder-little-endian

or just checking "host-byteorder-little-endian" in config.available_features ?

[uweigand]

Use sys.byteorder to test for big-endian hosts.

[uweigand]

lld/test/MachO/lit.local.cfg

8–9

Turns out those features are only available in the llvm test suite, not the lld test suite right now. I guess they could be added there, but for now I'm just directly checking sys.byteorder to identify big-endian hosts.

[oontvoo]

LG - thanks!

lld/test/MachO/lit.local.cfg

 # -*- Python -*-
 
 import os
 
+# FIXME: The MachO back-end currently does not respect endianness when
+# accessing binary data structures, and therefore only works correctly
+# on little-endian host systems.  Skip all tests on big-endian hosts.
+if sys.byteorder == 'big':
+    config.unsupported = True
+
 # We specify the most commonly-used archs and platform versions in our tests
 # here. Tests which need different settings can just append to this, as only
 # the last value will be used.
 #
 # Note however that this does not apply to `-syslibroot`: each instance of that
 # flag will append to the set of library roots. As such, we define a separate
 # alias for each platform.