attribute init_priority() should trigger warning on OS X

[ilg-ul]

Bugzilla Link	14991
Resolution	WONTFIX
Resolved on	Jan 22, 2013 13:28
Version	3.1
OS	MacOS X
CC	@asl,@DougGregor

Extended Description

After several tests I discovered that the standard Apple linker does not support reordering of constructors.

GCC has a configuration definition

#define SUPPORTS_INIT_PRIORITY 0

that triggers errors when attributes like

attribute((constructor(NNN)))
attribute ((init_priority (NNN)))

are used:

OS.cpp:16:57: error: constructor priorities are not supported
OS.cpp:35:59: error: 'init_priority' attribute is not supported on this platform

I think that clang should also trigger warnings, to notify the user that those attributes, although properly processed within the compilation unit, will be silently ignored by the Apple linker.

Liviu

[asl]

These attributes are supported on Apple platforms. They just work within the single module.

[ilg-ul]

Yes, I already mentioned this, but on GNU/Linux they work at the entire application level, and it would be nice to warn users that on OS X things are different, to avoid discovering it in the hard way.

It is more like a courtesy issue than a real bug, but such small details differentiate great programs from common ones.

[DougGregor]

This kind of warning doesn't belong in Clang. We can't warn about even a reasonable number of system-specific differences, so Clang would never be useful as a porting tool for such issues. So (at best) we'd end up with some set of warnings that isn't enough to be useful for someone porting, but generates a lot of noise for someone who has already done the porting effort. Warnings that have such a high false-positive rate (say, by warning about every init_priority attribute on the Mac) don't belong in the compiler.