[AIX] Avoid depending on objdump

[jsji]

Summary

On AIX, we are currently relying on objdump to detemine the
is_32_bit_windows.

objdump is not installed by default on AIX, it is creating problem to
depend on it, especially just for an always false detection on AIX.

So this patch simply provide a always false function to satify the
detection.

[jsji]

Remove empty line.

[daltenty]

llvm/utils/extract_symbols.py

131

Won't this break other platforms? This script could (and probably is) run on Windows with GNU toolchain (i.e. MINGW with GNU nm) and would fall in to this case and get incorrect results

[jsji]

Address comment, support non AIX for nm.

[jsji]

Update

[jsji]

Use correct syntax.

[daltenty]

llvm/utils/extract_symbols.py

129–130

This isn't really related to us using nm. Technically someone could target 32-bit windows from AIX using the GNU toolchain, though no one is actually going to do that, so let's clarify what we're doing is working around limitations of the system toolchain.

131

365

maybe let's just provide a default value before the search for AIX, rather than modifying the nm entry

[jsji]

Address comments.

[daltenty]

LGTM, thanks!

llvm/utils/extract_symbols.py

def readobj_is_32bit_windows(lib):
     output = subprocess.check_output(['llvm-readobj','-file-headers',lib],
                                      universal_newlines=True)
     for line in output:
         match = re.match('Format: (\S+)', line)
         if match:
             return (match.group(1) == 'COFF-i386')
     return False
 
+# On AIX, there isn't an easy way to detect 32-bit windows objects with the system toolchain,
+# so just assume false.
+def aix_is_32bit_windows(lib):
+    return False
+
 # MSVC mangles names to ?<identifier_mangling>@<type_mangling>. By examining the
 # identifier/type mangling we can decide which symbols could possibly be
 # required and which we can discard.
 def should_keep_microsoft_symbol(symbol, calling_convention_decoration):
     # Keep unmangled (i.e. extern "C") names
     if not '?' in symbol:
         if calling_convention_decoration:
             # Remove calling convention decoration from names
if __name__ == '__main__':
 
     # Determine the function to use to get the list of symbols from the inputs,
     # and the function to use to determine if the target is 32-bit windows.
     tools = { 'dumpbin' : (dumpbin_get_symbols, dumpbin_is_32bit_windows),
               'nm' : (nm_get_symbols, None),
               'objdump' : (None, objdump_is_32bit_windows),
               'llvm-readobj' : (readobj_get_symbols, readobj_is_32bit_windows) }
     get_symbols = None
-    is_32bit_windows = None
+    is_32bit_windows = aix_is_32bit_windows if sys.platform.startswith('aix') else None
     # If we have a tools argument then use that for the list of tools to check
     if args.tools:
         tool_exes = args.tools
     # Find a tool to use by trying each in turn until we find one that exists
     # (subprocess.call will throw OSError when the program does not exist)
     get_symbols = None
     for exe in tool_exes:
         try: