[PATCH] D50144: Add Windows support for the GNUstep Objective-C ABI V2.

[John McCall via Phabricator via cfe-commits]

rjmccall added inline comments.


================
Comment at: lib/CodeGen/CGBlocks.cpp:1276
+    InitVar->setSection(".CRT$XCLa");
+    CGM.addUsedGlobal(InitVar);
+  }
----------------
DHowett-MSFT wrote:
> rjmccall wrote:
> > Is the priority system not good enough?
> My reading of the LLVM language reference leads me to believe it’s only ordered per-module. If that’s the case, the benefit of emitting into `XC*` is that it provides guaranteed order over all linker input.
> 
> `llvm.global_ctors` excerpt:
> 
> > The functions referenced by this array will be called in ascending order of priority (i.e. lowest first) when the module is loaded.
> 
> Now if the priority system _is_ guaranteed over all linker input, will that guarantee hold for mixed Clang and CL objects?
Init priorities on ELF are preserved in the section name like `.init_array.200`, and the sections get sorted by that in the image — it's really a very similar trick to how it works with `.CRT$XC`.  Of the major formats, I think it's just Mach-O that doesn't have any built-in prioritization mechanism across object files.  But I don't know if LLVM actually tries to translate init priorities over into `.CRT$XC` suffices when targeting PE/COFF, and arguably that's good: init priorities as presented in LLVM right now are pretty specific to the ELF mechanism.  Long-term, maybe `llvm.global_ctors` should be generalized so that on ELF targets it takes an integer priority, on PE/COFF targets it takes a string, and on Mach-O it doesn't take anything at all; but I won't hold up this patch for that.

On the other hand, I tend to agree that maybe the best solution is for the backend to just take care of this and automatically create a global initializer to install non-function (or maybe non-function & `unnamed_addr`) `dllimport`ed symbols in global data.


Repository:
  rC Clang

https://reviews.llvm.org/D50144