rnk added inline comments.
================
Comment at: lib/CodeGen/CGBlocks.cpp:1276
+ InitVar->setSection(".CRT$XCLa");
+ CGM.addUsedGlobal(InitVar);
+ }
----------------
mstorsjo wrote:
> rjmccall wrote:
> > DHowett-MSFT wrote:
> > > rjmccall wrote:
> > > > Is the priority system not good enough?
> > > My reading of the LLVM language reference leads me to believe it’s only
> > > ordered per-module. If that’s the case, the benefit of emitting into
> > > `XC*` is that it provides guaranteed order over all linker input.
> > >
> > > `llvm.global_ctors` excerpt:
> > >
> > > > The functions referenced by this array will be called in ascending
> > > > order of priority (i.e. lowest first) when the module is loaded.
> > >
> > > Now if the priority system _is_ guaranteed over all linker input, will
> > > that guarantee hold for mixed Clang and CL objects?
> > Init priorities on ELF are preserved in the section name like
> > `.init_array.200`, and the sections get sorted by that in the image — it's
> > really a very similar trick to how it works with `.CRT$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$XC` suffices
> > when targeting PE/COFF, and arguably that's good: init priorities as
> > presented in LLVM right now are pretty specific to the ELF mechanism.
> > Long-term, maybe `llvm.global_ctors` should be generalized so that on ELF
> > targets it takes an integer priority, on PE/COFF targets it takes a string,
> > and on Mach-O it doesn't take anything at all; but I won't hold up this
> > patch for that.
> >
> > On the other hand, I tend to agree that maybe the best solution is for the
> > backend to just take care of this and automatically create a global
> > initializer to install non-function (or maybe non-function &
> > `unnamed_addr`) `dllimport`ed symbols in global data.
> > But I don't know if LLVM actually tries to translate init priorities over
> > into .CRT$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.
>
> FWIW, for the MinGW targets, the same ELF-like priority system is used (or I
> think it's actually an older mechanism previously used on ELF); constructors
> are emitted in `.ctors`, and those with a priority go into sections named
> `.ctors.01234` where the number is 65535 minus the init priority specified.
> By making these zero padded, they get ordered right by the normal
> alphabetical sorting. MinGW CRT startup routines then have extra code to run
> constructors in the right order from the `.ctors` section, in addition to the
> normal `.CRT$XC` ones.
I filed a bug to turn the integers into strings on COFF:
https://bugs.llvm.org/show_bug.cgi?id=38552
Repository:
rC Clang
https://reviews.llvm.org/D50144
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